Oncogene database

3726

JUNB

jun B proto-oncogene;JUNB;jun B proto-oncogene

activator protein 1|transcription factor jun-B

19p13.2

protein-coding

We have shown previously that angiotensin-II (A-II) controls proto-oncogene (c-fos, jun-B and c-jun) mRNA accumulation in bovine adrenal fasciculata cells (BAC). Since BAC contain both subtypes (AT-1 and AT-2) of the A-II receptor, we have investigated which subtype was involved in the effect of A-II on proto-oncogene mRNA by using a selective antagonist for AT-1 (DUP 753) and for AT-2 (CGP 42112A). DUP 753, but not CGP 42112A, inhibited the stimulatory effect of A-II on proto-oncogene mRNA, with ID50s of 4 x 10(-7) M, 7 x 10(-7) M and 2 x 10(-6) M for c-fos, jun-B and c-jun, respectively. Neither of the two antagonists by themselves had a direct effect on proto-oncogene mRNA. As the A-II AT-1 receptors are coupled to the phospholipase C system in BAC, we have investigated whether the A-II effects on the proto-oncogenes were mediated by protein kinase C (PKC) or by Ca2+ calmodulin. First, activation of PKC by the phorbol ester, PMA, increased the level of three proto-oncogene mRNAs, whereas calcium ionophore had no effect. Second, staurosporine, a specific inhibitor of PKC, reduced the stimulatory action of A-II on proto-oncogene mRNA by 80-90%, whereas trifluoroperazine, an inhibitor of calmodulin, had no significant effect. These results demonstrate that the effects of A-II on proto-oncogene mRNA are mediated by AT1 receptor subtypes, mainly through activation of the PKC pathway.

During embryogenesis, growth and differentiation occur in a sequential, predetermined order suggesting that specific genes are turned on and off in a precise and well-regulated manner. Placental development, which is characterized by massive proliferation and differentiation of multiple cell types, must be similarly regulated. Early response protooncogenes, such as c-jun and jun-B, have been associated with both proliferation and differentiation of different cell types. In this study, using Northern blot analysis, we found that c-jun and jun-B expression occurred in human placentas throughout gestation. Maximal expression of c-jun occurred in early gestation, and maximal expression of jun-B occurred in late gestation. We speculate that peak expression of c-jun in human placenta at early gestation may be related to cytotrophoblastic proliferation and that peak expression of jun-B in late gestation may be related to further terminal differentiation of trophoblastic cells.

Anaplastic large cell lymphomas (ALCLs) are highly proliferating tumors that commonly express the AP-1 transcription factor JunB. ALK fusions occur in approximately 50% of ALCLs, and among these, 80% have the t(2;5) translocation with NPM-ALK expression. We report greater activity of JunB in NPM-ALK-positive than in NPM-ALK-negative ALCLs. Specific knockdown of JUNB mRNA using small interfering RNA and small hairpin RNA in NPM-ALK-expressing cells decreases cellular proliferation as evidenced by a reduced cell count in the G2/M phase of the cell cycle. expression of NPM-ALK results in ERK1/2 activation and transcriptional up-regulation of JUNB. Both NPM-ALK-positive and -negative ALCL tumors demonstrate active ERK1/2 signaling. In contrast to NPM-ALK-negative ALCL, the mTOR pathway is active in NPM-ALK-positive lymphomas. Pharmacological inhibition of mTOR in NPM-ALK-positive cells down-regulates JunB protein levels by shifting JUNB mRNA translation from large polysomes to monosomes and ribonucleic particles (RNPs), and decreases cellular proliferation. Thus, JunB is a critical target of mTOR and is translationally regulated in NPM-ALK-positive lymphomas. This is the first study demonstrating translational control of AP-1 transcription factors in human neoplasia. In conjunction with NPM-ALK, JunB enhances cell cycle progression and may therefore represent a therapeutic target.

Although the structure of several members of the GH receptor family has been defined, signal transduction following GH binding to its receptor has not been elucidated. Mouse osteoblasts were used to study the effect of GH on immediate early gene expression and, subsequently, the cellular signal(s) mediating this expression were analysed. GH rapidly and transiently induced the expression of c-jun and jun B in concert with the already reported expression of c-fos. The GH-induced expression of c-fos was completely blocked by the protein kinase inhibitors staurosporine and H7, indicating that the action of GH is mediated by one or several protein kinases. We next analysed the identity of the putative protein kinases in more detail by using a more specific protein kinase inhibitor, namely the ether-lipid 1-O-alkyl-2-O-methylglycerol, understood to be an inhibitor of protein kinase C (PKC). Data obtained from these studies revealed that GH-induced expression of c-fos is mediated by PKC. In addition, we observed a profound increase in formation of the PKC activator diacyglycerol upon addition of GH, a natural activator of PKC. In conclusion, upon binding of GH to mouse osteoblasts, the receptor-mediated cellular signal involves diacyglycerol formation and activation of PKC, leading to the induction of oncogene expression. Finally, the expression of c-fos, c-jun and jun B results in an increased binding of protein complexes to AP-1 binding sites.

Type beta transforming growth factor (TGF-beta) is a multifunctional regulator of cell growth and differentiation. In the BC3H1 muscle cell line, TGF-beta blocks the onset of differentiation when added to undifferentiated myoblasts and causes dedifferentiation when added to fully differentiated myocytes. The goal of the present study was to determine whether TGF-beta-dependent repression of muscle-specific genes was preceded by modulation in expression of members of the jun proto-oncogene family, which function as growth factor-inducible transcription factors. junB mRNA was expressed at a basal level in differentiated BC3H1 myocytes. Within 15 min following exposure of myocytes to TGF-beta, junB mRNA began to accumulate; a peak of expression 20-fold above basal levels was observed after 2 h with a gradual decline thereafter. Nuclear run-on transcription assays showed that induction of junB by TGF-beta occurred at the level of transcription through a mechanism independent of protein synthesis. junB was also induced by 20% fetal bovine serum, platelet-derived growth factor, and insulin, but the maximal level of expression in response to these growth factors was lower and less sustained than in the presence of TGF-beta. In contrast to the dramatic effects of TGF-beta on junB expression, c-jun showed only a 2.5-fold increase in expression in response to TGF-beta. In an effort to identify additional members of the jun family which might be regulated by TGF-beta, a cDNA library was prepared from the poly(A)+ mRNA of TGF-beta-stimulated BC3H1 myocytes and was screened under conditions of reduced stringency with a v-jun DNA probe. From this screen, a new jun-related gene product was identified which shared a high degree of homology with regions of c-jun and junB which have been implicated in transcriptional activation, dimerization, and DNA binding. The transcript for this jun-related gene was expressed constitutively in BC3H1 cells and was not regulated by TGF-beta. Three members of the jun family thus exhibit distinct responses to TGF-beta in BC3H1 cells. The rapid transcriptional induction of junB is among the earliest and most dramatic responses to TGF-beta yet described and suggests that junB may mediate certain of the diverse biological effects of this growth factor.

The three members of the jun proto-oncogene family c-jun, jun b and jun D were mapped on the mouse chromosome by in situ hybridization. The c-jun locus is on chromosome 4 subregion C5----C7, whereas jun B and jun D are co-localized on chromosome 8 subregion C. RFLP analysis of interspecific hybrids confirmed the mapping of jun B and D and showed that they are situated about 7.3 +/- 3.5 cM apart. Thus despite their possible origin from a single ancestral gene they are not closely linked on the chromosome. Using the same probes, we showed that the human genome also contains sequences homologous to the mouse jun B and jun D. They are located on human chromosome 19 p13.2, a region that may be involved in chromosomal translocation in acute lymphocytic leukemia (ALL), acute nonlymphocytic leukemia (ANLL) and malignant melanoma (MEL). Finally, the present data identify a new segmental homology between mouse and human chromosomes.

Anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35) resulting in expression of NPM1(NPM)-ALK oncogenic kinase. The latter is capable of activating ERK kinase, which upregulates JUNB expression through ETS1. JUNB, in turn, interacts with the TNFRSF8 (CD30) gene promoter and induces CD30 (TNFRSF8) overexpression. However, the role of CD30 overexpression in ALK+ ALCL oncogenesis remains unknown. Here we show that the JUNB gene is frequently amplified in ALK+ ALCL, suggesting gene amplification as an additional underlying mechanism for JUNB overexpression. Silencing of JUNB resulted in reduced cell growth and colony formation associated with decreased activator protein-1 activity and G1/S and G2/M cell cycle arrest. These effects were linked to decreased CD30 levels, downregulation of CCNA2 (Cyclin A), CCND2 (Cyclin D2) and CCND3 (Cyclin D3) and upregulation of cyclin-dependent kinase inhibitors CDKN2A (p14) and CDKN1A (p21), but not CDKN1B (p27). Similar cell cycle changes were observed following the knock-down of TNFRSF8 gene or blockade of its function using anti-CD30 antibodies, which were associated with upregulation of CDKN2A and CDKN1A, but not CDKN1B. These findings indicate that JUNB may partly operate through CD30 signalling. Silencing of JUNB also sensitized NPM1-ALCL+ cells to standard chemotherapeutic agents. Our findings uncover the oncogenic role of the JUNB/CD30 axis and its potential as therapeutic target in ALK+ ALCL.

The E5a gene of human papillomavirus type 11 (HPV-11) is a transforming oncogene. In this study, we investigated the mechanism of E5a induced transformation. Our results show that the expression of c-jun and junB, but not junD, was activated by HPV-11 E5a in NIH 3T3 cells and human epidermal keratinocytes. However, the expression of c-fos was activated by E5a in NIH 3T3 cells, but not in keratinocytes. We further investigated the mechanism of c-jun and junB induction by E5a. The amount of c-jun and junB RNAs correlated with the amount of E5a RNA in the heavy metal inducible system. E5a constitutively activated the expression of c-jun and junB at the initiation of transcription level. In addition, analyses of the effect of serum on c-jun expression in E5a transformed human epidermal keratinocytes show that EGF might have a stimulatory effect on c-jun gene expression in E5a expressing keratinocytes.

We describe here structural and expression analysis of the jun-B oncogene in two cervical cancer cell lines. In the CC7T-a cell line, results from both Southern analysis and cDNA cloning studies revealed the existence of two structurally altered jun-B alleles besides the normal gene. One of the altered alleles was due to a type 16 human papillomavirus (HPV-16) integration event, whereas the other allele was a consequence of a chromosomal translocation involving chromosome 19 (jun-B) and an EST182 locus residing in chromosome 15. In the HeLa cell line, which contains integrated HPV-18, an apparent structural aberration, a 3-fold amplification and a 3-fold overexpression of the jun-B gene were observed. Our observations suggest that deregulation of the jun-B gene expression may have contributed to the transformation process in these two cervical cancer cell lines.

We previously described the isolation of non-tumorigenic revertants from mutagenized populations of v-fos-transformed Rat-1 cells (Zarbl et al., 1987). In the present study we examined the possibility that the revertant phenotype resulted from mutations that altered the expression or activities of the c-jun or junB proto-oncogenes. The results demonstrated that levels of the c-jun mRNA and protein were unchanged in the revertants when compared to the transformed parental cells, and ectopic overexpression of c-jun failed to retransform the revertants. Although one mutant allele was detected in revertant EMS-1-19, overexpression of this mutant allele failed to inhibit v-fos induced cell transformation. Together these results indicated that the revertant phenotype did not result from altered expression or mutations in the c-jun gene. In contrast to the results obtained with c-jun, the levels of junB mRNA and protein were found to be reduced two- or threefold in revertant EMS-1-19. Ectopic overexpression of junB induced transformation of revertant EMS-1-19, but failed to transform Rat-1 cells. Moreover, about 10% of v-fos transformed cells transfected with vectors that express antisense junB mRNA acquired a non-transformed phenotype. Together these results indicate that expression of junB above a threshold level is essential for v-fos-induced transformation of Rat-1 fibroblasts.

In this study, we show that HPV-16 E5 induced anchorage-independent growth in immortalized human epidermal keratinocytes and that HPV-16 E5 in human keratinocytes had higher expression of c-jun and junB; also, we investigated the role of transcriptional initiation pathways in the expression elevation. In addition, Ras-dependent pathway, as well as PKC-dependent pathway, leads to HPV-16 E5-induced c-jun gene expression.

The transcription factor junB belongs to the jun family of protooncogenes. The appearance of junB mRNA in hepatic cells is an extremely early and sensitive marker of the action of proinflammatory cytokines including interleukin-6. In this study, a competitive reverse transcription (RT)-PCR assay has been developed that is suitable for the quantitative determination of junB mRNA expression. This nonisotopic assay compared to other methods (e.g., Northern blot) is a fast and convenient way to determine the expression of the junB gene and thus the immediate concentration- and time-dependent action of interleukin-6. Because interleukin-6 and interleukin-6-type cytokines play a highly important regulatory role in various pathophysiologically important processes, such as hepatic acute-phase reaction, the quantitative assay of junB mRNA completes the scale of laboratory approaches in inflammation and among other pathological conditions.

Human placental cytotrophoblast cells differentiate by a process of fusion into a syncytium. This process is stimulated by EGF but also occurs spontaneously at a slower rate in cultured cytotrophoblast cells. To determine nuclear proto-oncogene changes mediating these events, c-myc, c-fos, c-jun and junB were measured in spontaneously differentiating cells and in cells exposed to EGF. c-myc showed a transient rise in expression at 4-8 h with augmented expression by EGF, occurring even in the absence of serum or attachment. c-myc and c-jun declined during culture, but c-fos and particularly junB showed increased expression by day 3 with marked responses to EGF stimulation. Syncytia induced to form by EGF exposure for 48 h demonstrated marked junB expression after rechallenge with 40 min EGF exposure, but negligible responses of c-fos and c-jun. c-myc showed increased expression after 6 h EGF exposure throughout the culture period and in syncytia. The results indicate EGF promotes a syncytial phenotype characterized by c-fos and junB expression during syncytial formation. EGF continues to elicit junB and c-myc responsiveness in more mature syncytium, indicative of continued EGF actions which may include acting as a survival factor, as an hCG secretagogue, and as an inducer of continued development of the syncytium.