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PubMed1992

Differential expression of early response genes, c-jun, c-fos, and jun B, in A5 cells.

We examined the expression of c-fos, c-jun, and jun B after activation of different signal transduction pathways in the A5 rat salivary epithelial cell line. Stimulation of beta-adrenergic receptors by isoproterenol, or addition of 8-bromoadenosine 3',5'-cyclic monophosphate, induces the expression of c-fos and jun B by a protein kinase A-mediated pathway. Phorbol 12-myristate 13-acetate (PMA) induces the expression of all three genes, but with different kinetics. While c-fos and jun B mRNA levels increase early (1 h) after stimulation and transiently, those of c-jun remain higher than control even after stimulation for 8 h and return to basal levels by 24 h. Inhibitors of protein kinase C block the effect of PMA on c-fos, c-jun, and jun B expression, indicating that these genes are also regulated by a protein kinase C-mediated mechanism in A5 cells. Increases in cytosolic Ca2+ by A23187 or ionomycin induce only the expression of c-fos gene. This induction is abolished when A5 cells are loaded with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid before treatment with the ionophores, or when serum is excluded from the incubation medium. Exclusion of serum from the medium does not change the effects of isoproterenol or PMA on c-fos, c-jun, or jun B. These results strongly suggest that serum factors act synergistically with Ca2+ to induce c-fos expression in A5 cells. The studies presented here indicate that different signal transduction pathways operate in A5 cells for the induction of c-fos, c-jun, and jun B genes.

Animals↗

PubMed1990

Multiple adenosine 3',5'-cyclic [corrected] monophosphate response element DNA-binding proteins generated by gene diversification and alternative exon splicing.

The protein sequence deduced from the open reading frame of a human placental cDNA encoding a cAMP-responsive enhancer (CRE)-binding protein (CREB-327) has structural features characteristic of several other transcriptional transactivator proteins including jun, fos, C/EBP, myc, and CRE-BP1. Results of Southwestern analysis of nuclear extracts from several different cell lines show that there are multiple CRE-binding proteins, which vary in size in cell lines derived from different tissues and animal species. To examine the molecular diversity of CREB-327 and related proteins at the nucleic acid level, we used labeled cDNAs from human placenta that encode two different CRE-binding proteins (CREB-327 and CRE-BP1) to probe Northern and Southern blots. Both probes hybridized to multiple fragments on Southern blots of genomic DNA from various species. Alternatively, when a human placental c-jun probe was hybridized to the same blot, a single fragment was detected in most cases, consistent with the intronless nature of the human c-jun gene. The CREB-327 probe hybridized to multiple mRNAs, derived from human placenta, ranging in size from 2-9 kilobases. In contrast, the CRE-BP1 probe identified a single 4-kilobase mRNA. Sequence analyses of several overlapping human genomic cosmid clones containing CREB-327 sequences in conjunction with polymerase chain reaction indicates that the CREB-327/341 cDNAs are composed of at least eight or nine exons, and analyses of human placental cDNAs provide direct evidence for at least one alternatively spliced exon. Analyses of mouse/hamster-human hybridoma DNAs by Southern blotting and polymerase chain reaction localizes the CREB-327/341 gene to human chromosome 2. The results indicate that there is a dichotomy of CREB-like proteins, those that are related by overall structure and DNA-binding specificity as well as those that are related by close similarities of primary sequences.

Amino Acid Sequence↗

PubMed1990

Differential effects of the adenovirus E1A oncogene on members of the AP-1 transcription factor family.

The adenovirus early region 1A (E1A) oncogene interferes with the expression level and activity of the AP-1 transcription factor family. E1A abolished the transactivating function of AP-1 (Jun/Fos), which binds to the 12-O-tetradecanoylphorbol-13-acetate-responsive element of the collagenase gene (collTRE). In contrast, the activity of another member of the AP-1 family that binds to the c-junTRE was not repressed. The mRNA expression of the c-jun gene was, in fact, strongly elevated in various cell types expressing the E1A gene of either adenovirus type 5 (Ad5) or Ad12. The regulation of the junB gene by adenovirus E1A, on the other hand, depended both on the cell type and on the transforming adenovirus serotype. The fact that E1A-induced alterations in the repertoire of AP-1 transcription factors depend on its transforming domain in conserved region 1 suggests that the effects are relevant for the transformation process.

Adenovirus Early Proteins↗

PubMed2002

Comparison of gene expression patterns and migration capability at quiescent and proliferating vascular smooth muscle cells stimulated by cytokines.

The changes of the gene expression patterns and the migration capability of vascular smooth muscle cells (VSMC) at the quiescent and proliferating states were investigated after VSMC was stimulated by cytokines. VSMC migration was measured using a model of wounding injury of confluent cultured cells and a Boyden chamber assay. The migration distance of the quiescent VSMC induced by cytokines bFGF, IL-1beta and TNF-alpha was 5.8, 4.7, and 4.2 times as long as that of the control group, respectively. However, the migration distance of the proliferating VSMC was only one-fourth of the quiescent cells under the same effects. The results of Boyden chamber assay indicated that VSMC was capable of degrading collagen and traversed the pores of membrane barriers in response to bFGF as a chemoattractant, and VSMC number across the membrane was markedly increased as concentration gradient of bFGF ascended. Northern blot and nuclear run-off assay showed that bFGF not only stimulated the expression of migration-related matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) but also enhanced the transcription of proliferation-related osteopontin (OPN) and c-jun genes in the quiescent VSMC. bFGF could moderately increase the expression of OPN and c-jun, but had no significant effect on the expression of MMP-2 and TIMP-2 in the proliferating cells under the same conditions. These findings suggest that VSMC migration capability and the expression activity of migration- and proliferation-related genes were significantly distinct for the quiescent and proliferating VSMC. The cellular migration capability and the expression activity of migration-related genes in the quiescent VSMC were much higher than those in the proliferating cells in response to cytokines.

Animals↗

PubMed1987

Avian sarcoma virus 17 carries the jun oncogene.

Biologically active molecular clones of avian sarcoma virus 17 (ASV 17) contain a replication-defective proviral genome of 3.5 kilobases (kb). The genome retains partial gag and env sequences, which flank a cell-derived putative oncogene of 0.93 kb, termed jun. The jun gene lacks preserved coding domains of tyrosine-specific protein kinases. It also shows no significant nucleic acid homology with other known oncogenes. The probable transformation-specific protein in ASV 17-transformed cells is a 55-kDa gag-jun fusion product.

Amino Acid Sequence↗

PubMed1994

Differential expression pattern of jun B and c-jun in the rat brain during the 24-h cycle.

Data from a previous report [3] demonstrated that the proto-oncogene c-fos mRNA expression undergoes basally a circadian fluctuation in the rat brain. The present study was designed to verify by means of Northern blot hybridization the eventual occurrence of a spontaneous oscillation in the expression of other two proto-oncogenes, jun B and c-jun, during 24 h. Rats were either entrained to a light-dark photoperiod or maintained under constant darkness or light. During the dark period, as well as the subjective night, the jun B mRNA levels in the cerebral cortex and striatum were 4-6 times higher than in the light hours or subjective day. No consistent oscillation was found in the c-jun mRNA expression during 24 h in any of the examined brain regions. These results suggest the possibility of different interactions of the c-fos, jun B and c-jun gene products throughout a 24-h period in discrete brain regions.

Animals↗

PubMed2000

Activation of DNA synthesis and AP-1 by profilin, an actin-binding protein, via binding to a cell surface receptor in cultured rat mesangial cells.

Profilin is known to bind to actin monomers (to regulate actin polymerization) and to phosphatidylinositol-4,5-bisphosphate (to inhibit hydrolysis by unphosphorylated phospholipase C-gammal). It was recently reported that profilin is overexpressed in glomerular mesangial cells (MC) of rats with anti-Thy-1.1-induced glomerulonephritis and is accumulated in the extracellular space around MC. In this study, the biologic activities of extracellular profilin were examined. Scatchard analysis indicated the existence of a single class of cell surface binding sites, with similar equilibrium dissociation constants for purified splenic profilin and recombinant profilin, in cultured rat MC. Profilin increased [(3)H]thymidine incorporation in a dose-dependent manner and produced additive effects on platelet-derived growth factor-induced [(3)H]thymidine incorporation. Profilin increased AP-1 DNA-binding activity in a concentration-dependent (ED(50) = 30 nM) and time-dependent manner after transient c-jun gene expression, as measured using gel-shift assays and competitive reverse transcription-PCR. Pretreatment of profilin with an anti-profilin inhibitory antibody suppressed profilin-induced AP-1 activation and [(3)H]thymidine incorporation. Furthermore, profilin induced rapid transient activation of protein kinase C, and staurosporine and H-7 reduced the profilin-induced activation of AP-1, suggesting protein kinase C-dependent activation of AP-1. These findings indicate that profilin in the extracellular space can bind to cell surface receptors of MC and act as an inducer of signal transduction. These results suggest that extracellular profilin may be involved in the progression of glomerular diseases, by affecting cell growth.

Animals↗

PubMed1991

[Regulation of collagenase gene expression in human osteosarcoma-derived osteoblastic cell lines].

The regulation of collagenase gene expression in the human osteosarcoma-derived osteoblastic cell lines MG-63, U2-OS and human fibroblast cell line IMR-90 was investigated by Northern blot analysis. Exposure of quiescent MG-63, U2-OS and IMR-90 cells to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 10% fetal calf serum (FCS) resulted in the induction of mRNA encoding collagenase. Epidermal growth factor (EGF) induced collagenase mRNA in the IMR-90 cell but not in the MG-63 and U2-OS cells. In the IMR-90 and MG-63 cells, EGF stimulated the transcription of the c-fos and c-jun genes encoding the transcriptional factors which interact directly with the promoter region of the human collagenase gene. Parathyroid hormone and 1,25-dihydroxy-vitamin D3 did not increase the collagenase mRNA level in both osteosarcoma cells. Recombinant interleukin-1 beta (rIL-1 beta) induced collagenase and c-jun but not c-fos mRNA in the MG-63 cell. The induction by rIL-1 beta was blocked by cycloheximide and dexamethasone. Transforming growth factor beta 1 blocked the FCS-induced collagenase gene expression but partially inhibited the rIL-1 beta-induced gene expression in the MG-63 cell. These results suggest that the collagenase activity is regulated not only by post-translational modification but also at the transcriptional level by the various factors in bone.

Epidermal Growth Factor↗

PubMed1992

Two AP1 sites binding JunB are essential for human papillomavirus type 18 transcription in keratinocytes.

The activity and epithelial tropism of the human papillomavirus type 18 P105 early promoter, which directs the synthesis of the E6 and E7 transforming genes, are controlled by cis elements included in the viral long control region. To identify potential cellular regulators of this promoter, we mutagenized one or both of the 5'-TGACTAA-3' cis elements capable of interacting with the AP1 transcription factor, which is composed either of homodimers or heterodimers of the Jun products or of heterodimers of Jun and Fos. Mutation of both elements completely abolished P105 promoter activity in human keratinocytes. We show that either AP1 site can interact efficiently in vitro with any of the three different Jun products as heterodimers with c-Fos. However, in nuclear extracts prepared from human keratinocytes, JunB was the predominant Jun component bound to the DNA probe containing this cis element. These results implicate JunB as an important factor in human papillomavirus type 18 transcription in keratinocytes and strongly suggest a potential role of this Jun gene product in the tissue-specific transcription of the genital papillomaviruses.

Base Sequence↗

PubMedDate not supplied

Static magnetic field with a strong magnetic field gradient (41.7 T/m) induces c-Jun expression in HL-60 cells.

We investigated the effects of 6- and 10-T static magnetic fields (SMFs) on the expression of protooncogenes using Western blot immunohybridization methods. We used a SMF exposure system, which can expose cells to a spatially inhomogeneous 6 T with a strong magnetic field (MF) gradient (41.7 T/m) and a spatially homogeneous 10 T of the highest magnetic flux density in this experiment. HL-60 cells exposed to either 6- or 10-T SMF for periods of 1 to 48 h did not exhibit remarkable differences in levels of c-Myc and c-Fos protein expression, as compared with sham-exposed cells. In contrast, c-Jun protein expression increased in HL-60 cells after exposure to 6-T SMF for 24, 36, 48, and 72 h. These results suggest that a homogeneous 10-T SMF does not alter the expression of the c-jun, c-fos, and c-myc protooncogenes. However, our observation that exposure to a strong MF gradient induced c-Jun expression suggests that a strong MF gradient may have significant biological effects, particularly regarding processes related to an elevation of c-jun gene expression.

Electromagnetic Fields↗

PubMed1993

Differential regulation of early response genes and cell proliferation through the human granulocyte macrophage colony-stimulating factor receptor: selective activation of the c-fos promoter by genistein.

Granulocyte macrophage colony-stimulating factor (GM-CSF) binds to the high-affinity GM-CSF receptor (GMR) consisting of alpha and beta subunits and induces rapid tyrosine phosphorylation, activation of early response genes, and proliferation of hematopoietic cells. The alpha subunit is the primary cytokine binding component and the beta subunit is required for high-affinity binding as well as for signal transduction. Using tyrosine kinase inhibitors and cytoplasmic deletion mutants of the beta subunit, we obtained evidence that there are at least two distinct pathways downstream of the GMR in BA/F3 cell, one which is essential for proliferation, leads to the c-myc gene activation, and is sensitive to herbimycin and genistein. Activation of this pathway depends on the cytoplasmic region between amino acid positions 455 and 517 of the beta subunit. The second pathway, which leads to activation of c-fos and c-jun genes, is only partially sensitive to herbimycin, is resistant to genistein and depends on the region between amino acid positions 626 and 763 of the beta subunit. Unexpectedly, the c-fos mRNA induction was augmented by genistein. The enhanced expression of c-fos mRNA by genistein also occurred with stimulation with cAMP, PMA, or EGF in NIH3T3 cells. It thus seems likely that genistein affects a common pathway downstream of these signals.

Animals↗

PubMed2005

Cocaine up-regulates Fra-2 and sigma-1 receptor gene and protein expression in brain regions involved in addiction and reward.

Sigma receptors have recently been implicated in the actions of cocaine, and antagonists of these receptors prevent many acute and subchronic cocaine effects. A previous study revealed that the immediate early gene fra-2 is up-regulated after cocaine administration, and this effect is prevented by the sigma-1 receptor antagonist BD1063 [1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine]. In the present study, the effects of cocaine and BD1063 on the expression of six fos and jun genes were evaluated in mouse brains using cDNA microarrays. Several of these genes were altered by cocaine, but only the alteration in fra-2 was prevented by BD1063. The time courses of fra-2 and sigma-1 receptor gene and protein expression in different brain regions were also determined. Cocaine up-regulated fra-2, which was followed by a later up-regulation of sigma-1 receptors. The cocaine-induced up-regulation of fra-2 and sigma-1 receptor genes and proteins were detected in whole brain, striatum, and cortex, but not in cerebellum. All of these cocaine-induced effects were prevented by BD1063. The interaction between cocaine, fra-2, and sigma-1 receptors involves brain regions that are established components of the neural circuit for reward, suggesting that they may contribute to the enduring changes that underlie the cellular basis of drug abuse.

Actins↗

PubMed2002

Redox regulation of adenovirus-induced AP-1 activation by overexpression of manganese-containing superoxide dismutase.

Adenovirus gene therapy is a promising tool in the clinical treatment of many genetic and acquired diseases. However, it has also caused pathogenic effects in organs such as the liver. The redox-sensitive transcription factors AP-1 and NF-kappaB have been implicated in these effects. To study the mechanisms of adenovirus-mediated AP-1 and NF-kappaB activation and the possible involvement of oxidative stress in adenovirus transduction, rats were injected with either replication-defective recombinant adenovirus with DNA containing the cytomegalovirus promoter region only (AdCMV), adenovirus containing human manganese-containing superoxide dismutase (MnSOD) cDNA (AdMnSOD), or vehicle. Compared to vehicle and AdCMV transduction, MnSOD gene transfer yielded a fivefold increase in liver MnSOD activity 7 days postinjection. Gel shift assay showed that AdCMV transduction induced DNA binding activity for AP-1 but not NF-kappaB. MnSOD overexpression abolished this activation. Western blotting analysis of c-Fos and c-Jun suggested that up-regulation of c-fos and c-jun gene expression does not directly contribute to the induction of AP-1 activation. Glutathione/glutathione disulfide ratios were decreased by adenovirus transduction and restored by MnSOD overexpression. The AP-1 binding activity that was induced by AdCMV was decreased by immunoprecipitation of Ref-1 protein. Ref-1 involvement was confirmed by restoration of AP-1 binding activity after the immunoprecipitated Ref-1 protein had been added back. AP-1 DNA binding activity was also elevated in control and AdMnSOD-injected rats after addition of the immunoprecipitated Ref-1 protein. These data indicate that cellular transduction by recombinant adenovirus stimulates AP-1 DNA binding activity. Furthermore, our results suggest that MnSOD overexpression decreases AP-1 DNA binding activity by regulating intracellular redox status, with the possible involvement of Ref-1 in this redox-sensitive pathway.

Adenoviridae↗

PubMed1993

AP-1 activity during normal human keratinocyte differentiation: evidence for a cytosolic modulator of AP-1/DNA binding.

Increased levels of c-fos and c-jun expression have been observed in differentiating epithelial cells. However, no data are available on activator protein 1 (AP-1) activity during keratinocyte differentiation. In this work we investigated c-fos and c-jun gene expression and AP-1-(12-O-tetradecanoylphorbol-13-acetate)-responsive enhancer element (TRE) binding activity during keratinocyte differentiation utilizing both authentic and in culture-reconstituted human epidermis. We demonstrate that: (i) in reconstituted epidermis, non-differentiated and differentiated keratinocytes express equivalent levels of c-Jun, while in reconstituted epidermis permanently grafted onto athymic mice, as well as in authentic epidermis, c-Jun is predominantly expressed in the granular layer of the tissue. Equivalent levels of c-fos expression have been found in all the layers of both reconstituted and authentic epidermis. (ii) Nuclear extracts from cultures enriched in differentiated keratinocytes display an 80-90% reduction of AP-1 activity when compared to extracts from cultures enriched in nondifferentiated cells. (iii) Cytosolic extracts obtained from cultures enriched in differentiated cells reduce, in a concentration-dependent manner, the AP-1 activity present in nuclear extracts of both mammalian and Drosophila cells. (iv) The specific TRE binding activity of a recombinant c-Jun protein is significantly reduced by cytosolic extracts of differentiated keratinocytes, while the specific DNA binding of the purified recombinant human homeoprotein HOX4B is not. (v) The dephosphorylation, by alkaline phosphatase, of cytosolic extracts increases the inhibitory activity already present or makes evident a latent activity.

Animals↗

PubMed1991

Regulation of jun and fos gene expression in human monocytes by the macrophage colony-stimulating factor.

The macrophage colony-stimulating factor (M-CSF) is required for the growth and differentiation of mononuclear phagocytes. However, the signaling events responsible for these effects remain unclear. The present studies have examined the effects of M-CSF on potential signaling pathways involving expression of the jun and fos early response genes. Low levels of c-jun transcripts were detectable in resting human peripheral blood monocytes. Treatment of these cells with 10(3) units/ml human recombinant M-CSF was associated with rapid and transient increases in c-jun mRNA levels. Nuclear run-on assays and mRNA stability studies demonstrated that M-CSF regulates c-jun expression by both an increase in transcription rate and a prolongation in the half-life of c-jun transcripts. M-CSF treatment was also associated with a rapid induction of the jun-B gene, although expression of this gene was prolonged compared to that of c-jun. We further demonstrate that M-CSF increases c-fos mRNA levels in human monocytes through control at both the transcriptional and posttranscriptional levels. Maximal induction of the c-fos gene was followed by that for the fos-B gene. Moreover, M-CSF-induced expression of the fos-related gene, fra-1, was delayed compared to that for both c-fos and fos-B. Taken together, the results indicate that M-CSF treatment is associated with differential activation of multiple members of the jun/fos family and that expression of these genes could contribute to nuclear signaling mechanisms that regulate a specific program of monocyte differentiation.

Cell Nucleus↗

PubMed2005

No involvement of the nerve growth factor gene locus in hypertension in spontaneously hypertensive rats.

Sympathetic hyper-innervation and increased levels of nerve growth factor (NGF), an essential neurotrophic factor for sympathetic neurons, have been observed in the vascular tissues of spontaneously hypertensive rats (SHRs). Such observations have suggested that the pathogenesis of hypertension might involve a qualitative or quantitative abnormality in the NGF protein, resulting from a significant mutation in the gene's promoter or coding region. In the present study, we analyzed the nucleotide sequences of the cis-element of the NGF gene in SHRs, stroke-prone SHRs (SHRSPs), and normotensive Wistar-Kyoto (WKY) rats. The present analyses revealed some differences in the 3-kb promoter region, coding exon, and 3' untranslated region (3'UTR) for the NGF gene among those strains. However, the observed differences did not lead to changes in promoter activity or to amino acid substitution; nor did they represent a link between the 3'UTR mutation of SHRSPs and elevated blood pressure in an F2 generation produced by crossbreeding SHRSPs with WKY rats. These results suggest that the NGF gene locus is not involved in hypertension in SHR/ SHRSP strains. The present study also revealed two differences between SHRs and WKY rats, as found in cultured vascular smooth muscle cells and in mRNA prepared from each strain. First, SHRs had higher expression levels of c-fos and c-jun genes, which encode the component of the AP-1 transcription factor that activates NGF gene transcription. Second, NGF mRNAs prepared from SHRs had a longer 3'UTR than those prepared from WKY rats. Although it remains to be determined whether these events play a role in the hypertension of SHR/SHRSP strains, the present results emphasize the importance of actively searching for aberrant trans-acting factor(s) leading to the enhanced expression of the NGF gene and NGF protein in SHR/SHRSP strains.

Animals↗

PubMed1999

Modulation of excision repair cross complementation group 1 (ERCC-1) mRNA expression by pharmacological agents in human ovarian carcinoma cells.

Excision repair cross complementation group 1 (ERCC-1) is a DNA repair gene that is essential for life, and it appears to be a marker gene for nucleotide excision repair activity. Overexpression of ERCC-1 during cisplatin-based chemotherapy is associated with clinical and cellular drug resistance. We therefore began to assess the influence of various pharmacological agents on the induction of ERCC-1 mRNA in A2780/CP70 human ovarian carcinoma cells. Cisplatin exposure in culture resulted in a 4- to 6-fold induction for the steady-state level of ERCC-1 mRNA in A2780/CP70 cells. ERCC-1 mRNA induction was concentration and time dependent. Cyclosporin A and herbimycin A, which suppress c-fos and c-jun gene expressions, respectively, blocked the cisplatin-induced increase in ERCC-1 mRNA. This effect of cyclosporin A or herbimycin A on the down-regulation of ERCC-1 correlates with enhanced cytotoxicity of cisplatin in this system. The products of c-fos and c-jun are components of the transcription factor AP-1 (activator protein 1). 12-O-Tetradecanoylphorbol 13-acetate (TPA), a known AP-1 agonist, induced ERCC-1 mRNA to the same extent as cisplatin, but did not synergize with cisplatin in this regard. The TPA effect was biphasic, with an initial increase during the first 1-6 hr, followed by decreasing mRNA levels at 24-72 hr. These data suggest that the effects of these pharmacological agents on ERCC-1 gene expression may be mediated through the modulation of AP-1 activities.

Benzoquinones↗

PubMed1996

Expression of c-fos and c-jun proteins and AP-1 binding activity during cell cycle progression of HL60 cells and phytohemagglutinin-stimulated lymphocytes.

The protein products of the c-fos (p62c-fos) and c-jun (p39c-jun) genes are members of the AP-1 transcription factor family and are thought to play important roles in the regulation of gene expression during the cell cycle. Most studies on the expression of these proteins in relation to the cell cycle have been performed at the mRNA level, and therefore do not give direct information about the presence of the proteins during the cell cycle. We have used Western blotting to investigate the presence of these proteins during the cell cycles of two different cellular systems: a continuously growing myeloid leukemic cell line, HL60, and normal cells stimulated into cycle, phyto- hemagglutinin (PHA)-stimulated normal human peripheral blood lymphocytes (PBL). The binding activity of transcription factor AP-1, which consists of dimers of Fos and Jun family proteins, was also studied using a gel shift assay. We found nuclear p62c-fos, p39c-jun, and AP-1 binding activity throughout the cell cycle both in HL60 cells and in PHA-stimulated PBL, and we postulate that these proteins are required throughout the cell cycle and not transiently in the G0 to G1 transition as previous mRNA studies have indicated. We demonstrated an uncoupling of AP-1 binding activity from p62c-fos, and p39c-jun AP-1 activity was expressed more strongly in the G1- and G2/M-phase enriched samples than in the S-phase enriched samples of HL60 cells, while levels of nuclear p62c-fos and p39c-jun were constant. Nuclei of unstimulated PBL from different donors expressed p62c-fos and p39c-jun, but AP-1 was not detected in the majority of samples. Following PHA stimulation of PBL, the increase in AP-1 activity was delayed with respect to the augmentation of p39c-jun expression. We also observed that cytoplasmic p62c-fos and p39c-jun were present in HL60 cells and PHA-stimulated PBL. However, no cytoplasmic p62c-fos was detected in unstimulated PBL, although in some cases cytoplasmic p39c-jun was detected, suggesting that subcellular compartmentalization of these proteins may occur under certain circumstances.

Base Sequence↗