Regulation of the mRNA for monocyte-derived neutrophil-activating peptide in differentiating HL60 promyelocytes

Chemokines and Their Receptors Are Key Players in the Orchestra That Regulates Wound Healing

SIGNIFICANCE

Normal wound healing progresses through a series of overlapping phases, all of which are coordinated and regulated by a variety of molecules, including chemokines. Because these regulatory molecules play roles during the various stages of healing, alterations in their presence or function can lead to dysregulation of the wound-healing process, potentially leading to the development of chronic, nonhealing wounds.

RECENT ADVANCES

A discovery that chemokines participate in a variety of disease conditions has propelled the study of these proteins to a level that potentially could lead to new avenues to treat disease. Their small size, exposed termini, and the fact that their only modifications are two disulfide bonds make them excellent targets for manipulation. In addition, because they bind to G-protein-coupled receptors (GPCRs), they are highly amenable to pharmacological modulation.

CRITICAL ISSUES

Chemokines are multifunctional, and in many situations, their functions are highly dependent on the microenvironment. Moreover, each specific chemokine can bind to several GPCRs to stimulate the function, and both can function as monomers, homodimers, heterodimers, and even oligomers. Activation of one receptor by any single chemokine can lead to desensitization of other chemokine receptors, or even other GPCRs in the same cell, with implications for how these proteins or their receptors could be used to manipulate function.

FUTURE DIRECTIONS

Investment in better understanding of the functions of chemokines and their receptors in a local context can reveal new ways for therapeutic intervention. Understanding how different chemokines can activate the same receptor and vice versa could identify new possibilities for drug development based on their heterotypic interactions.

A role for reactive oxygen species in endotoxin-induced elevation of MOR expression in the nervous and immune systems

This study examined the mechanism by which exposure to lipopolysaccharide (LPS) alters mu-opioid receptor (MOR) expression in immune and neuronal cells using an in vitro conditioned medium model system. We found that LPS stimulated the intracellular accumulation of reactive oxygen species (ROS) and MOR expression in macrophage-like TPA-HL-60 cells. Conditioned medium from the LPS-stimulated TPA-HL-60 cells increased MOR expression in SH-SY5Y cells, a neuronal cell model, through actions mediated by TNF-α and GM-CSF. These data suggest that the endotoxin, LPS, modulates MOR expression in nervous and immune cells via ROS signaling, and demonstrates the crosstalk that exists within the neuroimmune axis.

Gene mining: a novel and powerful ensemble decision approach to hunting for disease genes using microarray expression profiling

Current applications of microarrays focus on precise classification or discovery of biological types, for example tumor versus normal phenotypes in cancer research. Several challenging scientific tasks in the post-genomic epoch, like hunting for the genes underlying complex diseases from genome-wide gene expression profiles and thereby building the corresponding gene networks, are largely overlooked because of the lack of an efficient analysis approach. We have thus developed an innovative ensemble decision approach, which can efficiently perform multiple gene mining tasks. An application of this approach to analyze two publicly available data sets (colon data and leukemia data) identified 20 highly significant colon cancer genes and 23 highly significant molecular signatures for refining the acute leukemia phenotype, most of which have been verified either by biological experiments or by alternative analysis approaches. Furthermore, the globally optimal gene subsets identified by the novel approach have so far achieved the highest accuracy for classification of colon cancer tissue types. Establishment of this analysis strategy has offered the promise of advancing microarray technology as a means of deciphering the involved genetic complexities of complex diseases.

The 3'-untranslated region of human interleukin-8 mRNA suppresses IL-8 gene expression

Although adenosine/uridine (AU)-rich sequences in the 3'-untranslated region (UTR) of the interleukin-8 (IL-8) gene have been suggested to contribute to its post-transcriptional regulation, the molecular basis whereby this occurs still needs to be understood. To investigate the role of the 3'-UTR on human IL-8 gene regulation, chimeric reporter genes were generated by adding full length or differentially deleted 3'-UTR of the IL-8 gene to chloramphenicol acetyltransferase (CAT). Addition of the entire IL-8 3'-UTR markedly reduced CAT mRNA and protein expression in COS 7 cells. In a reporter gene study, IL-8 3'-UTR destabilized CAT mRNA, which was dependent on active transcription in COS 7 cells. A 357-base sequence (nucleotides (nt) 2387-2743 of genomic DNA) within 3'-UTR, designated e, suppressed CAT gene expression by accelerating CAT mRNA turnover. A 26-base AU-rich sequence (nt 2552-2577) within e, containing four AUUUA pentamers that form two UAUUUAUU and one UUAUUUAU octamers, did not suppress CAT gene expression. However, deletion of the AU-rich sequences attenuated the inhibitory effect of e on CAT gene expression. Elimination of the first 100 bases (nt 2386-2486) attenuated the potency of fragment e, but much weaker than elimination of the first 146 bases (nt 2387-2533). This study gives new insights in unravelling the molecular mechanisms involved in the post-transcriptional regulation of the IL-8 gene.

Cell cycle regulation of human interleukin-8 gene expression by the human immunodeficiency virus type 1 Tat protein

The human immunodeficiency virus type 1 (HIV-1) Tat protein has been reported to transactivate several cellular genes, including the potent chemotactic factor interleukin-8 (IL-8). Consistent with these in vitro assays, elevated levels of IL-8 protein are found in the serum of HIV-infected individuals. We now extend these observations by demonstrating that Tat induction of IL-8 is linked to the cell cycle. Cells that constitutively express the Tat(1-86) protein (eTat) and control cells (pCEP) were reversibly blocked at the G(1)/S border with hydroxyurea or thymidine. The cells were subsequently released, and IL-8 expression was monitored by RNase protection assays and enzyme-linked immunosorbent assay (ELISA). RNase protection assays demonstrated that IL-8 mRNA expression is transiently induced, approximately fourfold, as the Tat-expressing cells enter S phase. Consistent with the RNase protection assay, an increase in IL-8 protein was observed in the cell supernatant using an IL-8 ELISA. Similar experiments were performed following a reversible block at the G(2)/M border with nocodazole and release into G(1). Using the RNase protection assay and ELISA, little or no increase in IL-8 expression was observed during G(1). Using gel shift as well as an immobilized DNA binding assay, we demonstrate that the increase in IL-8 gene expression correlates with a specific increase in p65 NF-kappa B binding activity only in the nucleus of the Tat-expressing cells. Moreover, the CREB-binding protein coactivator is present in the complex in the Tat cell line. Finally, we demonstrate that the presence of the proteasome inhibitor MG-132 inhibits the induction of NF-kappa B binding, as well as IL-8 expression, supporting the role of NF-kappa B.

Variegated expression of the endogenous immunoglobulin heavy-chain gene in the absence of the intronic locus control region

The expression of chromosomally integrated transgenes usually varies greatly among independent transfectants. This variability in transgene expression has led to the definition of locus control regions (LCRs) as elements which render expression consistent. Analyses of expression in single cells revealed that the expression of transgenes which lack an LCR is often variegated, i.e., on in some cells and off in others. In many cases, transgenes which show variegated expression were found to have inserted near the centromere. These observations have suggested that the LCR prevents variegation by blocking the inhibitory effect of heterochromatin and other repetitive-DNA-containing structures at the insertion site and have raised the question of whether the LCR plays a similar role in endogenous genes. To address this question, we have examined the effects of deleting the LCR from the immunoglobulin heavy-chain locus of a mouse hybridoma cell line in which expression of the immunoglobulin mu heavy-chain gene is normally highly stable. Our analysis of mu expression in single cells shows that deletion of this LCR resulted in variegated expression of the mu gene. That is, in the absence of the LCR, expression of the mu gene in the recombinant locus could be found in either of two epigenetically maintained, metastable states, in which transcription occurred either at the normal rate or not at all. In the absence of the LCR, the on state had a half-life of approximately 100 cell divisions, while the half-life of the off state was approximately 40,000 cell divisions. For recombinants with an intact LCR, the half-life of the on state exceeded 50,000 cell divisions. Our results thus indicate that the LCR increased the stability of the on state by at least 500-fold.

Induction of interleukin-8 synthesis integrates effects on transcription and mRNA degradation from at least three different cytokine- or stress-activated signal transduction pathways

A hallmark of inflammation is the burst-like formation of certain proteins, initiated by cellular stress and proinflammatory cytokines like interleukin 1 (IL-1) and tumor necrosis factor, stimuli which simultaneously activate different mitogen-activated protein (MAP) kinases and NF-kappaB. Cooperation of these signaling pathways to induce formation of IL-8, a prototype chemokine which causes leukocyte migration and activation, was investigated by expressing active and inactive forms of protein kinases. Constitutively active MAP kinase kinase 7 (MKK7), an activator of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) pathway, induced IL-8 synthesis and transcription from a minimal IL-8 promoter. Furthermore, MKK7 synergized in both effects with NF-kappaB-inducing kinase (NIK). Activation of the IL-8 promoter by either of the kinases required functional NF-kappaB and AP-1 sites. While NIK and MKK7 did not affect degradation of IL-8 mRNA, an active form of MKK6, which selectively activates p38 MAP kinase, induced marked stabilization of the transcript and further increased IL-8 protein formation induced by NIK plus MKK7. Consistently, the MAP kinase kinase kinase MEKK1, which can activate NF-kappaB, SAPK/JNK, and p38 MAP kinases, most potently induced IL-8 formation. These results provide evidence that maximal IL-8 gene expression requires the coordinate action of at least three different signal transduction pathways which cooperate to induce mRNA synthesis and suppress mRNA degradation.

Superinduction of IL-8 in T Cells by HIV-1 Tat Protein Is Mediated Through NF-κB Factors

Elevated levels of circulating IL-8, a potent chemotactic factor for granulocytes and T lymphocytes, are found in HIV-infected individuals. The HIV-1 transactivator protein Tat increased IL-8 secretion in T cell lines following CD3- and CD28-mediated costimulation. Full-length Tat (Tat101) enhanced IL-8 transcription through up-regulated transcription factor binding to the CD28-responsive element (CD28RE) in the IL-8 promoter. Expression of the Tat splice variant Tat72 (72 amino acids) also enhanced IL-8 production following T cell stimulation via a different, most likely post-transcriptional, mechanism. The CD28RE in the IL-8 promoter was characterized as a low-affinity NF-κB binding site recognized by the transcription factors p50 (NF-κB1), p65 (RelA) and c-rel. Transcription factor binding to “classical” NF-κB sites in the HIV-1, the human IL-2, and lymphotoxin promoters, recognized by p50 and p65 following CD3+28-mediated costimulation, was unaffected by Tat101 as was binding to the AP-1 motif in the IL-8 promoter. These experiments identify the CD28RE in the IL-8 promoter as a c-rel recognition site and a Tat101-responsive element. The effect of Tat101 on CD28REs in the IL-8 promoter and the subsequent up-regulation of IL-8 secretion is likely to contribute to the immune dysregulation observed during HIV-1 infection.

Expression of the (recombinant) endogenous immunoglobulin heavy-chain locus requires the intronic matrix attachment regions

The elements which regulate gene expression have traditionally been identified by their effects on reporter genes which have been transfected into cell lines or animals. It is generally assumed that these elements have a comparable role in expression of the corresponding endogenous locus. Nevertheless, several studies of immunoglobulin heavy-chain (IgH) gene expression have reported that the requirements for expressing IgH-derived transgenes differ from the requirements for expression of the endogenous IgH locus. Thus, although expression of transgenes requires multiple elements from the J(H)-C mu intron--the E mu core enhancer, the matrix attachment regions (MARs) which flank E mu, and several switch-associated elements--B-cell lines in which expression of the endogenous heavy-chain gene is maintained at the normal level in the absence of these intronic elements have occasionally been reported. Gene targeting offers an alternative method for assessing regulatory elements, one in which the role of defined segments of endogenous genes can be evaluated in situ. We have applied this approach to the IgH locus of a hybridoma cell line, generating recombinants which bear predetermined modifications in the functional, endogenous mu heavy-chain gene. Our analysis indicates the following. (i) Ninety-eight percent of the expression of the recombinant endogenous mu gene depends on elements in the MAR-E mu-MAR segment. (ii) Expression of the recombinant mu gene depends strongly on the MARs of the J(H)-C mu intron but not on the adjoining E mu core enhancer and switch regions; because our recombinant cell lines bear only a single copy of the mu gene, our results indicate that mu expression is activated by MAR elements lying within that same mu transcription unit. (iii) The MAR segment includes at least one activating element in addition to those defined previously by the binding of presumptive activating proteins in the nuclear matrix. (iv) Close association of the MARs with the E mu enhancer is not required for MAR-stimulated expression. (v) The other MARs in the IgH locus do not in their normal context provide the requisite MAR function.

Thrombin stimulates production of interleukin-8 in human umbilical vein endothelial cells

Interleukin-8 (IL-8) is regarded as an important mediator of inflammation because of its potent and specific chemotactic activity on neutrophils. In the present investigation, human umbilical vein endothelial cells (HUVEC) stimulated with thrombin were found to produce IL-8, in a dose- and time-dependent manner. After stimulation with 10 U/ml thrombin for 24 hr, the level of IL-8 in the conditioned medium was 14 ng/ml, or enough to elicit PMN chemotaxis in vitro. Northern blot analysis revealed that thrombin as well as IL-1 beta elevates the level of IL-8 mRNA preceding the formation of IL-8 protein. A synthetic peptide SFLLRN [human thrombin receptor-activating peptide (TRAP)] was found to mimic the action of thrombin. Preincubation with anti-thrombin compounds such as hirudin and antithrombin-III-heparin almost completely suppressed the action of thrombin without affecting the actions of other stimuli including IL-1 beta, phorbol 12-myristate 13-acetate (PMA) and TRAP. Diisopropylfluorophosphate-treated thrombin did not stimulate IL-8 production. Calphostin-C, a protein kinase C (PKC) inhibitor, attenuated the production of IL-8 by thrombin, TRAP and PMA, but left the action of IL-1 beta unchanged. These results strongly suggest that catalytic activation of thrombin receptor by thrombin results in PKC-dependent IL-8 production accompanied by an increase in IL-8 mRNA level.

Lipopolysaccharide-induced interleukin-8 gene expression in human granulocytes: transcriptional inhibition by interferon-gamma

We recently showed that lipopolysaccharide (LPS) is a potent inducer of interleukin-8 (IL-8) expression in human polymorphonuclear leucocytes (PMN), at the level of both mRNA and protein, and that interferon-gamma (IFN gamma) inhibits IL-8 mRNA accumulation in stimulated PMN. To further define the molecular basis of the regulation of IL-8 gene expression in PMN, we investigated the effects of LPS and IFN gamma at both the transcriptional and post-transcriptional levels. As determined by Northern blot analysis, new protein synthesis was not required for the induction of IL-8 mRNA expression by LPS. Neither did the half-life of IL-8 mRNA in LPS-treated PMN differ from that observed in untreated cells. However, nuclear run-on analysis revealed that LPS increased the transcription of the IL-8 and IL-1 beta genes and that, in LPS-activated cells, IFN gamma markedly inhibited the rate of IL-8 gene transcription, but not that of IL-1 beta. IFN gamma did not affect IL-8 mRNA stability in LPS-treated PMN, indicating that the cytokine does not regulate LPS-induced IL-8 gene expression through post-transcriptional events. These results provide the first evidence that human granulocytes can actively transcribe the IL-8 gene, and that transcriptional inhibition is the mechanism by which IFN gamma inhibits IL-8 gene expression in PMN.

Posttranscriptional stabilization underlies p53-independent induction of p21WAF1/CIP1/SDI1 in differentiating human leukemic cells

p21WAF/CIP1/SDI1 is a recently identified gene expressed in cells harboring wild-type but not mutant p53 gene. It encodes a nuclear protein of 21 kD which inhibits cyclin-dependent kinase activity. Constitutive p21WAF1/CIP1/SDI1 mRNA expression was detected in neoplastic cells from patients with various hematological malignancies as well as in normal bone marrow mononuclear cells and in myeloid and lymphoid cell lines independent of their p53 status. Induced differentiation of the p53-deficient promyelocytic HL-60 cells along the monocytic lineage by phorbol ester or 1a,25 dihydroxyvitamin D3 resulted in a marked increase of both p21WAF1/CIP1/SDI1 mRNA and protein expression due to enhanced mRNA stability. Differentiation towards the granulocytic lineage by all-trans retinoic acid or dimethylsulfoxide failed to produce this effect. p21WAF1/CIP1/SDI1 is an immediate early gene since its upregulation occurred independently of de novo protein synthesis. The induction of p21WAF1/CIP1/SDI1 expression and its regulation in p53-deficient differentiating leukemic cells support the idea of an additional, p53-independent role of p21WAF1/CIP1/SDI1 in human hematopoiesis.

Interleukin-8 gene induction in the myocardium after ischemia and reperfusion in vivo

Neutrophil adhesion and direct cytotoxicity for cardiac myocytes require chemotactic stimulation and are dependent upon CD18-ICAM-1 binding. To characterize the potential role of IL-8 in this interaction, canine IL-8 cDNA was cloned and the mature recombinant protein expressed in Escherichia coli BL21 cells. Recombinant canine IL-8 markedly increased adhesion of neutrophils to isolated canine cardiac myocytes. This adhesion resulted in direct cytotoxicity for cardiac myocytes. Both processes were specifically blocked by antibodies directed against CD18 and IL-8. In vivo, after 1 h of coronary occlusion, IL-8 mRNA was markedly and consistently induced in reperfused segments of myocardium. IL-8 mRNA was not induced in control (normally perfused) myocardial segments. Minimal amounts of IL-8 mRNA were detected after 3 or 4 h of ischemia without reperfusion. Highest levels of induction were evident in the most ischemic myocardial segments. IL-8 mRNA peaked in the first 3 h of reperfusion and persisted at high levels beyond 24 h. IL-8 staining was present in the inflammatory infiltrate near the border between necrotic and viable myocardium, as well as in small veins in the same area. These findings provide the first direct evidence for regulation of IL-8 in ischemic and reperfused canine myocardium and support the hypothesis that IL-8 participates in neutrophil-mediated myocardial injury.

AUUUA is not sufficient to promote poly(A) shortening and degradation of an mRNA: the functional sequence within AU-rich elements may be UUAUUUA(U/A)(U/A)

AU-rich elements (AREs) in the 3' untranslated regions of several cytokine and oncogene mRNAs have been shown to function as signals for rapid mRNA degradation, and it is assumed that the many other cytokine and oncogene mRNAs that contain AU-rich sequences in the 3' untranslated region are similarly targeted for rapid turnover. We have used a chimeric gene composed mostly of growth hormone sequences with expression driven by the c-fos promoter to investigate the minimal sequence required to act as a functional destabilizing element and to monitor the effect of these sequences on early steps in the degradation pathway. We find that neither AUUUA, UAUUUA, nor AUUUAU can function as a destabilizing element. However, the sequence UAUUUAU, when present in three copies, is sufficient to destabilize a chimeric mRNA. We propose that this sequence functions by virtue of being a sufficient portion of the larger sequence, UUAUUUA(U/A)(U/A), that we propose forms the optimal binding site for a destabilizing factor. The destabilizing effect depends on the number of copies of this proposed binding site and their degree of mismatch in the first two and last two positions, with mismatches in the AUUUA sequence not being tolerated. We found a strict correlation between the effect of an ARE on degradation rate and the effect on the rate of poly(A) shortening, consistent with deadenylation being the first and rate-limiting step in degradation, and the step stimulated by destabilizing AREs. Deadenylation was observed to occur in at least two phases, with an oligo(A) intermediate transiently accumulating, consistent with the suggestion that the degradation processes may be similar in yeast and mammalian cells. AREs that are especially U rich and contain no UUAUUUA(U/A)(U/A) motifs failed to influence the degradation rate or the deadenylation rate, either when downstream of suboptimal destabilizing AREs or when alone.

AUUUA is not sufficient to promote poly(A) shortening and degradation of an mRNA: the functional sequence within AU-rich elements may be UUAUUUA(U/A)(U/A)

AU-rich elements (AREs) in the 3' untranslated regions of several cytokine and oncogene mRNAs have been shown to function as signals for rapid mRNA degradation, and it is assumed that the many other cytokine and oncogene mRNAs that contain AU-rich sequences in the 3' untranslated region are similarly targeted for rapid turnover. We have used a chimeric gene composed mostly of growth hormone sequences with expression driven by the c-fos promoter to investigate the minimal sequence required to act as a functional destabilizing element and to monitor the effect of these sequences on early steps in the degradation pathway. We find that neither AUUUA, UAUUUA, nor AUUUAU can function as a destabilizing element. However, the sequence UAUUUAU, when present in three copies, is sufficient to destabilize a chimeric mRNA. We propose that this sequence functions by virtue of being a sufficient portion of the larger sequence, UUAUUUA(U/A)(U/A), that we propose forms the optimal binding site for a destabilizing factor. The destabilizing effect depends on the number of copies of this proposed binding site and their degree of mismatch in the first two and last two positions, with mismatches in the AUUUA sequence not being tolerated. We found a strict correlation between the effect of an ARE on degradation rate and the effect on the rate of poly(A) shortening, consistent with deadenylation being the first and rate-limiting step in degradation, and the step stimulated by destabilizing AREs. Deadenylation was observed to occur in at least two phases, with an oligo(A) intermediate transiently accumulating, consistent with the suggestion that the degradation processes may be similar in yeast and mammalian cells. AREs that are especially U rich and contain no UUAUUUA(U/A)(U/A) motifs failed to influence the degradation rate or the deadenylation rate, either when downstream of suboptimal destabilizing AREs or when alone.

MGSA/GRO transcription is differentially regulated in normal retinal pigment epithelial and melanoma cells

We have characterized constitutive and cytokine-regulated MGSA/GRO alpha, -beta, and -gamma gene expression in normal retinal pigment epithelial (RPE) cells and a malignant melanoma cell line (Hs294T) to discern the mechanism for MGSA/GRO constitutive expression in melanoma. In RPE cells, constitutive MGSA/GRO alpha, -beta, and -gamma mRNAs are not detected by Northern (RNA) blot analysis although nuclear runoff experiments show that all three genes are transcribed. In Hs294T cells, constitutive MGSA/GRO alpha expression is detectable by Northern blot analysis, and the level of basal MGSA/GRO alpha transcription is 8- to 30-fold higher than in RPE cells. In contrast, in Hs294T cells, basal MGSA/GRO beta and -gamma transcription is only twofold higher than in RPE cells and no beta or gamma mRNA is detected by Northern blot. These data suggest that the constitutive MGSA/GRO alpha mRNA in Hs294T cells is due to increased basal MGSA/GRO alpha gene transcription. The cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) significantly increase the mRNA levels for all three MGSA/GRO isoforms in Hs294T and RPE cells, and both transcriptional and posttranscriptional mechanisms are operational. Nuclear runoff assays indicate that in RPE cells, a 1-h IL-1 treatment induces a 10- to 20-fold increase in transcription of MGSA/GRO alpha, -beta and -gamma but only a 2-fold increase in Hs294T cells. Similarly, chloramphenicol acetyltransferase (CAT) reporter gene analysis using the MGSA/GRO alpha, -beta, and -gamma promoter regions demonstrates that IL-1 treatment induces an 8- to 14-fold increase in CAT activity in RPE cells but only a 2-fold increase in Hs294T cells. The effect of deletion or mutation of the MGSA/GRO alpha NF-kappa B element, combined with data from gel mobility shift analyses, indicates that the NF-kappa B p50/p65 heterodimer in RPE cells plays an important role in IL-1- and TNF alpha-enhanced gene transcription. In Hs294T cells, gel shift analyses indicate that IL-1 and TNF alpha induce NF-kappa B complex formation; however, transactivation does not occur, suggesting that subtle differences in the NF-kappa B complexes may result in the inability of the cytokines IL-1 and TNF alpha to activate transcription of the MGSA/GRO genes. IL-1 and TNF alpha posttranscriptionally regulate MGSA/GRO mRNA levels in both cell types. In Hs294T cells, IL-1 increases the half-life of MGSA/GRO alpha from 15 min to 6 h (a 24-fold increase in half-life). These data indicate that IL-1 and TNF alpha transcriptionally and posttranscriptionally regulate MGSA/GRO alpha, -beta, and -gamma mRNA levels in RPE cells, while in Hs294T cells, the major effect of IL-1 and TNF alpha is on mRNA stability.

MGSA/GRO transcription is differentially regulated in normal retinal pigment epithelial and melanoma cells

We have characterized constitutive and cytokine-regulated MGSA/GRO alpha, -beta, and -gamma gene expression in normal retinal pigment epithelial (RPE) cells and a malignant melanoma cell line (Hs294T) to discern the mechanism for MGSA/GRO constitutive expression in melanoma. In RPE cells, constitutive MGSA/GRO alpha, -beta, and -gamma mRNAs are not detected by Northern (RNA) blot analysis although nuclear runoff experiments show that all three genes are transcribed. In Hs294T cells, constitutive MGSA/GRO alpha expression is detectable by Northern blot analysis, and the level of basal MGSA/GRO alpha transcription is 8- to 30-fold higher than in RPE cells. In contrast, in Hs294T cells, basal MGSA/GRO beta and -gamma transcription is only twofold higher than in RPE cells and no beta or gamma mRNA is detected by Northern blot. These data suggest that the constitutive MGSA/GRO alpha mRNA in Hs294T cells is due to increased basal MGSA/GRO alpha gene transcription. The cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) significantly increase the mRNA levels for all three MGSA/GRO isoforms in Hs294T and RPE cells, and both transcriptional and posttranscriptional mechanisms are operational. Nuclear runoff assays indicate that in RPE cells, a 1-h IL-1 treatment induces a 10- to 20-fold increase in transcription of MGSA/GRO alpha, -beta and -gamma but only a 2-fold increase in Hs294T cells. Similarly, chloramphenicol acetyltransferase (CAT) reporter gene analysis using the MGSA/GRO alpha, -beta, and -gamma promoter regions demonstrates that IL-1 treatment induces an 8- to 14-fold increase in CAT activity in RPE cells but only a 2-fold increase in Hs294T cells. The effect of deletion or mutation of the MGSA/GRO alpha NF-kappa B element, combined with data from gel mobility shift analyses, indicates that the NF-kappa B p50/p65 heterodimer in RPE cells plays an important role in IL-1- and TNF alpha-enhanced gene transcription. In Hs294T cells, gel shift analyses indicate that IL-1 and TNF alpha induce NF-kappa B complex formation; however, transactivation does not occur, suggesting that subtle differences in the NF-kappa B complexes may result in the inability of the cytokines IL-1 and TNF alpha to activate transcription of the MGSA/GRO genes. IL-1 and TNF alpha posttranscriptionally regulate MGSA/GRO mRNA levels in both cell types. In Hs294T cells, IL-1 increases the half-life of MGSA/GRO alpha from 15 min to 6 h (a 24-fold increase in half-life). These data indicate that IL-1 and TNF alpha transcriptionally and posttranscriptionally regulate MGSA/GRO alpha, -beta, and -gamma mRNA levels in RPE cells, while in Hs294T cells, the major effect of IL-1 and TNF alpha is on mRNA stability.

Transcriptional activation of the CEF-4/9E3 cytokine gene by pp60v-src

The CEF-4/9E3 gene is expressed constitutively in Rous sarcoma virus (RSV)-transformed cells. This expression is largely determined by an increase in transcription of the gene. In this report, we characterize the regulatory elements responsible for the transformation-dependent activation of CEF-4/9E3. Three sequences corresponding to AP-1, PRD II/kappa B, and TAACGCAATT are involved in the process and therefore define the src-responsive unit (SRU) of the CEF-4 promoter. In constructs containing a deletion of the SRU, multiple copies of AP-1 or PRD II/kappa B, but not TAACGCAATT, led to activation of the promoter. Thus, factors interacting with these elements are constitutively activated in RSV-transformed chicken embryo fibroblasts. In agreement with the results of transient expression assays, protein binding to AP-1, PRD II/kappa B, and TAACGCAATT were more abundant in the nuclei of transformed cells. The expression of the CEF-4 promoter was investigated in cells infected by a temperature-sensitive mutant of RSV. No significant increase in CEF-4 promoter activity was detected early after activation of pp60v-src. In contrast, a substantial activation of the CEF-4 promoter was detected late after a temperature shift. Factors interacting with the TAACGCAATT, PRD II/kappa B, and AP-1 elements accumulated gradually over a period of several hours. Therefore, transcriptional activation plays an important role in the late, constitutive expression of the CEF-4 gene in stably transformed cells.

Transcriptional activation of the CEF-4/9E3 cytokine gene by pp60v-src

The CEF-4/9E3 gene is expressed constitutively in Rous sarcoma virus (RSV)-transformed cells. This expression is largely determined by an increase in transcription of the gene. In this report, we characterize the regulatory elements responsible for the transformation-dependent activation of CEF-4/9E3. Three sequences corresponding to AP-1, PRD II/kappa B, and TAACGCAATT are involved in the process and therefore define the src-responsive unit (SRU) of the CEF-4 promoter. In constructs containing a deletion of the SRU, multiple copies of AP-1 or PRD II/kappa B, but not TAACGCAATT, led to activation of the promoter. Thus, factors interacting with these elements are constitutively activated in RSV-transformed chicken embryo fibroblasts. In agreement with the results of transient expression assays, protein binding to AP-1, PRD II/kappa B, and TAACGCAATT were more abundant in the nuclei of transformed cells. The expression of the CEF-4 promoter was investigated in cells infected by a temperature-sensitive mutant of RSV. No significant increase in CEF-4 promoter activity was detected early after activation of pp60v-src. In contrast, a substantial activation of the CEF-4 promoter was detected late after a temperature shift. Factors interacting with the TAACGCAATT, PRD II/kappa B, and AP-1 elements accumulated gradually over a period of several hours. Therefore, transcriptional activation plays an important role in the late, constitutive expression of the CEF-4 gene in stably transformed cells.

Removal of a 3' non-coding sequence is an initial step in degradation of gro alpha mRNA and is regulated by interleukin-1

I have previously shown that IL-1 regulates the stability of gro alpha mRNA in fibroblasts and that decay is associated with appearance of a smaller species of gro RNA that lacks poly(A). In this study, the relationship between the two species of gro RNA, which migrate at 1.3 and 0.9 kilobases, was characterized. Following withdrawal of IL-1 or addition of IL-1 receptor antagonist, 1.3 kilobase gro alpha mRNA was rapidly degraded and this was associated with increased expression of the 0.9 kilobase RNA. This increase occurred in the presence of actinomycin D, indicating that the 0.9 kilobase gro RNA was a product of a pre-existing transcript. In cells treated with 1 pg/ml IL-1, both species were induced but the 0.9 kilobase RNA appeared later, consistent with a precursor-product relationship. In cells treated with higher doses of IL-1, the 0.9 kilobase RNA was not expressed. Using an RNAase protection assay, the 0.9 kilobase poly(A)-minus gro RNA was found to be derived from gro alpha mRNA by removal of a 130-nucleotide sequence from the 3' non-coding region. This is one of few examples of formation of an mRNA decay intermediate in vivo; it indicates that degradation of the body of gro alpha mRNA is initiated by site-specific nuclease attack. Characterization of the mechanism of gro alpha mRNA degradation is a first step towards identification of the ribonuclease that controls gro alpha mRNA stability.

Stability of maternal mRNA in Xenopus embryos: role of transcription and translation

The first 12 cell divisions of Xenopus laevis embryos do not require gene transcription. This means that the regulation of gene expression during this period is controlled at post transcriptional levels and makes Xenopus early development a potentially interesting biological system with which to study the mechanisms involved. We describe here the stability characteristics of several maternal Xenopus mRNAs which are deadenylated soon after fertilisation (J. Paris and M. Philippe, Dev. Biol., in press). We show that these mRNAs were only degraded in the embryo after the midblastula transition (MBT), when gene transcription was initiated. The kinetics with which the deadenylated maternal mRNAs decreased in the post-MBT embryos showed sequence specificity. The degradation of these mRNAs after the MBT was inhibited by cycloheximide but was not affected by dactinomycin. Therefore, the destabilization of these mRNAs does not appear to be initiated by new embryonic gene transcripts. Sequence comparisons of the 3' untranslated region of these mRNAs identified several motifs which may be involved in the posttranscriptional control of these gene products.

Stability of maternal mRNA in Xenopus embryos: role of transcription and translation

The first 12 cell divisions of Xenopus laevis embryos do not require gene transcription. This means that the regulation of gene expression during this period is controlled at post transcriptional levels and makes Xenopus early development a potentially interesting biological system with which to study the mechanisms involved. We describe here the stability characteristics of several maternal Xenopus mRNAs which are deadenylated soon after fertilisation (J. Paris and M. Philippe, Dev. Biol., in press). We show that these mRNAs were only degraded in the embryo after the midblastula transition (MBT), when gene transcription was initiated. The kinetics with which the deadenylated maternal mRNAs decreased in the post-MBT embryos showed sequence specificity. The degradation of these mRNAs after the MBT was inhibited by cycloheximide but was not affected by dactinomycin. Therefore, the destabilization of these mRNAs does not appear to be initiated by new embryonic gene transcripts. Sequence comparisons of the 3' untranslated region of these mRNAs identified several motifs which may be involved in the posttranscriptional control of these gene products.

Processing of 9E3 mRNA and regulation of its stability in normal and Rous sarcoma virus-transformed cells

We studied the expression of 9E3 mRNA, which is known to be induced in chicken embryo fibroblasts by p60v-src activity and by serum. In addition to full-length 9E3 mRNA, we identified several smaller RNAs that hybridized with 9E3 cDNA. One of these RNAs hybridized with a 5' 9E3 cDNA probe but not with a 3' cDNA probe. The other hybridized with a 3' cDNA probe but lacked 5' sequences, including the entire 9E3 coding region. Only the latter RNA was polyadenylylated, as determined by RNase H digestion in the presence of oligo(dT). The level of the small RNAs increased after treatment with cycloheximide and actinomycin D, indicating that the small RNAs were produced by processing of preexisting transcripts. The derivation of the small RNAs from 9E3 mRNA rather than from a related gene was confirmed by S1 nuclease analysis. The 3' terminus of the 5' RNA and the 5' terminus of the 3' RNA mapped to the same position, which suggested that the small RNAs were formed by endonucleolytic cleavage of 9E3 mRNA at a specific site in the 3' noncoding region. We also found that the stability of 9E3 mRNA was increased after serum stimulation and was greater in Rous sarcoma virus-transformed than in uninfected cells. The relative amount of the small RNAs as compared with the full-length transcript was greatest under conditions in which the full-length transcript was least stable. These data suggest that site-specific endonucleolytic cleavage regulates the stability of 9E3 mRNA.

Processing of 9E3 mRNA and regulation of its stability in normal and Rous sarcoma virus-transformed cells

We studied the expression of 9E3 mRNA, which is known to be induced in chicken embryo fibroblasts by p60v-src activity and by serum. In addition to full-length 9E3 mRNA, we identified several smaller RNAs that hybridized with 9E3 cDNA. One of these RNAs hybridized with a 5' 9E3 cDNA probe but not with a 3' cDNA probe. The other hybridized with a 3' cDNA probe but lacked 5' sequences, including the entire 9E3 coding region. Only the latter RNA was polyadenylylated, as determined by RNase H digestion in the presence of oligo(dT). The level of the small RNAs increased after treatment with cycloheximide and actinomycin D, indicating that the small RNAs were produced by processing of preexisting transcripts. The derivation of the small RNAs from 9E3 mRNA rather than from a related gene was confirmed by S1 nuclease analysis. The 3' terminus of the 5' RNA and the 5' terminus of the 3' RNA mapped to the same position, which suggested that the small RNAs were formed by endonucleolytic cleavage of 9E3 mRNA at a specific site in the 3' noncoding region. We also found that the stability of 9E3 mRNA was increased after serum stimulation and was greater in Rous sarcoma virus-transformed than in uninfected cells. The relative amount of the small RNAs as compared with the full-length transcript was greatest under conditions in which the full-length transcript was least stable. These data suggest that site-specific endonucleolytic cleavage regulates the stability of 9E3 mRNA.