12-O-tetradecanoyl-phorbol-13-acetate induction of the human collagenase gene is mediated by an inducible enhancer element located in the 5'-flanking region

Matrix metalloproteinase-1 is induced by epidermal growth factor in human bladder tumour cell lines and is detectable in urine of patients with bladder tumours

The matrix metalloproteinases are a family of enzymes that degrade the extracellular matrix and are considered to be important in tumour invasion and metastasis. The effect of epidermal growth factor (EGF) on matrix metalloproteinase-1 (MMP1) production in two human bladder tumour cell lines, RT112 and RT4, has been investigated. In the RT112 cell line, an increase in MMP1 mRNA levels was found after a 6-h incubation with EGF, and this further increased to 20-fold that of control levels at 24- and 48-h treatment with 50 ng ml(-1) of EGF. MMP2 mRNA levels remained constant over this time period, whereas in the RT4 cells no MMP2 transcripts were detectable, but MMP1 transcripts again increased with 24- and 48-h treatment with 50 ng ml(-1) of EGF. MMP1 protein concentration in the conditioned medium from both cell lines increased with 24- and 48-h treatment of the cells and the total MMP1 was higher in the medium than the cells, demonstrating that the bladder tumour cell lines synthesize and secrete MMP1 protein after continuous stimulation with EGF. MMP1 protein was detected in urine from patients with bladder tumours, with a significant increase in concentration with increased stage and grade of tumour. MMP1 urine concentrations may therefore be a useful prognostic indicator for bladder tumour progression.

Collagenase-3 induction in rat lung fibroblasts requires the combined effects of tumor necrosis factor-alpha and 12-lipoxygenase metabolites: a model of macrophage-induced, fibroblast-driven extracellular matrix remodeling during inflammatory lung injury

The mechanisms responsible for the induction of matrix-degrading proteases during lung injury are ill defined. Macrophage-derived mediators are believed to play a role in regulating synthesis and turnover of extracellular matrix at sites of inflammation. We find a localized increase in the expression of the rat interstitial collagenase (MMP-13; collagenase-3) gene from fibroblastic cells directly adjacent to macrophages within silicotic rat lung granulomas. Conditioned medium from macrophages isolated from silicotic rat lungs was found to induce rat lung fibroblast interstitial collagenase gene expression. Conditioned medium from primary rat lung macrophages or J774 monocytic cells activated by particulates in vitro also induced interstitial collagenase gene expression. Tumor necrosis factor-alpha (TNF-alpha) alone did not induce interstitial collagenase expression in rat lung fibroblasts but did in rat skin fibroblasts, revealing tissue specificity in the regulation of this gene. The activity of the conditioned medium was found to be dependent on the combined effects of TNF-alpha and 12-lipoxygenase-derived arachidonic acid metabolites. The fibroblast response to this conditioned medium was dependent on de novo protein synthesis and involved the induction of nuclear activator protein-1 activity. These data reveal a novel requirement for macrophage-derived 12-lipoxygenase metabolites in lung fibroblast MMP induction and provide a mechanism for the induction of resident cell MMP gene expression during inflammatory lung processes.

AP-1 factors play an important role in transformation induced by the v-rel oncogene

v-rel is the oncogenic member of the Rel/NF-kappaB family of transcription factors. The mechanism by which v-Rel induces transformation of avian lymphoid cells and fibroblasts is not precisely known. However, most models propose that v-rel disrupts the normal transcriptional regulatory network. In this study we evaluated the role of AP-1 family members in v-Rel-mediated transformation. The overexpression of v-Rel, c-Rel, and c-Rel delta resulted in a prolonged elevation of c-fos and c-jun expression and in a sustained repression of fra-2 at both the mRNA and protein levels in fibroblasts and lymphoid cells. Moreover, the transforming abilities of these Rel proteins correlated with their ability to alter the expression of these AP-1 factors. v-Rel exhibited the most pronounced effect, whereas c-Rel, with poor transforming ability, elicited only moderate changes in AP-1 levels. Furthermore, c-Rel delta, which exhibits enhanced transforming potential relative to c-Rel, induced intermediate changes in AP-1 expression. To directly evaluate the role of AP-1 family members in the v-Rel transformation process, a supjun-1 transdominant mutant was used. The supjun-1 mutant functions as a general inhibitor of AP-1 activity by inhibiting AP-1-mediated transactivation and by reducing AP-1 DNA-binding activity. Coinfection or sequential infection of fibroblasts or lymphoid cells with viruses carrying rel oncogenes and supjun-1 resulted in a reduction of the transformation efficiency of the Rel proteins. The expression of supjun-1 inhibited the ability of v-Rel transformed lymphoid cells and fibroblasts to form colonies in soft agar by over 70%. Furthermore, the expression of supjun-1 strongly interfered with the ability of v-Rel to morphologically transform avian fibroblasts. This is the first report showing that v-Rel might execute its oncogenic potential through modulating the activity of early response genes.

Rb binds c-Jun and activates transcription

The retinoblastoma protein (Rb) acts as a critical cell-cycle regulator and loss of Rb function is associated with a variety of human cancer types. Here we report that Rb binds to members of the AP-1 family of transcription factors, including c-Jun, and stimulates c-Jun transcriptional activity from an AP-1 consensus sequence. The interaction involves the leucine zipper region of c-Jun and the B pocket of Rb as well as a C-terminal domain. We also present evidence that the complexes are found in terminally differentiating keratinocytes and cells entering the G1 phase of the cell cycle after release from serum starvation. The human papillomavirus type 16 E7 protein, which binds to both c-Jun and Rb, inhibits the ability of Rb to activate c-Jun. The results provide evidence of a role for Rb as a transcriptional activator in early G1 and as a potential modulator of c-Jun expression during keratinocyte differentiation.

Regulation of tissue-degrading factors and in vitro invasiveness in progression of breast cancer cells

Hormone-independent growth and invasiveness represent phenotypic properties acquired during early progression of breast cancer. We compared human mammary adenocarcinoma cells, MCF-7, which are estrogen-dependent and poorly metastatic, with the estrogen-independent and highly metastatic subline, MCF7/LCC1, with regard to expression of tissue-degrading factors of the matrix metalloproteinase (MMP)-and urokinase (uPA)-dependent degradative pathways, as well as for their in vitro invasive properties. Both cell lines showed low constitutive mRNA expression of the MMP inhibitor TIMP-1. Baseline expression of TIMP-2 mRNA was also very low in MCF-7 cells, whereas the MCF7/LCC1 level was much higher (approximately 10-fold). Furthermore, both cell lines revealed low constitutive capacity to migrate in an in vitro invasion assay. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA; 100 nM) induced the mRNAs for TIMP-1 as well as for MMP-1, MMP-9, the uPA receptor, and the uPA inhibitor PAI-1, amongst which only the responses of MMP-9 and PAI-1 were cell-specific. The mRNA levels of MMP-9 and PAI-1 were approximately 10-fold and approximately 15-fold higher in MCF7/LCC1 cells compared to MCF-7 cells. The secretion of immunoreactive PAI-1 was considerably elevated (> 20-fold) in TPA-treated MCF7/LCC1 cells, whereas the TPA-dependent level of 92-kDa MMP-9 was only approximately 2-fold higher in MCF7/LCC1 cells than in MCF-7 cells. In both cell lines treatment with TPA was associated with an increase (approximately 10-fold) in in vitro migration, which in the MCF7/LCC1 cells was significantly attenuated by a reconstituted basement membrane extract (Matrigel). These data suggest that TPA-responsive in vitro invasive properties that are probably associated with PAI-1 expression may co-vary with progression from hormone-dependent to -independent breast cancer.

Cloning and characterization of a novel hepatitis B virus x binding protein that inhibits viral replication

The hepatitis B virus and the mammalian hepadnavirus genomes encode for a short open reading frame called x. Expression of the protein product (HBx) appears necessary for establishment of natural infection. However, in vitro studies have suggested a multifunctional role for HBx as an indirect transcriptional transactivator of a variety of different viral and cellular promoters. Indeed, HBx has no known direct DNA binding properties but may interact with transcription factors as well as activate intracellular signaling pathways associated with cell growth. To further address the possible functional role of HBx in the life cycle of hepatitis B virus, we performed an analysis using the yeast two-hybrid system to screen a cDNA library derived from a hepatocellular carcinoma cell line with a HBx fusion bait in an attempt to identify cellular partners that may bind to and alter the biologic properties of HBx. A HBx-interacting protein that specifically complexes with the carboxy terminus of wild-type HBx was identified and designated XIP. This 9.6-kDa protein is capable of binding to HBx in vitro, and transient and stable expression in hepatocellular carcinoma cells abolishes the transactivation properties of HBx on luciferase constructs driven by AP-1 and endogenous hepatitis B virus enhancer/promoter elements. Investigation of the role of XIP in hepatitis B virus replication in differentiated hepatocellular carcinoma cells revealed that XIP expression reduces wild-type hepatitis B virus replication to levels observed following transfection with an HBx-minus virus. In contrast, the replication levels of the duck hepatitis B virus, a hepadnavirus that lacks the x open reading frame, were unchanged in the context of XIP expression. We propose that one of the physiologic functions of the cellular protein XIP is to negatively regulate HBx activity and thus to alter the replication life cycle of the virus.

Absence of a persistently elevated 37 kDa fos-related antigen and AP-1-like DNA-binding activity in the brains of kainic acid-treated fosB null mice

Chronic stimulation of the nervous system or acute administration of kainic acid results in a persistent increase in AP-1-like DNA-binding activity in the brain. However, the composition and function of these AP-1 complexes remain controversial. By comparing wild-type and fosB-null mice treated with kainic acid, we establish that the complexes comprise JunD in association with an approximately 37 kDa Delta-FosB species. Delta-FosB was expressed persistently in neurons in many areas of the CNS, even though fosB mRNA only increased transiently. This implies that the 37 kDa protein is very stable. fosB-/- mice are predisposed to seizures. Therefore, the chronic expression of Delta-FosB elicited by kainic acid seizures may be indicative of a compensatory/protective role in the pathophysiology of epilepsy.

Differential influence of antiestrogens on the in vitro release of gelatinases (type IV collagenases) by invasive and non-invasive breast cancer cells

Matrix metalloproteinases (MMPs) play an important role in tumor cell invasion and cancer metastasis. Accordingly, a higher level of these enzymes has been associated with the invasive phenotype. In the present study the effect of the antiestrogens, Analog II (AII), ICI-182,780 (ICI), and tamoxifen (TAM), on the in vitro release of MMPs, particularly gelatinases A and B by the MDA-MB-231 (MDA) and MCF-7 (MCF) human breast cancer cell lines was investigated using a solid-phase radioassay and substrate gel zymography. Quantitatively, the enzyme activity was found to be higher in the incubation medium from estrogen receptor (ER)-negative and more metastatic MDA cells compared to ER-positive and less metastatic MCF cells. Tissue inhibitor of metalloproteinases-1 (TIMP-1) reduced the enzyme activity in media from both MDA (56.36%) and MCF (71.03%) cells. Differential antiestrogen effects on the two cell lines were observed following 4 days of treatment of cells at a concentration of 10(-6)M. The enzyme activity from MDA cells was not influenced by treatment with any of the antiestrogens, whereas, in MCF cells, ICI produced the greatest enzyme inhibition (47.93%), followed by AII (36.51%) and TAM (24.05%). Concurrent treatment of MCF cells with 17-beta-estradiol (10(-9)M) partially reversed the AII- and TAM-induced but did not alter ICI-induced inhibition of enzyme activity. Substrate gel zymography revealed that among the MMPs, the MDA cells released predominantly progelatinase A (72 kDa) along with minor bands of activated forms, 62 kDa and 59 kDa, whereas progelatinase B (92 kDa) was detected predominantly in the medium from MCF cells. Comparison of the overall antiestrogen effect indicates that ICI is the most potent inhibitor of enzyme activity in ER-positive MCF cells and that antiestrogen treatment may limit the metastatic potential of ER-positive breast cancer.

Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth

Breast cancers often progress from a hormone-dependent, nonmetastatic, antiestrogen-sensitive phenotype to a hormone-independent, antiestrogen- and chemotherapy-resistant phenotype with highly invasive and metastatic growth properties. This progression is usually accompanied by altered function of the estrogen receptor (ER) or outgrowth of ER-negative cancer cells. To understand the molecular mechanisms responsible for metastatic growth of ER-negative breast cancers, the activities of the transcription factor NF-kappaB (which modulates the expression of genes involved in cell proliferation, differentiation, apoptosis, and metastasis) were compared in ER-positive (MCF-7 and T47-D) and ER-negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines. NF-kappaB, which is usually maintained in an inactive state by protein-protein interaction with inhibitor IkappaBs, was found to be constitutively active in ER-negative breast cancer cell lines. Constitutive DNA binding of NF-kappaB was also observed with extracts from ER-negative, poorly differentiated primary breast tumors. Progression of the rat mammary carcinoma cell line RM22-F5 from an ER-positive, nonmalignant phenotype (E phenotype) to an ER-negative, malignant phenotype (F phenotype) was also accompanied by constitutive activation of NF-kappaB. Analysis of individual subunits of NF-kappaB revealed that all ER-negative cell lines, including RM22-F5 cells of F phenotype, contain a unique 37-kDa protein which is antigenically related to the RelA subunit. Cell-type-specific differences in IkappaB alpha, -beta, and -gamma were also observed. In transient-transfection experiments, constitutive activity of an NF-kappaB-dependent promoter was observed in MDA-MB-231 and RM22-F5 cells of F phenotype, and this activity was efficiently repressed by cotransfected ER. Since ER inhibits the constitutive as well as inducible activation function of NF-kappaB in a dose-dependent manner, we propose that breast cancers that lack functional ER overexpress NF-kappaB-regulated genes. Furthermore, since recent data indicate that NF-kappaB protects cells from tumor necrosis factor alpha-, ionizing radiation-, and chemotherapeutic agent daunorubicin-mediated apoptosis, our results provide an explanation for chemotherapeutic resistance in ER-negative breast cancers.

The c-Jun-induced transformation process involves complex regulation of tenascin-C expression

In cooperation with an activated ras oncogene, the site-dependent AP-1 transcription factor c-Jun transforms primary rat embryo fibroblasts (REF). Although signal transduction pathways leading to activation of c-Jun proteins have been extensively studied, little is known about c-Jun cellular targets. We identified c-Jun-upregulated cDNA clones homologous to the tenascin-C gene by differential screening of a cDNA library from REF. This tightly regulated gene encodes a rare extracellular matrix protein involved in cell attachment and migration and in the control of cell growth. Transient overexpression of c-Jun induced tenascin-C expression in primary REF and in FR3T3, an established fibroblast cell line. Surprisingly, tenascin-C synthesis was repressed after stable transformation by c-Jun compared to that in the nontransformed parental cells. As assessed by using the tenascin-C (-220 to +79) promoter fragment cloned in a reporter construct, the c-Jun-induced transient activation is mediated by two binding sites: one GCN4/AP-1-like site, at position -146, and one NF-kappaB site, at position -210. Furthermore, as demonstrated by gel shift experiments and cotransfections of the reporter plasmid and expression vectors encoding the p65 subunit of NF-kappaB and c-Jun, the two transcription factors bind and synergistically transactivate the tenascin-C promoter. We previously described two other extracellular matrix proteins, SPARC and thrombospondin-1, as c-Jun targets. Thus, our results strongly suggest that the regulation of the extracellular matrix composition plays a central role in c-Jun-induced transformation.

AP-1 transcriptional activity is regulated by a direct association between thioredoxin and Ref-1

Thioredoxin (TRX) is a pleiotropic cellular factor that has thiol-mediated redox activity and is important in regulation of cellular processes, including proliferation, apoptosis, and gene expression. The activity of several transcription factors is posttranslationally altered by redox modification(s) of specific cysteine residue(s). One such factor is nuclear factor (NF)-kappa B, whose DNA-binding activity is markedly augmented by TRX treatment in vitro. Similarly, the DNA-binding activity of activator protein 1 (AP-1) is modified by a DNA repair enzyme, redox factor 1 (Ref-1), which is identical to a DNA repair enzyme, AP endonuclease. Ref-1 activity is in turn modulated by various redox-active compounds, including TRX. We here report the molecular cascade of redox regulation of AP-1 mediated by TRX and Ref-1. Phorbol 12-myristate 13 acetate efficiently translocated TRX into the HeLa cell nucleus where Ref-1 preexists. This process seems to be essential for AP-1 activation by redox modification because co-overexpression of TRX and Ref-1 in COS-7 cells potentiated AP-1 activity only after TRX was transported into the nucleus by phorbol 12-myristate 13 acetate treatment. To prove the direct active site-mediated association between TRX and Ref-1, we generated a series of substitution-mutant cysteine residues of TRX. In both an in vitro diamide-induced cross-linking study and an in vivo mammalian two-hybrid assay we proved that TRX can associate directly with Ref-1 in the nucleus; also, we demonstrated the requirement of cysteine residues in the TRX catalytic center for the potentiation of AP-1 activity. This report presents an example of a cascade in cellular redox regulation.

Inhibition of activator protein 1 activity and neoplastic transformation by aspirin

Aspirin, along with its analgesic-antipyretic uses, is now also being considered for prevention of cardiovascular disease, cancer, and treatment of human immunodeficiency virus infection. Although many of aspirin's pharmacological actions are related to its ability to inhibit prostaglandin biosynthesis, some of its beneficial therapeutic effects are not completely understood. Transcription factor activator protein 1 (AP-1) is critical for the induction of neoplastic transformation and induction of multiple genes involved in inflammation and infection. We have used the JB6 mouse epidermal cell lines, a system that has been used extensively as an in vitro model for the study of tumor promotion and anti-tumor promotion, to study the anti-carcinogenesis effect of aspirin at the molecular level. Aspirin and aspirin-like salicylates inhibited the activation of AP-1 in the same dose range as seen for the inhibition of tumor promoter-induced transformation. The inhibition of AP-1 and tumor promoter-induced transformation in JB6 cells occurs through a prostaglandin independent- and an Erk1- or Erk2-independent pathway. The mechanism of AP-1 and transformation inhibition in this cell culture model may involve the elevation of H+ concentration. The inhibition effects on the activation of AP-1 activity by aspirin and aspirin-like salicylates may further explain the anti-carcinogenesis mechanism of action of these drugs.

Induction of apoptosis by the transcription factor c-Jun

c-Jun, a signal-transducing transcription factor of the AP-1 family, normally implicated in cell cycle progression, differentiation and cell transformation, recently has also been linked to apoptosis. To explore further the functional roles of c-Jun, a conditional allele was generated by fusion of c-Jun with the hormone-binding domain of the human estrogen receptor (ER). Here we demonstrate that increased c-Jun activity is sufficient to trigger apoptotic cell death in NIH 3T3 fibroblasts. c-Jun-induced apoptosis is evident at high serum levels, but is enhanced further in factor-deprived fibroblasts. Furthermore, apoptosis by c-Jun is not accompanied by an increase in DNA synthesis. Constitutive overexpression of the apoptosis inhibitor protein Bcl-2 delays the c-Jun-mediated cell death. The regions of c-Jun necessary for apoptosis induction include the amino-terminal transactivation and the carboxy-terminal leucine zipper domain, suggesting that c-Jun may activate cell death by acting as a transcriptional regulator. We further show that alpha-fodrin, a substrate of the interleukin 1beta-converting enzyme (ICE) and CED-3 family of cysteine proteases, becomes proteolytically cleaved in cells undergoing cell death by increased c-Jun activity. Moreover, cell-permeable irreversible peptide inhibitors of the ICE/CED-3 family of cysteine proteases prevented the cell death.

Cloning, sequencing and characterization of the 5'-flanking region of the human collagenase-3 gene

Collagenase-3 (matrix metalloprotease-13) is a recently discovered human collagenase produced in normal articular cartilage chondrocytes and thought to be involved in the pathological process of osteoarthritis. We have sequenced and characterized 1.6 kb of the human collagenase-3 gene 5'-flanking region. The transcription start site was located 22 bp upstream from the ATG start codon. Sequence analysis of the 5'-flanking region revealed the presence of the consensus recognition sites for the TATA and CCAAT DNA-binding proteins, activator protein-1 and E26 transformation specific/polyoma virus enhancer, as well as three core motifs of hormone response elements. Transient transfection assays demonstrated that a small fragment of 133 bp, containing the activator protein-1 and E26 transformation specific/polyoma virus enhancer sites promoted transcription in normal and osteoarthritic human chondrocytes with significantly higher activity than the original 1.6 kb fragment. Nucleotide sequence comparison of the promoter region of human collagenase-3 revealed a stronger similarity to the mouse collagenase-1 promoter than to the human collagenase-1 promoter.

CREB is activated by UVC through a p38/HOG-1-dependent protein kinase

Changes in environmental conditions such as the addition of growth factors or irradiation of cells in culture first affect immediate response genes. We have shown previously that short wavelength UV irradiation (UVC) elicits massive activation of several growth factor receptor-dependent pathways. At the level of the immediate response gene c-fos, these pathways activate the transcription factor complex serum response factor (SRF)-p62TCF which mediates part of the UV-induced transcriptional response. These studies have, however, suggested that more that one pathway is required for full UV responsiveness of c-fos. Using appropriate promoter mutations and dominant-negative cAMP response element (CRE)-binding protein (CREB), we now find that UVC-induced transcriptional activation depends also on the CRE at position -60 of the c-fos promoter and on the functionality of a CREB. Upon UV irradiation, CREB and ATF-1 are phosphorylated at serines 133 and 63, respectively, preceded by and dependent on activation of p38/RK/HOG-1 and of a p38/RK/HOG-1-dependent p108 CREB kinase. Although p90RSK1 and MAPKAP kinase 2 are also activated by UV, p90RSK1 does not, at least not decisively, participate in this signalling pathway to CREB and ATF-1 as it is not p38/RK/HOG-1 dependent, and CREB is a poor substrate for MAPKAP kinase 2 in vitro. On the basis of resistance to the growth factor receptor inhibitor suramin and of several types of cross-refractoriness experiments, the UVC-induced CREB/ATF-1 phosphorylation represents an as yet unrecognized route of UVC-induced signal transduction, independent of suramin-inhibitable growth factor receptors and different from the Erk 1,2-p62TCF pathway.

A novel, transformation-relevant activation domain in Fos proteins

We have previously demonstrated that transformation by Fos is critically dependent on an intact DNA-binding domain (bZip) and a functional N-terminal transactivation motif (N-TM). We now show that a novel motif (C-terminal transactivation motif [C-TM]) near the C terminus also plays an important role in both transformation and the activation of AP1-dependent transcription and that the hydrophobic amino acids in the C-TM are functionally essential. The C-TM is the most crucial element in the C-terminal transactivation domain in Fos, as indicated by its relative strength and context-independent function. The C-TM is clearly different from the previously identified HOB2 domain, located N terminally to the C-TM, and the C-terminally positioned TATA-binding protein-binding domain. We also show that the C-terminal transactivation domain strongly synergizes with the HOB1-like N-TM, even when both domains are present on different proteins within a dimeric complex, and that the C-TM plays a crucial role in this cooperation. These observations can be corroborated in a model in which multiple contacts with the basal machinery are established either to stabilize the transcription complex or to facilitate its sequential assembly.

Myb-Ets fusion oncoprotein inhibits thyroid hormone receptor/c-ErbA and retinoic acid receptor functions: a novel mechanism of action for leukemogenic transformation by E26 avian retrovirus

The E26 and avian erythroblastosis virus (AEV) avian retroviruses induce acute leukemia in chickens. E26 can block both erythroid and myeloid differentiation at an early multipotent stage. Moreover, E26 can block erythroid differentiation at the erythroid burst-forming unit/erythroid CFU (BFU-E/CFU-E) stage, which also corresponds to the differentiation stage blocked by AEV. AEV carries two oncogenes, v-erbA and v-erbB, whereas E26 encodes a single 135-kDa Gag-Myb-Ets fusion oncoprotein. v-ErbA is responsible for the erythroid differentiation arrest through negative interferences with both the retinoic acid receptor (RAR) and the thyroid hormone receptor (T3R/c-ErbA). We investigated whether Myb-Ets could block erythroid differentiation in a manner similar to v-ErbA. We show here that Myb-Ets inhibits both RAR and c-ErbA activities on specific hormone response elements in transient-expression assays. Moreover, Myb-Ets abrogates the inactivation of transcription factor AP-1 by RAR and T3R, another feature shared with v-ErbA. Myb-Ets also antagonizes the biological response of erythrocytic progenitor cells to retinoic acid and T3. Analysis of a series of mutants of Myb-Ets reveals that the domains of the oncoprotein involved in these inhibitory activities are the same as those involved in oncogenic transformation of hematopoietic cells. These data demonstrate that the Myb-Ets oncoprotein shares properties with the v-ErbA oncoprotein and that inhibition of ligand-dependent RAR and c-ErbA functions by Myb-Ets is responsible for blocking the differentiation of hematopoietic progenitors.

Regulation of matrix metalloproteinase-1 and tissue inhibitor of metalloproteinase-1 in MCF-7 cells: comparison with regulatory mechanisms of pS2 expression

Regulation of two genes involved in tumor invasion, the matrix metalloproteinase (MMP)-1 and the tissue inhibitor of MMP (TIMP)-1, by activators of protein kinase C (PKC) or protein kinase A (PKA) was studied in MCF-7 mammary adenocarcinoma cells. The basal mRNA expression was undetectable for MMP-1 and low for TIMP-1. Treatment of MCF-7 cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (100 nM) was associated with a high expression of MMP-1 mRNA, as well as an induction of the level of TIMP-1 mRNA (5- to 10-fold). In the presence of actinomycin D (AMD, 4.0 microM), an inhibitor of transcription, these stimulatory effects of TPA were abolished. Similar responses were observed when protein synthesis was inhibited by cycloheximide (CHX, 50 microM). In the presence of the cyclic AMP (cAMP) analogue N6-benzoyl (N6-Bzl)-cAMP (500 microM), the MMP-1 mRNA was unaffected and still below the level of detection, whereas a non-significant increase (< 2-fold) in TIMP-1 mRNA was observed. The level of pS2 mRNA, of which the induction by TPA in MCF-7 cells is a primary transcriptional event, was up-regulated (10- to 15-fold) by TPA (100 nM), whereas a much weaker increase (2- to 3-fold) was observed by treatment with N6-Bzl-cAMP (500 microM). Again, these stimulatory effects were counteracted by AMD (4.0 microM) and CHX (50 microM). These data suggest that activation of PKC but not of PKA may induce transcription of MMP-1 and TIMP-1, possibly by the synthesis of transcription factor(s), in transformed cells of epithelial origin.

The nuclear factor YY1 suppresses the human gamma interferon promoter through two mechanisms: inhibition of AP1 binding and activation of a silencer element

Our group has previously reported that the nuclear factor Yin-Yang 1 (YY1), a ubiquitous DNA-binding protein, is able to interact with a silencer element (BE) in the gamma interferon (IFN-gamma) promoter region. In this study, we demonstrated that YY1 can directly inhibit the activity of the IFN-gamma promoter by interacting with multiple sites in the promoter. In cotransfection assays, a YY1 expression vector significantly inhibited IFN-gamma promoter activity. Mutation of the YY1 binding site in the native IFN-gamma promoter was associated with an increase in the IFN-gamma promoter activity. Analysis of the DNA sequences of the IFN-gamma promoter revealed a second functional YY1 binding site (BED) that overlaps with an AP1 binding site. In this element, AP1 enhancer activity was suppressed by YY1. Since the nuclear level of YY1 does not change upon cell activation, our data support a model that the nuclear factor YY1 acts to suppress basal IFN-gamma transcription by interacting with the promoter at multiple DNA binding sites. This repression can occur through two mechanisms: (i) cooperation with an as-yet-unidentified AP2-like repressor protein and (ii) competition for DNA binding with the transactivating factor AP1.

E2A basic-helix-loop-helix transcription factors are negatively regulated by serum growth factors and by the Id3 protein

Id3, a member of the Id multigene family of dominant negative helix-loop-helix transcription factors, is induced sharply in murine fibroblasts by serum growth factors. To identify relevant targets of Id3 activity, the yeast two-hybrid system was used to identify proteins that dimerize with Id3. Four murine cDNAs were identified in the screen, all of which encode helix-loop-helix proteins: E12, E47, ALF1 and Id4. Co-immunoprecipitation assays confirm that Id3 interacts with E12, E47 and two alternative splice products of ALF1 in vitro. Id3 disrupts DNA binding by these proteins in vitro and blocks transcriptional activation by these factors in cultured murine cells. Additionally, Id3 shows evidence of interacting with the related proteins E2-2 and MyoD, but not c-Myc. These results suggest that Id3 can function as a general negative regulator of the basic-helix-loop-helix family of transcription factors exemplified by the 'E' proteins and MyoD. Although it was previously suspected that E2A is constitutively expressed, our data indicate that E2A is induced in quiescent fibroblasts, by growth factor withdrawal but not by contact inhibition of cell proliferation. These observations extend the role of Id3 in the functional antagonism of E2A-class transcription factors, and suggest that E2A proteins may mediate growth inhibition.

Stepwise transformation of rat embryo fibroblasts: c-Jun, JunB, or JunD can cooperate with Ras for focus formation, but a c-Jun-containing heterodimer is required for immortalization

Among the Jun family of transcription factors, only c-Jun displays full transforming potential in cooperation with activated c-Ha-Ras in primary rat embryo fibroblasts. c-Jun in combination with Ras can both induce foci of transformed cells from rat embryo fibroblast monolayers and promote the establishment of these foci as tumoral cell lines. JunB can also cooperate with Ras to induce foci but is unable to promote immortalization. We report here that JunD, in cooperation with Ras, induces foci with an efficiency similar to that of JunB. Artificial Jun/eb1 derivatives from each of the three Jun proteins were also analyzed. These constructs carry a heterologous homodimerization domain from the viral EB1 transcription factor and are thought to form only homodimers in the cell. We show here that these Jun/eb1 chimeras are potent transactivators of AP1 sites and that they can cooperate with c-Ha-Ras to induce foci. However, among all the Ras-Jun and Ras-Jun/eb1 combinations tested, only foci from Ras-c-Jun can be efficiently expanded and maintained as long-term growing cultures. Therefore, we suggest that a heterodimer containing c-Jun might be required for in vitro establishment of these primary mammalian cells.

Acidic pH enhances the invasive behavior of human melanoma cells

As a consequence of poor perfusion and elevated acid production, the extracellular pH (pHex) of tumors is generally acidic. Despite this, most in vitro experiments are still performed at the relatively alkaline pHex of 7.4. This is significant, because slight changes in pHex can have profound effects on cell phenotype. In this study we examined the effects of mildly acidic conditions on the in vitro invasive potential of two human melanoma cell lines; the highly invasive C8161, and poorly invasive A375P. We observed that culturing of either cell line at acidic pH (6.8) caused dramatic increases in both migration and invasion, as measured with the Membrane Invasion Culture System (MICS). This was not due to a direct effect of pH on the invasive machinery, since cells cultured at normal pH (7.4) and tested at acidic pH did not exhibit increased invasive potential. Similarly, cells cultured at acidic pH were more aggressive than control cells when tested at the same medium pH. These data indicate that culturing of cells at mildly acidic pH induces them to become more invasive. Since acid pH will affect the intracellular pH (pHin) and intracellular calcium ([Ca2+]in), we examined the effect of these parameters on invasion. While changes in [Ca2+]in were not consistent with invasive potential, the changes in pHin were. While these conditions decrease the overall amount of gelatinases A and B secreted by these cells, there is a consistent and significant increase in the proportion of the activated form of gelatinase B.

Identification of the interleukin-6/oncostatin M response element in the rat tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter

The rat tissue inhibitor of metalloproteinase 1 (TIMP-1) gene is expressed in rat hepatocytes, and this expression is up-regulated by interleukin 6 (IL-6). We report here the cloning of the 5' flanking region of the rat TIMP-1 gene and identification of an IL-6/oncostatin M (OSM) response element at -64 to -36 which functions in hepatic cells. Within this element we have identified two functional binding sites for transcription factors AP-1 (activatory protein-1) and STAT (signal transducer and activator of transcription). IL-6/OSM stimulation induces binding of a protein, identified as STAT3, to the IL-6/OSM response element, while binding of the AP-1 protein was constitutive. Binding sites for both AP-1 and STAT3 are necessary for full responsiveness of the TIMP-1 promoter to IL-6/OSM, as shown by deletion and mutation analysis. Furthermore, the entire IL-6/OSM response element conferred responsiveness onto a heterologous promoter, whereas this has not been observed when AP-1 and STAT elements were separately tested.

Collagen and collagenase gene expression in three-dimensional collagen lattices are differentially regulated by alpha 1 beta 1 and alpha 2 beta 1 integrins

The reorganization of extracellular matrix (ECM) is an important function in many biological and pathophysiological processes. Culture of fibroblasts in a three-dimensional collagenous environment represents a suitable system to study the underlying mechanisms resulting from cell-ECM interaction, which leads to reprogramming of fibroblast biosynthetic capacity. The aim of this study was to identify receptors that transduce ECM signals into cellular events, resulting in reprogramming of connective tissue metabolism. Our data demonstrate that in human skin fibroblasts alpha 1 beta 1 and alpha 2 beta 1 integrins are the major receptors responsible for regulating ECM remodeling: alpha 1 beta 1 mediates the signals inducing downregulation of collagen gene expression, whereas the alpha 2 beta 1 integrin mediates induction of collagenase (MMP-1). Applying mAb directed against different integrin subunits resulted in triggering the heterodimeric receptors and enhancing the normal biochemical response to receptor ligation. Different signal transduction inhibitors were tested for their influence on gel contraction, expression of alpha 1(I) collagen and MMP-1 in fibroblasts within collagen gels. Ortho-vanadate and herbimycin A displayed no significant effect on any of these three processes. In contrast, genistein reduced lattice contraction, and completely inhibited induction of MMP-1, whereas type I collagen down-regulation was unaltered. Calphostin C inhibited only lattice contraction. Taken together, these data indicate a role of tyrosine-specific protein kinases in mediating gel contraction and induction of MMP-1, as well as an involvement of protein kinase C in the contraction process. The data presented here indicate that different signaling pathways exist leading to the three events discussed here, and that these pathways do not per se depend upon each other.

Generation of truncated forms of the NG2 proteoglycan by cell surface proteolysis

NG2 is a chondroitin sulfate proteoglycan that is expressed on dividing progenitor cells of several lineages including glia, muscle, and cartilage. It is an integral membrane proteoglycan with a core glycoprotein of 300 kDa. In the present study we have characterized three molecular forms of the NG2 core protein expressed by different cell lines. Many cell lines that express the full length 300-kDa NG2 core protein also release a 290-kDa form into the medium. This species lacks the cytoplasmic domain but contains almost the entire ectodomain. Two core protein species, the intact 300-kDa form and a truncated 275-kDa form, are expressed at the surface of an NG2-transfected cell line U251NG52. The 275-kDa species lacks the cytoplasmic domain and at least 64 amino acids of the ectodomain. Mild trypsinization of B49 cells also generates the 275-kDa species, suggesting that this component is produced by proteolysis of the 300-kDa form. Conversion of the 300-kDa species to the 275-kDa form in U251NG52 cells is stimulated by reagents such as phorbol esters, which activate protein kinase C. Phorbol esters are also known to induce expression of metalloproteinases such as collagenase and stromelysin, which could be responsible for cleavage of the 300-kDa core protein. Although B49 cells do not spontaneously produce the truncated 275-kDa species, use of monoclonal antibodies against NG2 to block the interaction between NG2 and type VI collagen results in the appearance of the 275-kDa component in these cells. Thus the interaction between NG2 and type VI collagen, which contains a Kunitz-type proteinase inhibitor sequence in the alpha 3 chain, may protect the proteoglycan against proteolysis. This is consistent with the observed deficiency of U251NG52 cells in anchoring type VI collagen at the surface.

Doxorubicin-induced Id2A gene transcription is targeted at an activating transcription factor/cyclic AMP response element motif through novel mechanisms involving protein kinases distinct from protein kinase C and protein kinase A

We have recently shown that doxorubicin (Dox), an antineoplastic drug and an inhibitor of terminal differentiation of myogenic and adipogenic cells, induces expression of Id, a gene encoding a helix-loop-helix transcriptional inhibitor. In this study we have investigated the molecular mechanisms underlying Dox-induced Id2A expression. We have also attempted to determine whether the genetic responses to Dox are related to the UV response, a well-characterized set of reactions to UV and DNA-damaging compounds that is partly mediated by AP-1. Transient transfection of a series of deletions and point mutation derivatives of the human Id2A promoter sequence shows that two closely spaced and inverted short elements similar to an activating transcription factor (ATF) binding site or a cyclic AMP response element (CRE) are necessary and sufficient for a full response to Dox. We refer to this element as the IdATF site. Sequences containing an IdATF site conferred Dox inducibility on a minimal heterologous promoter. An electrophoretic mobility shift assay showed nuclear proteins specifically interacting with the IdATF sequence. While oligonucleotides containing either legitimate ATF/CRE or AP-1 binding sequences competed for binding, antibody supershift experiments suggested that neither CREB/ATF-1 nor AP-1 are major factors binding to IdATF. Several independent criteria suggest that Dox inducibility was independent of Ca2+/phospholipid-dependent protein kinase (protein kinase C), cyclic AMP-dependent protein kinase (protein kinase A), and tyrosine kinase. Moreover, we found that Dox also induces transcription from promoters of immediate-early genes through an AP-1-independent pathway. Taken together, our results suggest that Dox elicits a novel genetic response distinct from the classical UV response.

Structure of the human TIMP-3 gene and its cell cycle-regulated promoter

The gene encoding tissue inhibitor of metalloproteinases-3 (TIMP-3) is regulated during development, mitogenic stimulation and normal cell cycle progression. The TIMP-3 gene is structurally altered or deregulated in certain diseases of the eye and in tumour cells. A detailed knowledge of the TIMP-3 gene and its regulatory elements is therefore of paramount importance to understand its role in development, cell cycle progression and disease. In this study, we present the complete structure of the human TIMP-3 gene. We show that TIMP-3 is a TATA-less gene, which initiates transcription at one major site, is composed of five exons and four introns spanning a region of approximately 30 kb, and gives rise to three distinct mRNAs, presumably due to the usage of alternative polyadenylation signals. Using somatic cell hybrids the TIMP-3 locus was mapped to chromosomal location 22q13.1 We also show that the TIMP-3 5' flanking region is sufficient to confer both high basal level expression in growing cells and cell cycle regulation in serum-stimulated cells. While the first 112 bases of the promoter, which harbour multiple Sp1 sites, were found to suffice for high basal level activity, the adjacent region spanning positions -463 and -112 was found to be a major determinant of serum inducibility. These results provide an important basis for further investigations addressing the role of TIMP-3 in physiological processes and pathological conditions.

Induction of Ca2+/calmodulin-stimulated cyclic AMP phosphodiesterase (PDE1) activity in Chinese hamster ovary cells (CHO) by phorbol 12-myristate 13-acetate and by the selective overexpression of protein kinase C isoforms

The cAMP phosphodiesterase (PDE) activity of CHO cells was unaffected by the addition of Ca2+ +calmodulin (CaM), indicating the absence of any PDE1 (Ca2+/CaM-stimulated PDE) activity. Treatment with the tumour promoting phorbol ester phorbol 12-myristate 13-acetate (PMA) led to the rapid transient induction of PDE1 activity which attained a maximum value after about 13 h before slowly decreasing. Such induction was attenuated by actinomycin D. PCR primers were designed to hybridize with two regions identified as being characteristic of PDE1 forms found in various species and predicted to amplify a 601 bp fragment. RT-PCR using degenerate primers allowed an approx. 600 bp fragment to be amplified from RNA preparations of rat brain but not from CHO cells unless they had been treated with PMA. CHO cells transfected to overexpress protein kinase C (PKC)-alpha and PKC-epsilon, but not those transfected to overexpress PKC-beta I or PKC-gamma, exhibited a twofold higher PDE activity. They also expressed a PDE1 activity, with Ca2+/CaM effecting a 1.8-2.8-fold increase in total PDE activity. RT-PCR, with PDE1-specific primers, identified an approx. 600 bp product in CHO cells transfected to overexpress PKC-alpha and PKC-epsilon, but not in those overexpressing PKC-beta I or PKC-gamma. Treatment of PKC-alpha transfected cells with PMA caused a rapid, albeit transient, increase in PDE1 activity, which reached a maximum some 1 h after PMA challenge, before returning to resting levels some 2 h later. The residual isobutylmethylxanthine (IBMX)-insensitive PDE activity was dramatically reduced (approx. 4-fold) in the PKC-gamma transfectants, suggesting that the activity of the cyclic AMP-specific IBMX-insensitive PDE7 activity was selectively reduced by overexpression of this particular PKC isoform. These data identify a novel point of 'cross-talk' between the lipid and cyclic AMP signalling systems where the action of specific PKC isoforms is shown to cause the induction of Ca2+/CaM-stimulated PDE (PDE1) activity. It is suggested that this protein kinase C-mediated process might involve regulation of PDE1 gene expression by the AP-1 (fos/jun) system.

Keratinocytes modulate the biosynthetic phenotype of dermal fibroblasts at a pretranslational level in a human skin equivalent

In this study we investigated the influence of keratinocytes on the phenotype of fibroblasts in an in vitro human skin equivalent. Keratinocytes were seeded at the surface of fibroblast-populated mechanically restrained type I collagen gels (lattices). Lattices without keratinocytes were handled in parallel as controls. After 2 and 4 days in culture, the keratinocyte layer was removed and the steady-state level of the mRNA for the main extracellular matrix macromolecules and interstitial collagenase produced by the fibroblasts was measured by Northern and dot blot analysis. A 50% decrease in the amount of procollagen type I and type III mRNAs was observed after 2 and 4 days of coculture while collagenase gene expression was upregulated by 300% when compared with control lattices. No significant modulation of type IV and type VI collagen, elastin or laminin B1 mRNA levels was found. Fibronectin mRNA levels in fibroblasts were significantly increased only on day 4. All the observed changes could be reproduced using a conditioned medium collected from a lattice covered with keratinocytes added to a lattice containing fibroblasts alone. These results indicate that in an in vitro reconstituted skin, keratinocytes are able to modulate the biosynthetic phenotype of fibroblasts at a pretranslational level through a paracrine signalling pathway.

DNA binding specificity determinants in MADS-box transcription factors

The MADS box is a conserved sequence motif found in the DNA binding domain of a family of transcription factors which possess related but distinct DNA binding specificities. We investigated the basis of differential sequence recognition by the MADS-box proteins serum response factor (SRF), MCM1, and MEF2A, using chimeric proteins and site-directed mutants in conjunction with gel mobility shift and binding site selection assays. Deletion of sequences immediately N terminal to the SRF MADS box alters its preferred binding site to that of MEF2A, although the resulting protein still weakly binds SRF-specific sites: exclusive binding to MEF2 sites requires further mutations, at MADS-box residues 11 to 15. In contrast to SRF, the sequence specificity of MCM1 (and of MEF2A) is determined entirely by sequences within its MADS box, and mutation of only SRF MADS-box residue 1 is sufficient to alter its binding specificity to that of MCM1. However, changes at both MADS-box positions 1 and 11 to 15 are necessary and sufficient to alter the specificity of the MCM1 MADS box to that of MEF2, and vice versa. The role of SRF MADS-box residues which differ from those present in the other proteins was investigated by selection of functional SRF variants in yeast cells. SRF MADS-box position 1 was always a glycine in the variants, but many different sequences at the other nonconserved MADS-box residues were compatible with efficient DNA binding. We discuss potential mechanisms of DNA recognition by MADS-box proteins.

Inhibition of collagenase and stromelysin gene expression by interferon-gamma in human dermal fibroblasts is mediated in part via induction of tryptophan degradation

The expression of the matrix-degrading enzymes collagenase and stromelysin is modulated by a variety of biologic and pharmacologic agents. IFN-gamma has potent effects on metalloproteinase production and therefore may play an important role in preventing excessive connective tissue degradation during inflammation and repair. We investigated the mechanisms of collagenase and stromelysin regulation by IFN-gamma in human dermal fibroblasts. IFN-gamma (300 U/ml) prevented the stimulation of metalloproteinase gene expression by IL-1 beta. In addition, incubation of fibroblasts with IFN-gamma resulted in a marked increase in cellular indoleamine 2,3-dioxygenase (IDO) mRNA, a > 90% depletion of tryptophan, and a corresponding > 30-fold increase in the tryptophan metabolite kynurenine in the culture media. Reducing the concentration of tryptophan from 25 microM to 0 markedly diminished the ability of fibroblasts to increase collagenase and stromelysin mRNA and collagenase production in response to IL-1 beta. Addition of exogenous tryptophan (25-50 micrograms/ml) to cultures that had been tryptophan depleted by pretreatment with IFN-gamma for 48 h restored the fibroblast response to IL-1 beta or PMA, but had no effect on IFN-gamma-induced HLA-DR alpha chain mRNA expression. These results indicate that inhibition of collagenase and stromelysin gene expression by IFN-gamma in fibroblasts is associated with activation of IDO and enhanced cellular tryptophan metabolism. Tryptophan degradation and ensuing tryptophan depletion may account, at least in part, for the inhibitory effect of IFN-gamma on metalloproteinase production in dermal fibroblasts.

Production and localization of 92-kilodalton gelatinase in abdominal aortic aneurysms. An elastolytic metalloproteinase expressed by aneurysm-infiltrating macrophages

Abdominal aortic aneurysms (AAA) are characterized by disruption and degradation of the elastic media, yet the elastolytic proteinases involved and their cellular sources are undefined. We examined if 92-kD gelatinase, an elastolytic matrix metalloproteinase, participates in the pathobiology of AAA. Gelatin zymography of conditioned medium from normal, atheroocclusive disease (AOD), or AAA tissues in organ culture showed that all tissues produced 72-kD gelatinase. AOD and AAA cultures also secreted 92-kD gelatinase, but significantly more enzyme was released from AAA tissues. ELISA confirmed that AAA tissues released approximately 2-fold more 92-kD gelatinase than AOD tissue and approximately 10-fold more than normal aorta. Phorbol ester induced a 5.3-fold increase in 92-kD gelatinase secretion by normal aorta and AOD and an 11.5-fold increase by AAA. By immunohistochemistry, 92-kD gelatinase was not detected in normal aorta and was only occasionally seen within the neointimal lesions of AOD tissue. In all AAA specimens, however, 92-kD gelatinase was readily localized to numerous macrophages in the media and at the adventitial-medial junction. The expression of 92-kD gelatinase mRNA by aneurysm-infiltrating macrophages was confirmed by in situ hybridization. These results demonstrate that diseased aortic tissues secrete greater amounts of gelatinolytic activity than normal aorta primarily due to increased production of 92-kD gelatinase. In addition, the localization of 92-kD gelatinase to macrophages in the damaged wall of aneurysmal aortas suggests that chronic release of this elastolytic metalloproteinase contributes to extracellular matrix degradation in AAA.

Heat shock of human synovial and dermal fibroblasts induces delayed up-regulation of collagenase-gene expression

We investigated the effect of heat shock on the expression of the collagenase gene in normal human synovial and dermal fibroblasts. Heat shock (42-44 degrees C for 1 h) caused a marked increase in heat-shock protein 70 (HSP-70) mRNA levels, followed by a delayed increase in collagenase mRNA levels, in both cell types. Pretreatment with cycloheximide had no effect on the heat-shock-induced increase in HSP-70 mRNA expression, but abrogated the induction of collagenase mRNA during the recovery. To study the mechanisms of collagenase-gene induction by heat shock, the transcriptional activity of a collagenase-promoter-driven chloramphenicol acetyltransferase (CAT) reporter gene was examined in transient transfection experiments. Heat shock was followed by a > 2-fold increase in CAT activity driven by a 3.8 kb fragment of the collagenase promoter, or by a construct containing an AP-1 binding site. A mutation in the AP-1 binding site abolished the effect of heat shock. Electrophoretic-mobility-shift assays revealed a marked increase in DNA-binding activity specific for the AP-1 binding site in nuclear extracts prepared from synovial fibroblasts recovering from heat shock. These results indicate that heat shock causes a delayed increase in collagenase-gene expression in human fibroblasts, and suggests that this stimulation involves, at least in part, transcriptional activation through an AP-1 binding site. Heat shock appears to initiate a programme of cellular events resulting in collagenase-gene expression, and therefore may contribute to connective-tissue degradation in disease states.

Components of the nuclear signaling cascade that regulate collagenase gene expression in response to integrin-derived signals

We have shown previously that the expression of collagenase is upregulated in rabbit synovial fibroblasts cultured on a substrate of antibody to the alpha 5 chain of the alpha 5 beta 1 integrin fibronectin receptor or on the 120-kD cell-binding chymotryptic fragment of plasma fibronectin, but remains at basal levels in cells plated on intact plasma fibronectin. We now have identified some of the components of a signaling pathway that couples the fibronectin receptor to the induction of collagenase transcription. We studied the control of collagenase gene expression in cells adhering to the 120-kD fragment of fibronectin, to antifibronectin receptor antibody, or to plasma fibronectin by transiently introducing promoter-reporter constructs into rabbit synovial fibroblasts before plating cells on these matrices. The constructs contained segments of the human collagenase promoter regulating transcription of chloramphenicol acyl transferase. Expression of constructs containing the -1200/-42-bp segment or the -139/-42-bp segment of the collagenase promoter inserted upstream from the reporter gene was induced to similar extents in cells plated on the 120-kD fragment of fibronectin or on anti-fibronectin receptor antibody, relative to that in fibroblasts plated on fibronectin. The expression of the construct containing the -66/-42-bp segment of the promoter was not regulated and was similar to that of the parent pBLCAT2 plasmid, suggesting that the -139/-67 region of the collagenase promoter, which contains PEA3- and AP1-binding sites, regulates the transcription of collagenase caused by integrin-derived signals. Expression of a reporter construct containing only the PEA3 and AP1 sites in the collagenase promoter (-90/-67) also increased in cells plated on the 120-kD fragment of fibronectin or on anti-fibronectin receptor antibody, relative to that in cells plated on fibronectin. Mutations in either the AP1 or PEA3 site of this minimal promoter abrogated its activity in cells plated on these inductive ligands. Expression of c-fos mRNA increased within 1 h of plating cells on the 120-kD fibronectin fragment or on anti-fibronectin receptor antibody, relative to that in cells plated on fibronectin. c-Fos protein accumulated in the nuclei of fibroblasts within 10 min of plating on the 120-kD fibronectin fragment. The increase in c-Fos was required for the increase in collagenase in cells plated on the 120-kD fibronectin fragment: incubation of cells with antisense, but not sense, c-fos oligonucleotides diminished both basal and induced expression of the -139/-42 collagenase promoter-reporter construct and decreased expression of the endogenous collagenase gene.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural organization and chromosomal localization of the mouse collagenase type I gene

A clone containing genomic sequences of part of the murine collagenase type 1 (MMP-1) gene was isolated. It contains exons 1-6 encoding all the domains required for collagenase function and 9 kb of 5'-flanking sequences. The gene organization and exon/intron borders are highly similar to the already described human and rabbit MMP-1 genes. However, neither the intron sequences, nor the promoter region up to position -660 exhibit significant sequence homologies with rabbit and human MMP-1, except for an AP-1-binding site and two PEA-3 consensus sequences. Binding studies in vitro revealed that the AP-1-binding site is recognized by Fos/Jun heterodimers with very high affinity. By in situ hybridization the mouse MMP-1 gene was located to the A1-A2 region of chromosome 9 in proximity to the curly whiskers (cw) locus. Based on the lack of sequence homologies of the promoter and intron regions, and since the chromosomal localization of the mouse and human MMP-1 genes may not be syntenic, these data strongly support previous suggestions that the MMP-1 genes from mouse, compared with rabbit and human, have evolved from different ancestral genes. The presence of the AP-1- and PEA-3- binding sites in all mammalian MMP-1 genes isolated so far, may, however, suggest evolutionary selection for common regulatory mechanisms of MMP-1 transcription.

Transforming growth factor-beta reverses a posttranscriptional defect in elastin synthesis in a cutis laxa skin fibroblast strain

Skin fibroblasts from two cases of autosomal recessive cutis laxa (CL), having insignificant elastin production and mRNA levels, were challenged with transforming growth factor beta-1 (TGF-beta 1). Elastin production was brought from undetectable values to amounts typical of normal human skin fibroblasts in a dose-dependent fashion. Basic fibroblast growth factor (100 ng/ml) alone or in combination with TGF-beta 1 reduced elastin production and mRNA expression in CL skin fibroblasts more extensively than in normal cells. In situ hybridization showed that these effects were at the transcript level. One of the CL strains was examined in detail. Transcription rates for elastin were similar in normal and CL and unchanged by TGF-beta 1 or TGF-beta 2 (10 ng/ml), while in CL elastin mRNA half-life was increased > 10-fold by TGF-beta 2 and reduced 6-fold after TGF-beta 2 withdrawal, as compared with a control strain. Cycloheximide partially reversed elastin mRNA instability. These data are consistent with a defect in elastin mRNA stability that requires synthesis of labile factors or intact translational machinery, resulting in an extremely low steady state level of mRNA present in this strain of CL. Furthermore, TGF-beta can relieve elastin mRNA instability in at least one CL strain and elastin production defects in both CL strains.

Regulation of the expression of the VEGF/VPS and its receptors: role in tumor angiogenesis

Vascular endothelial growth factor (VEGF)/vascular permeability factor (VPS) plays a crucial role for the vascularization of tumors including breast cancers. Tumors produce ample amounts of VEGF, which stimulates the proliferation and migration of endothelial cells (ECs), thereby inducing tumor vascularization by a paracrine mechanism. VEGF receptors (VEGF-Rs) are highly expressed by the ECs in tumor blood vessels. VEGF expression can be induced in various cell types by a number of stimuli including hypoxia, differentiation, growth factors and tumor promoters of the phorbol ester class, such as TPA. The VEGF inductive pathways comprise kinases, oncogenes, tumor suppressor genes, and steroid hormone transcription factors, many of which seem to converge on the activator protein (AP-1) transcription factor. Much less is known about the regulation of VEGF-R expression, which is restricted to ECs. This expression is greatly enhanced in diseased tissue such as solid tumors. So far, it appears that growth factors, cytokines, and tumor promoters are involved in the control of VEGF-R expression. Here we review current knowledge about the regulation of the expression of VEGF and its receptors.

Immortalization-susceptible elements and their binding factors mediate rejuvenation of regulation of the type I collagenase gene in simian virus 40 large T antigen-transformed immortal human fibroblasts

Dramatic changes occur in expression of the type I collagenase gene during the process of immortalization in simian virus 40 large T antigen-transformed human fibroblasts (S. Imai and T. Takano, Biochem. Biophys. Res. Commun. 189:148-153, 1992). From transient transfection assays, it was determined that these changes involved the functions of two immortalization-susceptible cis-acting elements, ISE1 and ISE2, located in a 100-bp region about 1.7 kb upstream. The profiles of binding of an activator, Proserpine, to the enhancer ISE1 were similar in the extracts of young, senescent preimmortalized and immortalized cells. ISE2 contained both negative and positive regulatory elements located adjacent to each other. The positive regulatory element consisted of a tandem array of putative Ets family- and AP-1-binding sites. An activator, Pluto, interacted with this positive regulatory element and had an AP-1-related component as a complex. The binding activity of Pluto was predominantly detected only in the extract from senescent preimmortalized cells. In contrast, a repressor, Orpheus, which bound to the ATG-rich negative regulatory element of ISE2, was prominently detected in extracts from both young preimmortalized and immortalized cells and appeared to suppress transcription in an orientation-dependent manner. Thus, the interplay of Pluto and Orpheus was suggested to be crucial for regulation of the collagenase gene accompanying in vitro aging and immortalization. Proserpine seemed to interact with Pluto to mediate strong expression of the collagenase gene in cellular senescence. On the basis of these results, we propose a model for regulation of the collagenase gene during in vitro aging and immortalization.

Immortalization-susceptible elements and their binding factors mediate rejuvenation of regulation of the type I collagenase gene in simian virus 40 large T antigen-transformed immortal human fibroblasts

Dramatic changes occur in expression of the type I collagenase gene during the process of immortalization in simian virus 40 large T antigen-transformed human fibroblasts (S. Imai and T. Takano, Biochem. Biophys. Res. Commun. 189:148-153, 1992). From transient transfection assays, it was determined that these changes involved the functions of two immortalization-susceptible cis-acting elements, ISE1 and ISE2, located in a 100-bp region about 1.7 kb upstream. The profiles of binding of an activator, Proserpine, to the enhancer ISE1 were similar in the extracts of young, senescent preimmortalized and immortalized cells. ISE2 contained both negative and positive regulatory elements located adjacent to each other. The positive regulatory element consisted of a tandem array of putative Ets family- and AP-1-binding sites. An activator, Pluto, interacted with this positive regulatory element and had an AP-1-related component as a complex. The binding activity of Pluto was predominantly detected only in the extract from senescent preimmortalized cells. In contrast, a repressor, Orpheus, which bound to the ATG-rich negative regulatory element of ISE2, was prominently detected in extracts from both young preimmortalized and immortalized cells and appeared to suppress transcription in an orientation-dependent manner. Thus, the interplay of Pluto and Orpheus was suggested to be crucial for regulation of the collagenase gene accompanying in vitro aging and immortalization. Proserpine seemed to interact with Pluto to mediate strong expression of the collagenase gene in cellular senescence. On the basis of these results, we propose a model for regulation of the collagenase gene during in vitro aging and immortalization.

The retinoblastoma gene product RB stimulates Sp1-mediated transcription by liberating Sp1 from a negative regulator

Studies have demonstrated that the retinoblastoma susceptibility gene product, RB, can either positively or negatively regulate expression of several genes through cis-acting elements in a cell-type-dependent manner. The nucleotide sequence of the retinoblastoma control element (RCE) motif, GCCACC or CCACCC, and the Sp1 consensus binding sequence, CCGCCC, can confer equal responsiveness to RB. Here, we report that RB activates transcription of the c-jun gene through the Sp1-binding site within the c-jun promoter. Preincubation of crude nuclear extracts with monoclonal antibodies to RB results in reduction of Sp1 complexes in a mobility shift assay, while addition of recombinant RB in mobility shift assay mixtures with CCL64 cell extracts leads to an enhancement of DNA-binding activity of SP1. These results suggest that RB is directly or indirectly involved in Sp1-DNA binding activity. A mechanism by which RB regulates transactivation is indicated by our detection of a heat-labile and protease-sensitive Sp1 negative regulator(s) (Sp1-I) that specifically inhibits Sp1 binding to a c-jun Sp1 site. This inhibition is reversed by addition of recombinant RB proteins, suggesting that RB stimulates Sp1-mediated transactivation by liberating Sp1 from Sp1-I. Additional evidence for Sp1-I involvement in Sp1-mediated transactivation was demonstrated by cotransfection of RB, GAL4-Sp1, and a GAL4-responsive template into CV-1 cells. Finally, we have identified Sp1-I, a approximately 20-kDa protein(s) that inhibits the Sp1 complexes from binding to DNA and that is also an RB-associated protein. These findings provide evidence for a functional link between two distinct classes of oncoproteins, RB and c-Jun, that are involved in the control of cell growth, and also define a novel mechanism for the regulation of c-jun expression.

The retinoblastoma gene product RB stimulates Sp1-mediated transcription by liberating Sp1 from a negative regulator

Studies have demonstrated that the retinoblastoma susceptibility gene product, RB, can either positively or negatively regulate expression of several genes through cis-acting elements in a cell-type-dependent manner. The nucleotide sequence of the retinoblastoma control element (RCE) motif, GCCACC or CCACCC, and the Sp1 consensus binding sequence, CCGCCC, can confer equal responsiveness to RB. Here, we report that RB activates transcription of the c-jun gene through the Sp1-binding site within the c-jun promoter. Preincubation of crude nuclear extracts with monoclonal antibodies to RB results in reduction of Sp1 complexes in a mobility shift assay, while addition of recombinant RB in mobility shift assay mixtures with CCL64 cell extracts leads to an enhancement of DNA-binding activity of SP1. These results suggest that RB is directly or indirectly involved in Sp1-DNA binding activity. A mechanism by which RB regulates transactivation is indicated by our detection of a heat-labile and protease-sensitive Sp1 negative regulator(s) (Sp1-I) that specifically inhibits Sp1 binding to a c-jun Sp1 site. This inhibition is reversed by addition of recombinant RB proteins, suggesting that RB stimulates Sp1-mediated transactivation by liberating Sp1 from Sp1-I. Additional evidence for Sp1-I involvement in Sp1-mediated transactivation was demonstrated by cotransfection of RB, GAL4-Sp1, and a GAL4-responsive template into CV-1 cells. Finally, we have identified Sp1-I, a approximately 20-kDa protein(s) that inhibits the Sp1 complexes from binding to DNA and that is also an RB-associated protein. These findings provide evidence for a functional link between two distinct classes of oncoproteins, RB and c-Jun, that are involved in the control of cell growth, and also define a novel mechanism for the regulation of c-jun expression.

Heparin inhibits the induction of three matrix metalloproteinases (stromelysin, 92-kD gelatinase, and collagenase) in primate arterial smooth muscle cells

Heparin inhibits the migration and proliferation of arterial smooth muscle cells and modifies the extracellular matrix. These effects may be the result of heparin's effects on proteinases that degrade the matrix. We have previously reported that heparin inhibits the induction of tissue-type plasminogen activator and interstitial collagenase mRNA. We have investigated the possibility that heparin affects other members of the matrix metalloproteinase family. Phorbol ester increased the levels of mRNA of collagenase, 92-kD gelatinase and stromelysin as well as the synthesis of these proteins. These effects were inhibited by heparin, but not by other glycosaminoglycans, in a dose-dependent manner. The induction of these matrix metalloproteinases was also inhibited by staurosporine and pretreatment with phorbol ester indicating the involvement of the protein kinase C pathway. In contrast, the 72-kD gelatinase was expressed constitutively and was not affected by phorbol ester or heparin. Tissue inhibitor of metalloproteinase-1 was expressed constitutively and was slightly increased by phorbol ester. It was not affected by heparin. Thus, heparin inhibits the production of four proteinases (tissue plasminogen activator, collagenase, stromelysin and 92-kD gelatinase) that form an interdependent system capable of degrading all the major components of the extracellular matrix.

Hyperinducible human metallothionein promoter with a low level basal activity

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Activation of c-Jun transcription factor by substitution of a charged residue in its N-terminal domain

C-Jun is a cellular transcription factor that can control gene expression in response to treatment of cells with phorbol esters, growth factors, and expression of some oncogenes. The ability of c-Jun to catalyze the transcription of certain genes is controlled, in part, by changes in the phosphorylation state of specific amino acids in c-Jun. One of the major sites that is phosphorylated during signal response is Ser73. Here we show that substitution of a negatively charged aspartic acid residue at 73 constitutively increased transcriptional activity of c-Jun. The Asp73 substitution also enhanced its availability to bind to DNA in a whole cell extract without altering its intrinsic DNA binding activity since the intrinsic activity was unaltered for the c-Jun mutant proteins expressed in a bacterial system. The negatively charged Asp substitution may mimic the negative charge of a phosphorylated serine at 73. The substitution of an uncharged alanine at 73 resulted in lowered activities. The N-terminal end of c-Jun containing these substitutions was fused to the DNA-binding region of the bovine papilloma virus E2 protein, and was able to confer the same activation properties to the fusion protein at the heterologous E2 DNA-binding site. Ser73 lies in a region of c-Jun previously proposed to bind an uncharacterized inhibitor, perhaps related to a protein of approximately 17.5 kD that coprecipitates along with our c-Jun or the JunE2 fusion products.

Blocking of tumor promoter-induced AP-1 activity inhibits induced transformation in JB6 mouse epidermal cells

AP-1 transcriptional activity is stimulated by the transformation promoters phorbol 12-myristate 13-acetate ("12-O-tetradecanoylphorbol 13-acetate," TPA) and epidermal growth factor (EGF) in promotion-sensitive (P+) but not in promotion-resistant (P-) JB6 mouse epidermal cell lines. Although TPA stimulates expression of the jun and fos family genes, only c-jun expression shows higher elevation in P+ cells than in P- cells. The present study tests the hypothesis that induced AP-1 activity is required for tumor promoter-induced transformation in JB6 P+ cells. Both retinoic acid and the glucocorticoid fluocinolone acetonide inhibited basal and TPA-induced AP-1 activities that were tested with a stromelysin promoter-chloramphenicol acetyltransferase reporter gene in P+ cells. Since both retinoic acid and fluocinolone acetonide are active in inhibiting TPA-induced anchorage-independent transformation of P+ cells in the dose range that blocks TPA-induced AP-1 activity, their antipromoting effects may occur through inhibition of AP-1 activity. To test the hypothesis with a more specific inhibitor, stable clonal transfectants of P+ cells expressing dominant negative c-jun mutant encoding a transcriptionally inactive product were analyzed. All transfectants showed a block in TPA and EGF induction of AP-1 activity. All transfectants also showed inhibition of TPA-induced transformation, and most transfectants showed a block in EGF-induced transformation. These results indicate that AP-1 activity is required for TPA- or EGF-induced transformation. This work demonstrates that a specific block in induced AP-1 activity inhibits tumor promoter-induced transformation.

Regulation of matrix metalloproteinase expression in human vein and microvascular endothelial cells. Effects of tumour necrosis factor alpha, interleukin 1 and phorbol ester

Matrix metalloproteinases (MMPs) play a role in tissue remodelling and angiogenesis. We have investigated the expression and regulation of MMP-1 (interstitial collagenase), MMP-2 (gelatinase A), MMP-3 (stromelysin 1), MMP-7 (matrilysin), MMP-9 (gelatinase B) and their inhibitors TIMP-1 and TIMP-2 in human umbilical vein, femoral vein and microvascular endothelial cells, and compared these data with those obtained with human synovial fibroblasts. Non-stimulated vein endothelial cells expressed the mRNAs for MMP-1, MMP-2, TIMP-1 and TIMP-2. MMP-3 mRNA and protein were undetectable or only weakly expressed, but could be stimulated by the inflammatory mediator tumour necrosis factor alpha (TNF alpha). The expression of MMP-3 and MMP-1 was further enhanced by phorbol 12-myristate 13-acetate (PMA). Phorbol ester also induced TIMP-1 and MMP-9, the expression of the latter being further enhanced by TNF alpha or interleukin 1 alpha (IL-1 alpha). Similar stimulatory effects were observed in microvascular endothelial cells. Hence the inflammatory mediator TNF alpha induces/enhances the production of several matrix metalloproteinases in human endothelial cells. On the other hand, MMP-2 and TIMP-2 were not affected or were affected in a variable way by TNF alpha and/or phorbol ester, suggesting a dissimilar regulation of these proteins. The cyclic AMP-enhancing agent forskolin affected the production of MMPs in a cell-type-specific way. In human vein endothelial cells it enhanced the PMA-mediated induction of MMP-9, whereas it suppressed this induction in human microvascular endothelial cells and in synovial fibroblasts. On the other hand, forskolin suppressed the PMA-mediated induction of MMP-1 and MMP-3 in synovial fibroblasts, while it enhanced or did not affect this induction in various types of human endothelial cells. These observations may have implications for future pharmacological intervention in angiogenesis.

Distinct mechanisms for regulation of the interleukin-8 gene involve synergism and cooperativity between C/EBP and NF-kappa B

The interleukin-8 promoter is transcriptionally activated by interleukin-1, tumor necrosis factor alpha, phorbol myristate acetate, or hepatitis B virus X protein through a sequence located between positions -91 and -71. This region contains an NF-kappa B-like and a C/EBP-like binding site. We show here that several members of the NF-kappa B family, including p65, p50, p52, and c-Rel, can bind to this region, confirming an authentic NF-kappa B binding site in the interleukin-8 promoter. Further, C/EBP binds only weakly to the interleukin-8 promoter site. Electrophoretic mobility shift assays with proteins overexpressed in COS cells and with nuclear extracts from tumor necrosis factor alpha-stimulated HeLa cells demonstrated a strong cooperative binding of C/EBP to its site when NF-kappa B is bound to its adjacent binding site. Transfection studies lead to a model that suggests a highly complex regulation of interleukin-8 gene expression at multiple levels: independent binding of C/EBP and NF-kappa B to their respective sites, cooperative binding of C/EBP and NF-kappa B to DNA, and positive synergistic activation through the C/EBP binding site and inhibition through the NF-kappa B binding site by combinations of C/EBP and NF-kappa B. Thus, the ultimate regulation of interleukin-8 gene expression depends on the ratio of cellular C/EBP and NF-kappa B.

Distinct mechanisms for regulation of the interleukin-8 gene involve synergism and cooperativity between C/EBP and NF-kappa B

The interleukin-8 promoter is transcriptionally activated by interleukin-1, tumor necrosis factor alpha, phorbol myristate acetate, or hepatitis B virus X protein through a sequence located between positions -91 and -71. This region contains an NF-kappa B-like and a C/EBP-like binding site. We show here that several members of the NF-kappa B family, including p65, p50, p52, and c-Rel, can bind to this region, confirming an authentic NF-kappa B binding site in the interleukin-8 promoter. Further, C/EBP binds only weakly to the interleukin-8 promoter site. Electrophoretic mobility shift assays with proteins overexpressed in COS cells and with nuclear extracts from tumor necrosis factor alpha-stimulated HeLa cells demonstrated a strong cooperative binding of C/EBP to its site when NF-kappa B is bound to its adjacent binding site. Transfection studies lead to a model that suggests a highly complex regulation of interleukin-8 gene expression at multiple levels: independent binding of C/EBP and NF-kappa B to their respective sites, cooperative binding of C/EBP and NF-kappa B to DNA, and positive synergistic activation through the C/EBP binding site and inhibition through the NF-kappa B binding site by combinations of C/EBP and NF-kappa B. Thus, the ultimate regulation of interleukin-8 gene expression depends on the ratio of cellular C/EBP and NF-kappa B.

The PML-retinoic acid receptor alpha translocation converts the receptor from an inhibitor to a retinoic acid-dependent activator of transcription factor AP-1

We report here that the fusion of PML, a nuclear protein defined by the t(15;17) chromosomal translocation in acute promyelocytic leukemia, with retinoic acid receptor alpha (RAR alpha) changes the RAR alpha from a retinoic acid (RA)-dependent inhibitor to a RA-dependent activator of AP-1 transcriptional activity. The PML-RAR alpha chimera cooperates with c-Jun and, strikingly, with c-Fos to stimulate the transcription of both synthetic and natural reporter genes containing an AP-1 site. Stimulation is dependent on the concentration of RA and its dose-response curve is comparable to that for activation by RAR alpha of transcription on RA-responsive genes. Further, in the absence of RA, a circumstance in which RAR alpha has no effect on AP-1 activity, PML-RAR alpha is an inhibitor. Deletion of the dimerization, transactivation, or DNA-binding domains of c-Jun and removal of the PML dimerization domain in the PML-RAR alpha hybrid abrogates their transcriptional cooperatively. In view of the association between AP-1 activity and hemopoietic differentiation, we suggest that these properties of PML-RAR alpha could contribute to the leukemic phenotype and its response to RA.

Platelet-activating factor induces collagenase expression in corneal epithelial cells

Platelet-activating factor (PAF), a potent lipid mediator involved in inflammatory and immune responses, accumulates rapidly in response to injury in a variety of tissues, including the corneal epithelium. However, the precise role of this compound in the cascade of events following insult has not been defined. Here we examined the effect of PAF on gene expression in the epithelial cells of rabbit corneas in organ culture. We found that incubation with 100 nM methylcarbamoyl PAF, a nonhydrolyzable analog of PAF, produced rapid transient 2.8- and 3.5-fold increases in the expression of c-fos and c-jun, respectively, at 1 hr, followed by increased expression of the collagenase type I gene beginning at 3 hr and peaking at 14-fold by 8 hr. Addition of the protein-synthesis-inhibitor cycloheximide superinduced c-fos and c-jun, strongly potentiating the PAF effect, but inhibited the induction of collagenase type I expression, suggesting the existence of a transcriptional factor linking the two events. BN-50730, a selective antagonist of intracellular PAF-binding sites, blocked the expression of the immediate-early genes as well as the increase in collagenase type I mRNA. Our results suggest that one of the functions of PAF may be to enhance the breakdown of the extracellular matrix as a part of the remodeling process during corneal wound healing after injury. Pathologically, a PAF-induced overproduction of collagenase may be a factor in the development of corneal ulcers, as well as other pathophysiological conditions such as cartilage destruction in arthritis. If so, inhibitors of this signal-transduction pathway may be useful as tools for further investigation and, eventually, as therapeutic agents to treat such disorders.