Cellular transformation and the 'morphologic phenotype' of transformed cells

Extracellular Superoxide Dismutase Expression in Papillary Thyroid Cancer Mesenchymal Stem/Stromal Cells Modulates Cancer Cell Growth and Migration

Tumor stroma-secreted growth factors, cytokines, and reactive oxygen species (ROS) influence tumor development from early stages to the metastasis phase. Previous studies have demonstrated downregulation of ROS-producing extracellular superoxide dismutase (SOD3) in thyroid cancer cell lines although according to recent data, the expression of SOD3 at physiological levels stimulates normal and cancer cell proliferation. Therefore, to analyze the expression of SOD3 in tumor stroma, we characterized stromal cells from the thyroid. We report mutually exclusive desmoplasia and inflammation in papillary and follicular thyroid cancers and the presence of multipotent mesenchymal stem/stromal cells (MSCs) in non-carcinogenic thyroids and papillary thyroid cancer (PTC). The phenotypic and differentiation characteristics of Thyroid MSCs and PTC MSCs were comparable with bone marrow MSCs. A molecular level analysis showed increased FIBROBLAST ACTIVATING PROTEIN, COLLAGEN 1 TYPE A1, TENASCIN, and SOD3 expression in PTC MSCs compared to Thyroid MSCs, suggesting the presence of MSCs with a fibrotic fingerprint in papillary thyroid cancer tumors and the autocrine-paracrine conversion of SOD3 expression, which was enhanced by cancer cells. Stromal SOD3 had a stimulatory effect on cancer cell growth and an inhibitory effect on cancer cell migration, thus indicating that SOD3 might be a novel player in thyroid tumor stroma.

Cell Density-Dependent Increase in Tyrosine-Monophosphorylated ERK2 in MDCK Cells Expressing Active Ras or Raf

The extracellular signal-regulated kinase (ERK) is one of the principal hub proteins that transmit growth signals from upstream oncogene products including Ras and BRaf to downstream effector proteins. However, there are both reports supporting and refuting the increase in ERK activity in cancer tissues expressing the active Ras and BRaf proteins. We considered that the cell density might account for this discrepancy. To examine this possibility, we prepared Madin-Darby canine kidney (MDCK) cells that expressed an active HRas, NRas, KRas, or BRaf and an ERK biosensor based on the principle of Förster resonance energy transfer (FRET). As we anticipated, expression of the active Ras or BRaf increased ERK activity at low cell densities. However, the ERK activity was markedly suppressed at high cell densities irrespective of the expression of the active Ras or BRaf. Western blotting analysis with Phos-tag gel revealed the decrease of tyrosine and threonine-diphosphorylated active ERK and the increase of tyrosine-monophosphorylated inactive ERK at high cell density. In addition, we found that calyculin A, an inhibitor for PPP-subfamily protein serine/threonine phosphatases, decreased the tyrosine-monophosphorylated ERK. Our study suggests that PPP-subfamily phosphatases may be responsible for cell density-dependent ERK dephosphorylation in cancer cells expressing active Ras or BRaf protein.

Towards elucidation of functional molecular signatures of the adhesive-migratory phenotype of malignant cells

Over the years, malignant transformation has been investigated on multiple levels, ranging from clinical pathology to the underlying molecular mechanisms. In "zooming in" on this process, cancer biologists have focused their attention on the molecular and cellular manifestations of the "transformed phenotype", including the genomic instability of cancer cells, their deregulated transcriptional activity, their aberrant morphology and dynamics, and the altered signaling networks activated in them. Attempts to elucidate the mechanisms underlying malignant and metastatic transformation are primarily motivated by the desire to identify specific molecules and signaling pathways that can serve as targets for novel therapies. In recent years, such studies were reinforced by major technological and conceptual developments: novel and powerful tools for genomic and proteomic analysis have been developed, and advanced computational approaches offer "systems-level" integration of rich and complex biological datasets into meaningful functional networks. In this article, we consider the current and potential impact of these new experimental approaches and, in particular, the recent progress made in quantitative proteomics, to elucidate the mechanisms underlying the "transformed phenotype". We will primarily focus on the adhesion and migration of cancer cells, and their relationships to the deregulated growth, metastatic dissemination, and anchorage independence associated with malignant transformation.

In situ immunocytochemical detection of altered membrane composition induced by cell-cell contact in cultured mammalian cells

In cultured mammalian cells, both normal and transformed, cell-cell contact was shown to alter the detergent extractability of nuclear and plasma membranes detected using immunocytochemistry of fixed cells. This alteration occurred in each cell individually, occurred in less than 1 hour after altered cell-cell contact, and did not involve new protein or mRNA synthesis. These results indicate that composition of cellular membranes is highly affected by cell-cell contact and culture density. This suggests a possible role for alterations in membrane composition in the regulation of normal cell behavior, including signaling of contact inhibition of growth and movement, behaviors that are not effectively regulated by cell-cell contact in malignantly transformed cells.

Analysis of the suitability of calreticulin inducible HEK cells for adhesion studies: microscopical and biochemical comparisons

Calreticulin is a Ca(2+)-buffering ER chaperone that also modulates cell adhesiveness. In order to study the effect of calreticulin on the expression of adhesion-related genes, we created a calreticulin inducible Human Embryonic Kidney (HEK) 293 cell line. We found that fibronectin mRNA and both intra- and extra-cellular fibronectin protein levels increased following calreticulin induction. However, despite this increase in fibronectin, HEK293 cells did not assemble an extracellular fibrillar fibronectin matrix regardless of the level of calreticulin expression. Furthermore, HEK293 cells exhibited a poorly organized actin cytoskeleton, did not have clustered fibronectin receptors at the cell surface, and did not form focal contacts. This likely accounts for the lack of fibronectin matrix deposition by these cells regardless of calreticulin expression level. Vinculin abundance did not appreciably increase upon calreticulin induction and the level of active c-Src, a regulatory kinase of focal contacts, was found to be abundant and unregulated by calreticulin induction in these cells. The inability to form stable focal contacts and to commence fibronectin fibrillogenesis due to high c-Src activity may be responsible for the poor adhesive phenotype of HEK 293 cells. Thus, we show here that HEK293 cells are not suitable for microscopical studies of cell-substratum adhesions, but are best suited for biochemical studies.

Neoplastic transformation and tumorigenesis associated with overexpression of IMUP-1 and IMUP-2 genes in cultured NIH/3T3 mouse fibroblasts

Immortalization-upregulated protein 1 (IMUP-1) and immortalization-upregulated protein 2 (IMUP-2) genes have been recently cloned and are known to be involved in SV40-mediated immortalization. IMUP-1 and IMUP-2 genes were strongly expressed in various cancer cell lines and tumors, suggesting the possibility that they might be involved in tumorigenicity. To directly elucidate the functional role of IMUP-1 and IMUP-2 on neoplastic transformation and tumorigenicity, we stably transfected IMUP-1 and IMUP-2 into NIH/3T3 mouse fibroblast cells. Cellular characteristics of the neoplastic transformation were assessed by transformation foci, growth in soft agar, and tumor development in nude mice. We found that IMUP-1 and IMUP-2 overexpressing cells showed altered growth properties, anchorage-independent growth in soft agar and inducing tumor in nude mice. Furthermore, IMUP-1 and IMUP-2 transformants proliferated in reduced serum and shortened cell cycle. These results suggest that ectopic overexpression of IMUP-1 and IMUP-2 may play an important role in acquiring a transformed phenotype, tumorigenicity in vivo, and be related to cellular proliferation.

Increased expression of the Zn-finger transcription factor BTEB1 in human endometrial cells is correlated with distinct cell phenotype, gene expression patterns, and proliferative responsiveness to serum and TGF-beta1

Basic transcription element binding (BTEB, also designated BTEB1) protein is a member of the Sp-family of GC-box binding transcription factors that exhibit distinct patterns of expression in many cell types and tissues. A role for BTEB1 in the regulation of cell growth and gene transcription has been invoked, but little is known about the molecular mechanisms underlying these activities. The present study examined the functional consequences of high and low BTEB1 expression in the human endometrial carcinoma cell line Hec-1-A, by deriving stable clonal lines that expressed sense (S) and anti-sense (As) rat BTEB1 constructs. Clonal S lines, with BTEB1 mRNA and protein levels higher than in corresponding parent (N) and As lines, displayed enhanced DNA synthesis upon 3[H]-thymidine incorporation, in serum-containing but not in serum-free medium, and increased cell cycle kinetics, concomitant with the induction in expression of the genes for the cell cycle-associated components cyclin D1, PCNA, cyclin-dependent kinase (Cdk) inhibitor p21, and Cdk2. Compared to N and As lines, S lines also had diminished ability to grow in multi-layers and exhibited increased mRNA levels for plasminogen activator inhibitor-1 (PAI-1), secretory leukocyte protease inhibitor (SLPI), and tissue inhibitor of metalloproteinases (TIMP)-2. In serum-free medium, S, but not N nor As lines, had enhanced DNA synthesis with transforming growth factor (TGF)-beta1, albeit all lines demonstrated similar responses to insulin-like growth factor-I and to epidermal growth factor, respectively. The higher DNA synthesis in S relative to N and As, lines upon exogenous TGF-beta1 addition, was observed in concert with increased expression of cyclins D1 and E and p21, genes. Moreover, S and As lines had increased mRNA levels for TIMP-1, TIMP-2, PAI-1, and beta-catenin, and diminished SLPI, and to a lesser extent, Cdk4 mRNA levels, with TGF-beta1 treatment. These results suggest that BTEB1 may mediate cell growth, in part, by modulating gene expression levels of distinct cell cycle and growth-associated proteins. The correlation between serum- and TGF-beta1 induction of DNA synthesis with increased BTEB1 expression further suggests that BTEB1 may constitute an important downstream regulatory component of various signaling pathways utilized by serum-associated and other growth factors in endometrial epithelial cells.

Overexpression of Hp95 induces G1 phase arrest in confluent HeLa cells

Xp95, a protein recently identified in Xenopus laevis, is potentially involved in progesterone-induced Xenopus oocyte maturation. In this study, we cloned a human homologue of Xp95, designated Hp95, and examined the effect of its overexpression on the growth properties of human malignant HeLa cells which have lost the contact inhibition of cell proliferation. We observed that although HeLa cells did not undergo G1 phase arrest at any stage after confluence, they were able to downregulate their G1 phase CDK activities in response to confluence. When Hp95 was overexpressed in HeLa cells by transfection with a constitutive or an inducible expression vector containing a full-length Hp95 transgene, HeLa cells became able to undergo G1 phase arrest and form a monolayer culture after confluence. However, the G1 phase CDK activities in these Hp95 overexpressing cells were not inhibited further as compared to control cells after confluence. These results indicate that the defects in HeLa cells that cause the loss of contact inhibition of cell proliferation are in components downstream of the G1 phase CDKs and that overexpression of Hp95 counteracts some of these defects.

An ankyrin-like protein with transmembrane domains is specifically lost after oncogenic transformation of human fibroblasts

We have identified a novel transformation-sensitive mRNA, which is present in cultured fibroblasts but is lacking in SV40 transformed cells as well as in many mesenchymal tumor cell lines. The corresponding gene is located on human chromosome 8 in band 8q13. The open reading frame of the mRNA encodes a protein of 1119 amino acids forming two distinct domains. The N-terminal domain consists of 18 repeats that are related to the cytoskeletal protein ankyrin. The C-terminal domain contains six putative transmembrane segments that resemble many ion channels. This overall structure is reminiscent of TRP-like proteins that function as store-operated calcium channels. The novel protein with an Mr of 130 kDa is expressed at a very low level in human fibroblasts and at a moderate level in liposarcoma cells. Overexpression in eukaryotic cells appears to interfere with normal growth, suggesting that it might play a direct or indirect role in signal transduction and growth control.

Down-regulated proteins of mesenchymal tumor cells

To identify proteins that are lost during the establishment of the transformed phenotype of a tumor cell, we have prepared a subtracted cDNA library with mRNA from normal human fibroblasts and from their matched SV40 transformed counterparts. More than 40 clones were obtained that showed a dramatic reduction in their relative expression after oncogenic transformation. The proteins encoded by these clones could be grouped into four distinct classes: extracellular matrix proteins (fibronectin, beta ig-h3, collagen VI), enzymes (collagenase, urokinase), cytoskeletal proteins (vinculin, SM22) and regulatory proteins (beta-glycan, integrin-associated protein, myosin kinase, IGFBP-5). Six novel gene products were discovered during these experiments, including a novel serine protease, a zyxin-like protein, an ankyrin-like protein and a GTP-binding protein. Only four of all the transformation-sensitive cDNAs were consistently down-regulated when a variety of cell lines derived from spontaneous mesenchymal tumors was investigated: beta ig-h3, collagen VI, the novel ankyrin-like protein, and IGFBP-5. It is likely that these gene products play an important role in the maintenance of the normal phenotype.

Cyclic AMP-mediated inhibition of angiotensin II-induced protein synthesis is associated with suppression of tyrosine phosphorylation signaling in vascular smooth muscle cells

In the present study, we have examined the effect of increased cyclic AMP (cAMP) levels on the stimulatory action of angiotensin II (Ang II) on protein synthesis. Treatment with cAMP-elevating agents potently inhibited Ang II-induced protein synthesis in rat aortic smooth muscle cells and in rat fibroblasts expressing the human AT1 receptor. The inhibition was dose-dependent and was observed at all concentrations of the peptide. To explore the mechanism of cAMP action, we have analyzed the effects of forskolin and 3-isobutyl-1-methylxanthine on various receptor-mediated responses. Elevation of cAMP did not alter the binding properties of the AT1 receptor and did not interfere with the activation of phospholipase C or the induction of early growth response genes by Ang II. Likewise, Ang II-dependent activation of the mitogen-activated protein kinases ERK1/ERK2 and p70 S6 kinase was unaffected by cAMP. In contrast, we found that increased concentration of cAMP strongly inhibited the stimulatory effect of Ang II on protein tyrosine phosphorylation. Specifically, cAMP abolished Ang II-induced tyrosine phosphorylation of the focal adhesion-associated protein paxillin and of the tyrosine kinase Tyk2. These results identify a novel mechanism by which the cAMP signaling system may exert growth-inhibitory effects in specific cell types.

A zyxin-related protein whose synthesis is reduced in virally transformed fibroblasts

We have cloned the gene for a novel LIM-domain protein from human fibroblasts whose expression is substantially decreased in simian-virus-40-(SV40)-transformed cells. This protein has a calculated molecular mass of 61 kDa and comprises a proline-rich domain followed by three LIM motifs. It appears to be identical to the focal adhesion protein p83 that has recently been isolated and characterized from porcine and human platelets. Hybridization experiments demonstrate a very low degree of evolutionary conservation of its sequence between mammals and birds. It is therefore possible that the novel protein represents the human equivalent of the chicken protein zyxin as the two proteins display a very similar overall structure, although their amino acid sequences diverge markedly from each other. The repression of this zyxin-related protein in virally transformed fibroblasts may explain, at least in part, the dramatic morphological changes that occur at the cell surface and in the cytoskeleton of transformed cells.

Gap-junctional communication in normal and neoplastic prostate epithelial cells and its regulation by cAMP

Gap-junctional communication and expression of gap junction-forming proteins were investigated in normal human prostate epithelial cells and in several malignant prostate cell lines. In comparison with normal cells, gap-junctional communication in malignant cells, as assayed by the transfer of 443-Da fluorescent tracer Lucifer yellow, was either reduced or not detected. Malignant cells expressed mRNA transcripts for connexin (Cx) 43, whereas normal cells expressed mRNA transcripts for Cx32 and Cx40. In both normal and malignant cells, gap-junctional communication was enhanced twofold to fivefold by treatment with forskolin, an agent known to increase intracellular levels of cAMP. Immunocytochemical staining with a Cx43-specific antibody revealed that in malignant cells this enhancement correlated with the number of gap junctions and occurred without any qualitative or quantitative alteration in Cx43 mRNA or protein. Moreover, western blot analyses showed that both control and forskolin-treated malignant cells expressed only one form of Cx43. Our data suggest that gap-junctional communication in both normal and malignant prostate cells may be regulated by hormones that work via a cAMP-dependent signal transduction pathway. Thus, both normal and malignant cells offer a new experimental model system in which interactions between a hormonal form of cellular communication and intercellular communication mediated via gap junctions can be studied.

Immortalization of cat iris sphincter smooth muscle cells by SV40 virus: growth, morphological, biochemical and pharmacological characteristics

The purpose of this study was to establish immortalized cell cultures of cat iris sphincter smooth muscle cells for a model investigating ocular receptors and their signal transduction pathways. Cultured cat iris sphincter muscle cells were immortalized by viral transformation with SV40 virus and the morphological and immunocytochemical properties of the normal and immortalized cells were investigated. The transformed cell clone, SV-CISM-2, was further characterized biochemically and pharmacologically. The normal muscle cells showed characteristics of smooth muscle cells, as judged by their growth and the presence of smooth muscle alpha-actin and desmin. After seven passages the normal cells ceased to proliferate. In contrast, the immortalized cells retained their proliferative ability for more than 220 population doublings over 55 passages. The transformation phenotype in these cells was confirmed by their expression of the large T-antigen, the incorporation of viral DNA into cellular DNA, growth in agarose and in low-serum medium, and complete loss of contact inhibition. The immortalized cells expressed smooth muscle alpha-actin, desmin and MLC protein. Biochemical and pharmacological studies on the SV-CISM cells revealed the presence of several functional receptors including muscarinic cholinergic, beta-adrenergic, peptidergic (substance P and endothelin). Platelet-activating factor, and prostaglandin (PG). Muscarinic stimulation of these cells resulted in: (a) a dose-dependent increase in the release of arachidonic acid (AA) and (PGs) and enhancement in the production of inositol trisphosphate (IP3); and (b) a substantial increase in MLC phosphorylation (118%), an indicator of smooth muscle contractility. The stimulatory effects of carbachol on these responses were completely blocked by atropine, a muscarinic receptor antagonist. This study constitutes the first successful immortalization of iris sphincter smooth muscle cells. The SV-CISM-2 cells can serve as an important model system for investigations on the biochemical and pharmacological properties of receptors and their signal transduction pathways in smooth muscle. The advantage of these cells over normal iris sphincter cells is that they can be propagated over many generations without alterations in their morphological, biochemical and physiological characteristics.

AVP inhibits EGF-stimulated MAP kinase cascade in Madin-Darby canine kidney cells

We investigated the effects of epidermal growth factor (EGF) and arginine vasopressin (AVP) on Raf-1-MAP kinase cascade, including Raf-1-kinase (Raf-1-K), MAP kinase kinase (MAPKK), MAP kinase (MAPK) and S6 kinase (S6K) in Madin-Darby canine kidney (MDCK) cells. In a dose-dependent manner (10(-10) M to 10(-6) M), EGF increased autophosphorylation of Raf-1-K and activated MAPKK, MAPK and S6K. Sequential activation of these kinases was indicated by their peak times of activation (Raf-1-K 5 min; MAPKK 10 min; MAPK 15 min; and S6K 30 min). AVP (10(-9) M to 10(-6) M) inhibited EGF-stimulated MAP kinase cascade. 8-Bromo-cyclic AMP (cAMP) could mimic the inhibitory effect of AVP on EGF-stimulated MAP kinase cascade. These results were confirmed using H-89, an inhibitor of protein kinase A (PKA) that blocked the effect of AVP on EGF-stimulated MAPK activity. We conclude that AVP inhibits EGF-stimulated Raf-1-K, MAPKK, MAPK, and S6K activity via cAMP in MDCK cells. Our results indicate that MAP kinase cascade may play an important role in integrating the effects of AVP and EGF on distal tubule function.

The induction of apoptosis in human mammary luminal epithelial cells by expression of activated c-neu and its abrogation by glucocorticoids

The effects of expressing neu-T, a mutated constitutively activated form of c-neu, have been examined in the non-transformed conditionally immortalised human mammary luminal epithelial cell line, HB4a. A variant cell line, N4.1, which expressed neu-T, showed evidence of transformation, including partial loss of growth factor dependence and acquisition of anchorage-independent growth, but failed to give rise to tumours in nude mice, indicating that expression of neu-T alone was probably insufficient to cause tumorigenic progression to a full malignant phenotype. During characterisation of the N4.1 cell line, it was observed that under conditions of serum deprivation, it underwent apoptotic cell death, as demonstrated by light microscopy, flow cytometry and DNA gel electrophoresis. The induction of apoptotic cell death in the N4.1 cell line by serum deprivation was abrogated specifically by the addition of steroids with glucocorticoid activity but not any peptide growth factors studied. This study shows the induction of apoptosis by serum deprivation, and its abrogation by glucocorticoids occurring in human mammary luminal epithelial cells transformed by expression of neu-T, and implicates the involvement of receptor protein tyrosine kinases in an apoptotic signalling pathway in this cell type.

Regulation of Ras-mediated signalling: more than one way to skin a cat

A powerful combination of genetics and biochemistry has provided details of how Ras-directed signalling interacts with and is regulated by other cellular signalling pathways. This might ultimately lead to the control of deregulated signalling by oncogenic Ras. Recently, progress has been made in understanding the regulation of Ras-mediated activation of the Raf-1-ERK2 kinase cascade through crosstalk with protein kinase C and cyclic-AMP-dependent protein kinase.

Deciphering the MAP kinase pathway

MAP kinases (MAPK) are serine/threonine kinases which are activated by a dual phosphorylation on threonine and tyrosine residues. Their specific upstream activators, called MAP kinase kinases (MAPKK), constitute a new family of dual-specific threonine/tyrosine kinases, which in turn are activated by upstream MAP kinase kinase kinases (MAPKKK). These three kinase families are successively stimulated in a cascade of activation described in various species such as mammals, frog, fly, worm or yeast. In mammals, the MAP kinase module lies on the signaling pathway triggered by numerous agonists such as growth factors, hormones, lymphokines, tumor promoters, stress factors, etc. Targets of MAP kinase have been characterized in all subcellular compartments. In yeast, genetic epistasis helped to characterize the presence of several MAP kinase modules in the same system. By complementation tests, the relationships existing between phylogenetically distant members of each kinase family have been described. The roles of the MAP kinase cascade have been analyzed by engineering various mutations in the kinases of the module. The MAP kinase cascade has thus been implicated in higher eukaryotes in cell growth, cell fate and differentiation, and in low eukaryotes, in conjugation, osmotic stress, cell wall construct and mitosis.

Novel marine alkaloids from the tunicate Eudistoma sp. are potent regulators of cellular growth and differentiation and affect cAMP-mediated processes

Six novel alkaloids that contain a fused tetracyclic pyrido[2,3,4-kl]acridine ring system were purified recently from the Red Sea purple tunicate Eudistoma sp. Evaluation of the effects of these alkaloids on cultured neuroblastoma and fibroblast cells revealed that they possess potent growth regulatory properties, and affect cell shape and adhesion. In mouse neuroblastoma cells, the Eudistoma alkaloids inhibited cell proliferation and induced a process of differentiation during which the cells flattened onto the surface, increased considerably in size, and extended long neurites. In hamster fibroblasts the alkaloids slowed down cell multiplication, and caused an exceptional cell flattening or elongation. In a virus-transformed derivative of the hamster fibroblasts the alkaloids restored many aspects of normal cell growth and morphology. In addition, several of the alkaloids mimicked the effects of cAMP analogs on two well-characterized cAMP-mediated processes involved in hepatic glucose metabolism--inhibition of pyruvate kinase (PK) activity and induction of mRNA for phosphoenolpyruvate carboxykinase (PEPCK). All these effects suggest that the Eudistoma alkaloids may act on the cAMP signaling system. However, a single application of these compounds was sufficient to completely block cell multiplication and to induce and sustain differentiation and "reverse transformation". Furthermore, these effects were not readily reversible following removal of the drugs. In contrast, a single application of agents that mimic or elevate cAMP induced a transient response that waned with time in culture, and the effects induced by constant elevation of cAMP reverse rapidly following drug removal. We propose that the Eudistoma alkaloids cause growth inhibition, differentiation, and reverse transformation by modifying the activity state of proteins that are involved in the regulation of cell shape and adhesion and serve as a target for the cAMP and/or other second messenger systems.

cAMP antagonizes p21ras-directed activation of extracellular signal-regulated kinase 2 and phosphorylation of mSos nucleotide exchange factor

In fibroblasts, stimulation of receptor tyrosine kinases results in the activation of the extracellular signal-regulated kinase 2 (ERK2). The major signalling pathway employed by these receptors involves the activation of p21ras and raf-1 kinase. Here we show that in NIH3T3 and rat-1 fibroblasts, elevation of the intracellular cAMP level results in the inhibition of ERK2 activation induced by PDGF, EGF and insulin treatment. Analysis of various signalling intermediates shows that cAMP interferes at a site downstream of p21ras, but upstream of raf-1 kinase. Inhibition by cAMP depends on both the cAMP concentration and the absolute amount of p21ras molecules bound to GTP, suggesting a mechanism of competitive inhibition. Also TPA-induced, p21ras-independent, activation of raf-1 kinase and ERK2 is inhibited by cAMP. We have used the inhibitory effect of cAMP to investigate whether phosphorylation of mSos, a p21ras nucleotide exchange factor, is dependent on the activity of the raf-1 kinase/ERK2 pathway. We found that phosphorylation of mSos, as monitored by a mobility shift, is delayed with respect to p21ras and ERK2 activation and is inhibited by cAMP in a similar cell type- and concentration-dependent manner as the inactivation of ERK2. These results provide evidence for a model of p21ras-directed signalling towards ERK2 that feeds back on mSos by regulating its phosphorylation status and that can be negatively modulated by protein kinase A and positively modulated by protein kinase C action.

Alternate pathogenesis of systemic neoplasia in the bivalve mollusc Mytilus

The proliferative disease systemic neoplasia, also termed hemic neoplasia or disseminated sarcoma, was studied in four Puget Sound, Washington populations of the bay mussel (Mytilus sp.). Using flow cytometric measurement of DAPI-stained cells withdrawn from the hemolymph, DNA content frequency histograms were generated for 73 individuals affected by the disease. The cells manifesting systemic neoplasia were found to exist as either of two separate types, characterized by G0G1 phase nuclear DNA contents of either approximately 4.9 x haploid (pentaploid form) or approximately 3.8 x haploid (tetraploid form). The two disease forms were found to coexist in all four mussel populations sampled, with overall relative prevalences of 66% pentaploid form, 29% tetraploid form, and 5% exhibiting both disease forms simultaneously. These findings represent the first unequivocal demonstration of multiple cell types in a bivalve neoplasia. The two forms appear to represent separate pathogenetic processes rather than sequential stages of a single pathogenesis. Two cell cycling parameters associated with proliferative activity were employed to compare the alternate forms: (i) the percentage of cells assigned to the DNA Synthesis (S) phase of the neoplastic cell cycle, and (ii) the proportion of neoplastic cell mitotic figures in hemocytological preparations. Mean values for both parameters were significantly higher for mussels with the tetraploid form of the disease, suggesting a higher rate of proliferation relative to the pentaploid form. Qualitatively, cells of the tetraploid form contained slightly lower nuclear and cytoplasmic volumes compared to those of the pentaploid form. An observed wide variation in neoplastic cell nuclear size within either disease form may reflect the distribution of cells in the G0G1, S, and G2M phases of the cell cycle. Potential etiologic relationships between the two forms are discussed.

Alterations in the cAMP signal transduction pathway in mouse lung tumorigenesis

Alterations in the cAMP signal transduction pathway are associated with mouse lung neoplasia, cAMP effects are mediated by activating cAMP-dependent protein kinase isozymes, PKA I and PKA II. E9, a tumorigenic cell line, exhibited decreased PKA I levels compared to C10 cells, a nontumorigenic cell line of similar epithelial origin. Western immunoblots of PKA subunit proteins demonstrated low concentrations of both the catalytic (C) and regulatory (RI) PKA I subunits. Although RII (regulatory subunit of PKA II) concentrations were similar in both cell lines, RII from E9 cells was more highly phosphorylated than in C10 cells. RII phosphorylation status regulates cAMP activation of PKA II. Northern-blot analysis of mRNA content indicated diminished expression of both C and RI mRNA in E9 relative to C10 cells. Several endogenous PKA substrate proteins present in C10 cells were minimally phosphorylated by PKA in E9 cells. Forskolin, which raises cellular cAMP content, increased phosphorylation of a protein doublet in intact C10 cells, but not in E9 cells. Decreased PKA I expression and alterations in RII phosphorylation in lung neoplasia may contribute to anomalous regulation by cAMP, thereby diminishing cAMP-mediated growth inhibitory effects.

Role of site-selective cAMP analogs in the control and reversal of malignancy

Two isoforms of cAMP receptor protein, RI and RII, the regulatory subunits of cAMP-dependent protein kinase, transduce opposite signals, the RI being stimulatory and the RII being inhibitory of cell proliferation. In normal cells RI and RII exist at a specific physiological ratio whereas in cancer cells such physiological balance of these receptor proteins is disrupted. Reversal and suppression of malignancy can be achieved when the physiologic ratio of these intracellular signal transducers of cAMP is restored as shown by the use of site-selective cAMP analogs, antisense oligodeoxynucleotides or gene transfer, suggesting new approaches to cancer control.

Possible involvement of normal p21 H-ras in the insulin/insulinlike growth factor 1 signal transduction pathway

Expression of a mutant H-ras gene confers a transformed phenotype to rat-1 fibroblasts which is basically independent of exogenous growth factors (GFs). Rat-1 cells induced to express high levels of the normal H-ras gene were also found to display a transformed phenotype. In contrast to cells expressing mutant H-ras, these cells were dependent on GFs. We used this difference in GF dependence to analyze a possible involvement of exogenous GFs in H-ras function. Compared with untransformed rat-1 cells, cells overexpressing normal H-ras displayed an elevated response toward insulinlike growth factor 1 (IGF-1), insulin, and bombesin and an increased sensitivity toward phosphatidic acids. It was found that 8-bromo-cyclic AMP inhibited the responses to all GFs in rat-1 cells but had no effect on mutant-H-ras-transformed cells. In cells overexpressing normal H-ras, 8-bromo-cyclic AMP inhibited the responses to all GFs except those to insulin and IGF-1. This implies that overexpression of normal H-ras in the presence of insulin/IGF-1 is functionally similar to the expression of mutant H-ras, since mutant H-ras can circumvent this block by itself. These and other results strongly suggest a functional linkage between insulin/IGF-1 and normal p21 H-ras.

Possible involvement of normal p21 H-ras in the insulin/insulinlike growth factor 1 signal transduction pathway

Expression of a mutant H-ras gene confers a transformed phenotype to rat-1 fibroblasts which is basically independent of exogenous growth factors (GFs). Rat-1 cells induced to express high levels of the normal H-ras gene were also found to display a transformed phenotype. In contrast to cells expressing mutant H-ras, these cells were dependent on GFs. We used this difference in GF dependence to analyze a possible involvement of exogenous GFs in H-ras function. Compared with untransformed rat-1 cells, cells overexpressing normal H-ras displayed an elevated response toward insulinlike growth factor 1 (IGF-1), insulin, and bombesin and an increased sensitivity toward phosphatidic acids. It was found that 8-bromo-cyclic AMP inhibited the responses to all GFs in rat-1 cells but had no effect on mutant-H-ras-transformed cells. In cells overexpressing normal H-ras, 8-bromo-cyclic AMP inhibited the responses to all GFs except those to insulin and IGF-1. This implies that overexpression of normal H-ras in the presence of insulin/IGF-1 is functionally similar to the expression of mutant H-ras, since mutant H-ras can circumvent this block by itself. These and other results strongly suggest a functional linkage between insulin/IGF-1 and normal p21 H-ras.

Involvement of vimentin in the reverse transformation reaction

An organized cytoskeleton is required for the cAMP-induced reverse transformation reaction in CHO-K1 cells. In the course of the reaction a considerable fraction of the genome changes its nuclease sensitivity. The current paper presents the following evidence that cAMP-induced phosphorylation of vimentin is an early step in this reaction complex. (i) Vimentin is only slightly phosphorylated in transformed CHO-K1 cells but is heavily phosphorylated in normal fibroblasts. (ii) cAMP addition almost triples the vimentin phosphorylation of CHO-K1 cells but does not change that of normal cells. (iii) Vimentin phosphorylation is one of the earliest phenomena to occur after addition of cAMP to CHO-K1 cells, preceding the cell-stretching reaction and other manifestations of reverse transformation. (iv) Indirect immunofluorescence experiments demonstrate that vimentin appears as a condensed mass in transformed CHO-K1 cells but cAMP addition restores the filamentous structure characteristic of the normal fibroblast. (v) Other transformed cells unresponsive to reverse transformation by cAMP failed to demonstrate increased phosphorylation of vimentin on treatment with cAMP. These results support the proposed scheme that phosphorylation of cytoskeletal elements initiates a large-scale genetic regulatory action in which a substantial change in the spectrum of genome exposure and sequestration occurs. A function for intermediate filaments in reverse transformation is implied.

Role of colony-stimulating factors in the biology of acute myelogenous leukemia

A high proportion of acute myeloid leukemias (AML) recently investigated for their capacity to synthesize biologically active bioregulatory molecules was found to accumulate messenger (m) RNA and to produce membrane-bound or -secreted forms of stimulating factors for granulocyte, macrophage and mixed granulocyte-macrophage colony growth. Blast cells have also been found to secrete interleukin 1, tumor necrosis factor-alpha, interleukin 6, and to express receptors for various growth factors as well. However, growth factors like interleukin 2 and interleukin 3 have not been identified as AML products, and several other factors including interleukin 4, interleukin 5, etc. need further evaluation. Responsiveness of clonogenic leukemic cells to exogenous growth-promoting factors in vitro suggests a possible role of these biomolecules in the course of these disorders. Important evidence for the crucial role of growth factors, at least in some subtypes of AML, has been provided by demonstrating constitutive growth factor production by leukemic cells and their autonomous in vitro growth which is dependent on autocrine secretion of a specific growth factor. The concert of mechanisms providing stimulatory and inhibitory signals for hematopoiesis, which is adapted to the various physiological requirements of the organism, may have multiple defects in AML. This leads to successive steps of malfunctioning of cells, which finally express a fully malignant phenotype. In addition, these derangements also lead to defects in accessory cells on the level of mediator communication. However, there is evidence for autonomous growth promotion of AML blast by constitutive production of growth factors active in an autocrine fashion (GM-CSF, G-CSF, interleukin 6) and by recruitment of accessory cells to increase CSF supply (GM-CSF, G-CSF) via molecules such as interleukin 1 and TNF-alpha in a paracrine fashion. Molecular analysis of transformed hematopoietic cells has revealed changes of the genome, e.g., insertion of viral genetic information or cytogenetic fractures at DNA sites controlling growth factor gene activation. These events appear to be crucial in the induction of uncontrolled growth factor expression promoting oncogenic transformation of hematopoietic progenitor cells.

Regulation of proliferation in a murine colony-stimulating factor-dependent myeloid cell line: superinduction of c-fos by the growth inhibitor 8-Br-cyclic adenosine 3':5' monophosphate

We have investigated the effect of 8-Br-cyclic adenosine 3':5' monophosphate (cAMP), a pharmacological activator of cAMP-dependent protein kinase, on the proliferation and the nuclear proto-oncogene induction in a murine granulocyte macrophage colony-stimulating factor (GM-CSF)-dependent myeloid cell line. Cells were growth arrested by granulocyte macrophage colony-stimulating factor and serum deprivation and were allowed to proceed in the cell cycle by addition of the lymphokine in the presence or absence of 8-Br-cAMP. 3H-thymidine incorporation assays showed that addition of 8-Br-cAMP inhibited the entry of cells into S phase and the subsequent proliferation. Northern analysis showed that 8-Br-cAMP had opposite effects on c-fos and c-myc mRNA induction. 8-Br-cAMP induced c-fos in the absence of any GM-CSF. In the presence of GM-CSF, c-fos mRNA was superinduced (30-fold induction compared to four- to fivefold by each signal alone). On the contrary, 8-Br-cAMP was not able to induce c-myc in the absence of growth factor and hardly interfered with the induction of c-myc by GM-CSF. Phorbol myristate acetate (PMA), a pharmacological activator of the lipid and CA++-dependent protein kinase C, was shown to induce nuclear proto-oncogene mRNA in the GM-CSF-dependent cell line. We investigated the effect of 8-Br-cAMP on PMA-induced c-fos and c-myc mRNA levels. When both cAMP dependent and lipid-dependent kinase systems were co-stimulated in the absence of GM-CSF, c-fos message was again superinduced (60-fold induction). On the contrary, c-myc message induction by PMA was inhibited by 80% by coactivation of cAMP-dependent protein kinase with 8-Br-cAMP. Our data indicate that an antiproliferative signal induces or even superinduces c-fos message and hardly interferes with c-myc induction, suggesting that the intracellular pathways resulting in c-fos and c-myc induction may be distinct and that two different pathways can lead to c-fos induction, with synergistic effects when both are activated.

Inhibition of transforming activity of tyrosine kinase oncogenes by herbimycin A

We studied the effectiveness of herbimycin A, an inhibitor of the function of the temperature-sensitive src oncogene, to reverse the morphologies of chicken and mammalian cells transformed by various oncogenes. It was found that the antibiotic was effective against the cells transformed by tyrosine kinase oncogenes src, yes, fps, ros, abl, erbB, but did not reverse the transformed morphologies induced by oncogenes raf, ras, and myc. Moreover, decreases in phosphotyrosine content of the total cellular proteins and in 36K protein phosphorylation by herbimycin treatment supported the selective inhibition of the antibiotic on the transforming activity of tyrosine kinase oncogenes.

Variation in endoplasmic-reticulum-associated glycoproteins of carrot cells cultured in vitro

Glycoproteins extracted from microsomes of in-vitro-cultured cells of Daucus carota L. cv. US-Harumakigosun were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detected by peroxidase-conjugated concanavalin A. The appearance of a glycoprotein with Mr 31 000 (GP 31) was correlated with the ability of cells to form somatic embryos. GP 31 appeared in embryogenic cells cultured in 2,4-dichlorophenoxyacetic acid (2,4-D)-containing medium, but not in somatic embryos and non-embryogenic cells; it disappeared when the cultures were transferred to auxin-free medium. Another glycoprotein with Mr 32 000 (GP 32) was detected only in non-embryogenic cells, regardless of the presence or absence of 2,4-D. Both glycoproteins, GP 31 and GP 32, were associated with the rough endoplasmic reticulum and were extractable with 0.05% deoxycholate.

Establishment and characterization of a continuous murine uterine cervix cancer cell line metastatic to lymph nodes and lungs

The murine uterine cervix cancer (MUCC) cell line was derived from a chemically induced Kunming mouse uterine cervix cancer (U27) and maintained in culture on solid substrates for over 100 passages. Cultures were morphotypically heterogeneous and heteroploid, with a modal number of chromosomes = 80. Each cell showed at least two abnormal chromosomes. Immunogold-silver staining was positive for keratin, vimentin, and laminin but not for desmin. The population doubling time was 27.8 h with a saturation density of 3.2 X 10(5) cells/cm2 and a peak mitotic index of about 6%. MUCC cells produced colonies on tissue culture plastic (68%) and in soft agar (8%). MUCC cells were fully malignant inasmuch as they produced in syngeneic mice invasive tumors that reproducibly were metastatic to lymph nodes and lungs. The MUCC cell line is the first mouse cervix cancer cell line useful for the study of invasion and metastasis.

Possible involvement of reorganization of actin filaments, induced by tumor-promoting phorbol esters, in changes in colony shape and enhancement of proliferation of cultured epithelial cells

Tumor promoters are known to induce reorganization of actin, morphological changes and enhancement of proliferation of epidermal cells in vivo. In this study, we have examined the effects of tumor promoters on these events to clarify the role played by the organization of actin filaments in the regulation of the shape and growth of colonies of epithelial cells in culture. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) caused a change in the shape of colonies of FL and Madin-Darby canine kidney (MDCK) cells within 6 hr. Changes in the shape of colonies were consistent with the morphological change of individual cells and the dissociation of groups of cells in the colonies. Addition of TPA also caused reorganization of actin filaments after 2 hr, and it caused enhancement of proliferation of FL and MDCK cells after 48 hr but did not cause any such changes in KB cells. However, the binding affinities of 4 beta-phorbol 12,13-dibutyrate (PDBu) to FL and MDCK cells were similar to that of PDBu to KB cells. Related tumor promoters such as phorbol 12,13 didecanoate (PDD) and mezerein caused effects similar to those caused by TPA. In contrast, nontumor promoting phorbol esters, such as 4 alpha-PDD and phorbol, had no effect. Cyclic AMP blocked the TPA-induced changes in FL and MDCK cells. These results suggest that TPA-induced reorganization of actin filaments which can be inhibited by cyclic AMP results in changes in the shape of colonies and enhancement of proliferation.

Cellular signal transduction and the reversal of malignancy

Animal cells contain only a few defined molecular systems that transduce hormonal and growth signals from the external environment to the intracellular milieu to regulate cellular growth and differentiation. Among the most ubiquitous of these "second messenger" pathways are those utilizing cyclic AMP and phosphatidylinositide turnover. The former activates protein kinase A, while the latter leads to the activation of protein kinase C and mobilization of intracellular calcium. Lesions induced by oncogenes in signal transduction systems may be responsible for the cancerous transformation of cells. In many tumor cell lines, including some transformed by the ras and sis oncogenes, activation of protein kinase A by elevation of cyclic AMP or activation of protein kinase C by addition of phorbol esters can restore many normal aspects of growth and morphology. Such "reverse transformation" is accompanied by the phosphorylation of unique cellular proteins and alterations in the phosphoinositide cycle. Molecular mechanisms by which activation of signal transduction systems can attenuate the malignant phenotype are considered in the context of cellular growth and differentiation.

Altered type I protein kinase in adhesion defective CHO cell variants

ADv cells are Chinese hamster ovary (CHO) cell variants which cannot adhere to fibronectin coated substrata (Harper & Juliano: J. Cell Biol., 1980; Nature 1981a,b). We have shown that the defect in some clones of ADv cells is distal to the initial interaction between fibronectin and its cell surface receptors (Cheung and Juliano: Exp. Cell Res., 1984), and that it extends to fibronectin mediated aggregation and endocytosis. The adhesion defect in some ADv clones can be corrected by raising intracellular cAMP levels (Cheung & Juliano: J. Cell Physiol., 1985). Here we examine the protein kinase activities and phosphorylation patterns in an adhesion defective variant clone ADv F11CA11. Analysis of the cAMP dependent protein kinase activity (cAdPK) in crude extracts of F11CA11 cells shows an apparent increase in K (activation) as compared to wild type (WT) CHO cell extracts. Further, the DE-52 cellulose chromatography profile of cAdPK in the F11CA11 variant is markedly different from WT in that the type I cAdPK peak elicited by 1 microM cAMP is essentially missing in F11CA11, while the type II cAdPK peak is similar to that in WT. Raising the cAMP level to 100 microM elicits a type I peak in F11CA11 with about 45% of the activity of the WT peak. Binding studies with 3H-cAMP reveal that the type I peak in F11CA11 has a Kd of 1.7 X 10(-8) M as compared to 2.0 X 10(-9) M for WT, whereas the type II peak Kd is approximately 1 X 10(-9) M for both WT and F11CA11. Two-dimensional polyacrylamide gel analysis of 32Pi labeled WT cells and F11CA11 cells with or without cAMP treatment reveals the presence of a protein(s) of 50 kilodaltons which is phosphorylated in WT cells and in cAMP treated F11CA11 cells but not in untreated F11CA11 cells. These findings, coupled with our previous observations, strongly indicate that the adhesion defect in ADvF11CA11 cells is associated with an altered type I cAdPK having lower affinity for cAMP. At normal cellular cAMP levels this enzyme fails to phosphorylate one or more critical protein substrates; however, by raising internal cAMP levels, the defect can be overcome. Thus type I cAdPK seems to play an important role in the regulation of fibronectin mediated cell adhesion, cell aggregation, and endocytosis.

Differentiation of PC12 pheochromocytoma cells by sodium butyrate

PC12 pheochromocytoma cells cease dividing and show increased cell-cell and cell-substratum adhesion in response to treatment with sodium butyrate. These changes are accompanied by the rapid appearance of neuron-specific enolase, an APUD cell marker. However, neurofilament proteins, markers for neuronal differentiation, are not induced. These results suggest that sodium butyrate induces differentiation in the PC12 cell line, perhaps along the chromaffin cell pathway.

Phenotypic change from transformed to normal induced by benzoquinonoid ansamycins accompanies inactivation of p60src in rat kidney cells infected with Rous sarcoma virus

Three benzenoid ansamycin antibiotics (herbimycin, macbecin, and geldanamycin) were found to reduce the intracellular phosphorylation of p60src at a permissive temperature (33 degrees C) in a rat kidney cell line infected with a temperature-sensitive mutant of Rous sarcoma virus. This effect was accompanied by morphological changes from the transformed to the normal phenotype. The filamentous staining pattern of actin fibers was observed in the cells treated with these antibiotics at 33 degrees C. Removal of the antibiotics allowed the cells to revert to the transformed morphology. Ansamitocin, another benzenoid ansamycin, and naphthalenoid ansamycins such as streptovaricin and rifamycins did not show this effect. Pulse-labeling of the antibiotic-treated cultures with 32Pi showed a marked reduction of 32P radioactivity incorporated into p60src. A parallel experiment with [35S]methionine showed that synthesis of p60src was slightly inhibited. The immune complex prepared by mixing the herbimycin-treated cell extracts with antibody against p60src was inactive in vitro in phosphorylating the complex itself. On the contrary, the immune complex derived from untreated cells was active in vitro even in the presence of the antibiotics. These results suggest that benzoquinonoid ansamycins have no direct effect on src kinase but destroy its intracellular environment, resulting in an irreversible alteration of p60src and loss of catalytic activity.

Persistent infection with a nontransforming RNA virus leads to impaired growth factor receptors and response

The potential role of viral persistence with nontransforming viruses on cellular growth and cellular function has received little attention. We found that when infected with type 3 reovirus (five plaque-forming units (PFU/cell), balb/C 3T3 cells (a mouse embryo fibroblast cell line) undergo a limited lytic phase. The surviving cells, about 90% of the original cells, appear morphologically normal by light microscopy and exhibit normal growth patterns in serum-supplemented medium but are persistently infected by electron microscopy. These persistently infected cells shed infectious virus in the culture medium (1.6-60 X 10(6) PFU per 10(6) cells per 24 h). In comparison to control uninfected 3T3 cells, the persistently infected cells exhibit a 70-90% decrease in receptor number for epidermal growth factor (EGF). This occurs without production of any EGF-like material and is associated with a parallel decrease in EGF-stimulated DNA synthesis. By contrast, insulin receptors are increased in number three-fold and insulin and serum stimulated DNA synthesis are comparable to control uninfected cells. These results suggest that persistent infection with a nontransforming virus may lead to major alteration in control of cell growth by specific growth factors.

Increased level of cAMP-dependent protein kinase in aging human lung fibroblasts

Regulation of the expression of cAMP-dependent protein kinase in cellular aging was studied using the IMR-90 diploid human lung fibroblasts. The level of cAMP-dependent protein kinase present in cell extracts was monitored by 1) photoactivated incorporation of 8-N3-[32P]cAMP into the 47,000- and 54,000-dalton regulatory subunits of the type I and type II cAMP-dependent protein kinases, respectively; 2) cAMP-dependent phosphorylation of histone II AS catalyzed by the catalytic subunit of the kinase; and 3) fractionation and analysis of the type I and type II cAMP-dependent protein kinase by DEAE-Sephacel column chromatography. Our results showed an approximately two- to threefold increase in the level of the type I cAMP-dependent protein kinase and a somewhat smaller increase in the type II kinase in extracts of the "old" IMR-90 cells (population doubling greater than 48) as compared to that of the "young" cells (PDL 22-27). The timing of the increase in cAMP-dependent protein kinase coincided with a significant decrease in the proliferative potential of the cells. This result together with previously demonstrated effects of cAMP in the control of cell growth and differentiation and the increased expression of cAMP-dependent protein kinase during terminal differentiation of the murine preadipocytes (3T3-L1) and myoblast (L-5, L-6, and C2C13) suggests that regulation of the levels of cAMP and cAMP-dependent protein kinase plays a significant role in the control of cell growth and differentiation.

Phenotypic change from transformed to normal induced by benzoquinonoid ansamycins accompanies inactivation of p60src in rat kidney cells infected with Rous sarcoma virus

Three benzenoid ansamycin antibiotics (herbimycin, macbecin, and geldanamycin) were found to reduce the intracellular phosphorylation of p60src at a permissive temperature (33 degrees C) in a rat kidney cell line infected with a temperature-sensitive mutant of Rous sarcoma virus. This effect was accompanied by morphological changes from the transformed to the normal phenotype. The filamentous staining pattern of actin fibers was observed in the cells treated with these antibiotics at 33 degrees C. Removal of the antibiotics allowed the cells to revert to the transformed morphology. Ansamitocin, another benzenoid ansamycin, and naphthalenoid ansamycins such as streptovaricin and rifamycins did not show this effect. Pulse-labeling of the antibiotic-treated cultures with 32Pi showed a marked reduction of 32P radioactivity incorporated into p60src. A parallel experiment with [35S]methionine showed that synthesis of p60src was slightly inhibited. The immune complex prepared by mixing the herbimycin-treated cell extracts with antibody against p60src was inactive in vitro in phosphorylating the complex itself. On the contrary, the immune complex derived from untreated cells was active in vitro even in the presence of the antibiotics. These results suggest that benzoquinonoid ansamycins have no direct effect on src kinase but destroy its intracellular environment, resulting in an irreversible alteration of p60src and loss of catalytic activity.

Thyrotropin-induced formation of functional follicles in primary cultures of ovine thyroid cells

In primary cultures of ovine thyroid cells, TSH induced the expression of several differentiated functions including the formation of follicles, and synthesis and storage of iodinated thyroglobulin in the follicular lumen. In the present report, these follicles were shown by transmission (TEM) and scanning electron microscopy (SEM) to be intact, comprised of two or more cells and to possess numerous microvilli on the inner cell membranes facing the follicular lumen. The TSH-induced formation of follicles was reversible and dynamic, with the kinetics of formation preceding that of iodination. The follicles were further demonstrated to be functional in terms of thyroglobulin storage and iodination.

Effect of cholera toxin on the induction of gamma-glutamyl transpeptidase-positive clones by benzo(a)pyrene in embryonic mouse tongue cells in culture

The utility of gamma-glutamyl transpeptidase (GGT) as a histochemical marker to study the carcinogen-induced changes and its possible modulation by cholera toxin was explored in primary cell cultures. It was observed that cholera toxin not only promotes growth of fibroblasts in primary cell culture, but it also enhances the GGT-positive foci induced by benzo(a)pyrene. It is interesting to speculate that cholera toxin may be acting as a tumor promoter in primary cell cultures of embryonic mouse tongue.

Modulation of fibronectin gene activity in chick embryo fibroblasts transformed by a temperature-sensitive strain (ts68) of Rous sarcoma virus

Transcriptional regulation of the fibronectin gene is a major mechanism for lowering steady-state levels of fibronectin mRNA in chick embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSV) (1). In the present study, we have measured the change of transcriptional activity of the fibronectin gene in CEF transformed by a temperature-sensitive strain of RSV (ts68). Ts68-CEF maintained at either 35 degrees C or 41 degrees C were shifted to 41 degrees C or 35 degrees C, respectively, at 5-hour intervals, and isolated nuclei were used in runoff transcription assays. Nuclear RNA labeled with [alpha-32P]UTP was hybridized to DNA fragments encoding the src gene, the beta-actin gene and the fibronectin gene. In shift-up (35 degrees C----41 degrees C) and shift-down (41 degrees C----35 degrees C) experiments, src gene and beta-actin gene activities in ts68-CEF nuclei remained relatively unchanged. In ts68-CEF shifted to the nonpermissive temperature (41 degrees C), a lag time of at least 5 hours was followed by a 4- to 5-fold increase in fibronectin specific RNA 15 hours after the shift. When cells were shifted to the permissive temperature (35 degrees C), a 4- to 5-fold decrease in fibronectin RNA was apparent within 5 hours of the temperature shift and a 17- to 18-fold decrease was observed 15 hours after the shift. The relatively slow rates of changes of fibronectin gene activity in shift-up experiments suggest that the effect of p60src on fibronectin gene activity is indirect.

Translatable mRNA for GP140 (a subunit of type VI collagen) is absent in SV40 transformed fibroblasts

Production of GP140, a major component of the extracellular matrix of cultured fibroblasts, is markedly decreased in SV40 transformed cells as compared with normal cells (Carter, W. G., 1982, J. Biol. Chem., 257:13805-13815). To determine at what step the biosynthesis is inhibited, we compared the levels of functional mRNA for GP140 in normal and transformed fibroblasts. Translation of total RNA from W138 cells in a reticulocyte lysate, followed by immunoprecipitation with affinity-purified antibodies to GP140, yielded a single polypeptide with an Mr of 125,000. This polypeptide was identified as GP140 based on its immunoreactivity, collagenase sensitivity, and comigration on polyacrylamide gels with GP140 synthesized by cells in the presence of tunicamycin and 2,2'-bipyridyl. No cell-free synthesis of GP140 was observed with total RNA from SV40 transformed W138 cells, indicating that these cells contain very low levels of GP140-specific mRNA. The biosynthesis of GP140 might therefore be blocked at the transcriptional level.