Jun Proto-oncogene Family Research Articles

Promotion of Morphological Transformation by di- n-butyltin Dichloride in C3H/10T1/2 Cells: Prediction by Prior Expression of Tumour Promoter-Responsive Genes

Previous studies in our laboratory have shown that chemical treatments may induce increases in proliferin gene family mRNA accumulation in cultured murine embryonic cells. Proliferin inductions are highly correlated with subsequent promotional outcomes during two-stage focus-formation assays in C3H/10T1/2 cell cultures. In work reported here, the strong affiliation between these two responses was further validated after treating cells with di -n-butyltin dichloride which is a polyvinyl chloride (PVC) plastic additive that often contaminates food and water. Increased proliferin expression and promotion of morphological transformation occurred at similar concentrations. Promotion of transformation was detected at di- n-butyltin dichloride concentrations of 80 n m (24 ng/ml) and above, if added to initiated cultures before confluent monolayers had formed. Proliferin induction and morphological transformation were both reduced in confluent cultures treated with di -n-butyltin dichloride, as compared to subconfluent cultures. Proliferin expression measured in near-confluent cultures was induced up to 10-fold during the 36-hr period following di -n-butyltin dichloride exposure and was accompanied by increased accumulation of transcripts from many genes regulated by oxidative stresses, growth-inducing agents, and/or other promoting agents (asbestos, superoxide radicals ). Di -n-butyltin dichloride-induced mRNA species included members of the fos and jun proto-oncogene families, c-myc, egr1, ribonucleotide reductase (R2 subunit), odc, macrophage chemotactic protein/je, hsp70, metallothionine IIA, c-sod and mn-sod. The observed patterns of RNA accumulation suggested that a small subset of mRNA species, including proliferin, exhibit regulatory behaviour as a response to dissimilar agents or conditions that promote focus-formation in C3H/10T1/2 cultures. Plausible predictions of promotional effects in two-stage morphological transformation assays can be made from gene-expression responses to test agents.

Oxidants, transcription factors, and intestinal inflammation.

It is now well appreciated that chronic gut inflammation is characterized by enhanced production of reactive metabolites of oxygen and nitrogen. Some of these oxidants are known to modulate the expression of a variety of genes that are involved in the immune and inflammatory responses. For example, certain oxidants are known to activate the nuclear transcription factor kappa B, which regulates the expression of a variety of different adhesion molecules, cytokines, and enzymes. Oxidants are also known to activate another transcription factor, activator protein-1. This transcription factor is composed of products from the fos and jun proto-oncogene family and is believed to be important in regulating cell growth and proliferation. Finally, oxidants are believed to promote intestinal epithelial cell apoptosis, and the B-cell lymphoma/leukemia-2 gene product is believed to inhibit this phenomenon in an antioxidant-dependent manner. Taken together, these observations suggest that nontoxic concentrations of reactive metabolites of oxygen and nitrogen play an important role in regulating the expression of genes involved in the inflammatory response and in modulating apoptosis.

Follicle-stimulating hormone increases the expression of tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2 and induces TIMP-1 AP-1 site binding complex(es) in prepubertal rat Sertoli cells.

Primary cultures of prepubertal rat Sertoli cells secrete two major tissue inhibitors of metalloproteinases: TIMP-1 (M(r) 28K) and TIMP-2 (M(r) 21 K). FSH stimulated Sertoli cell TIMP-1 and TIMP-2 activity in a time- and dose-dependent manner and also stimulated TIMP-1 and TIMP-2 protein and messenger RNA levels. These effects were mimicked by the cAMP analog, 8-bromo-cAMP, and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. The protein kinase C activating phorbol ester phorbol myristate acetate (TPA) stimulated TIMP-1 but not TIMP-2 activity and messenger RNA levels. Cycloheximide and actinomycin-D inhibited basal TIMP-1 and TIMP-2 activity and inhibited the ability of FSH, 8-bromo-cAMP, and TPA to stimulate TIMP activity. The protein kinase A (PKA) inhibitor AMP Rp isomer did not affect basal TIMP-1 and TIMP-2 activity or TPA-stimulated TIMP-1 activity. However, the PKA inhibitor markedly reduced FSH and 3-isobutyl-1-methylxanthine stimulation of TIMP-1 and TIMP-2 activity. FSH, 8-bromo-cAMP, and TPA stimuli induced DNA binding complexes capable of binding to a TIMP-1 AP-1 site consensus sequence oligonucleotide. The AP-1 site binding complex(es) induced by all three treatments reacted with antibodies directed broadly against fos and jun protooncogene families and against the specific family members c-fos, junB, and junD but not c-jun proteins. Constitutive cAMP response element binding activity capable of binding an artificial cAMP response element binding site oligonucleotide was demonstrated in Sertoli cell nuclear extracts. This activity was minimally modulated by FSH, 8-bromo-cAMP, or TPA treatment. In summary, Sertoli cells secrete TIMP-1 and TIMP-2 that can be coordinately up-regulated by FSH through a cAMP, PKA-dependent pathway. a convergence of TPA, FSH, and cAMP mediated signals in prepubertal Sertoli cells may occur with the induction of specific AP-1 site binding complex(es) containing jun and fos proteins. Our data suggest that FSH stimulation of TIMP-2 expression may be regulated independently to that of TIMP-1. We propose that the ability of FSH to stimulate Sertoli cell TIMP activity suggests a central role for this hormone in the control of extracellular matrix turnover during testicular development at the level of metalloproteinase inhibition.

The effects of the insulin-like growth factors and transforming growth factor ? on the jun proto-oncogene family in MC3T3-E1 cells

Previous studies have demonstrated that when cells of the mouse osteoblastic cell line MC3T3-E1 are exposed to IGF-I and IGF-II they exhibit rapid and transient induction of the transcript from the proto-oncogene c-fos [8]. To clarify the relationship between induction of cell proliferation and proto-oncogene expression in MC3T3-E1 cells, the acute affects of IGF-I and IGF-II, growth factors that stimulate cell proliferation, and of TGF-beta 1, which inhibits cell proliferation, northern analyses with cDNA-derived probes for the proto-oncogenes c-jun, jun-B, and jun-D were undertaken. Concurrent northern analyses with a probe for c-fos extended our previous results to include the effect of TGF-beta 1 on c-fos. IGF-I does not induce the c-jun, jun-B, or jun-D transcripts, the former and latter being produced at detectable levels constitutively. After 1 hour of exposure to IGF-II the c-jun transcript response ranges from onefold to 13-fold and the jun-D transcript response ranges around two-fold. After 1 hour of exposure to TGF-beta 1, the jun-B transcript response ranges from eightfold to 24-fold, the c-fos transcript response ranges between sixfold and sevenfold. The differences observed in the magnitude and kinetics of the induction provoked by these growth factors is consistent with the presence of a regulatory circuit acting through the Jun family members which may act to stimulate transcription differentially when bound to DNA either as homodimers or, with Fos family proteins, as heterodimers.

Estrogen differentially affects c-jun expression in uterine tissue compartments.

Estrogen rapidly induces expression of the jun immediate early gene family in mature and immature rodent uteri, suggesting that these protooncogenes are directly involved in the proliferative response of the uterus to estrogen. The jun family mRNAs, however, have not been localized to specific uterine cell types. Furthermore, it is necessary to differentiate between the response of the immature vs. the mature rat uterus to 17 beta-estradiol (E2-17 beta), because in the former, all uterine cell types respond to estrogen with increased DNA synthesis, but in the latter, the proliferative response is restricted to the uterine epithelial cells. In the present study, in situ hybridization was used to determine the cell type-specific location of mRNA encoding the immediate early genes c-jun, jun-B, and jun-D after the administration of E2-17 beta to mature and immature rats. Estradiol stimulated jun-B and jun-D expression primarily in the uterine luminal and glandular epithelium. The pattern of c-jun expression, however, was strikingly different; E2-17 beta repressed c-jun mRNA levels in the uterine luminal epithelium and simultaneously increased c-jun expression in the uterine myometrium. In mature vs. immature uteri, the general cell type-specific patterns of jun-B and jun-D expression were similar after estrogen administration. The expression of c-jun was increased by estrogen in the uterine glands as well the uterine myometrium of immature rats; however, in mature rats, uterine glandular epithelial cells did not respond to E2-17 beta administration with increased c-jun expression. These experiments demonstrate for the first time positive and negative regulatory actions of estrogen on c-jun expression and suggest a role for tissue-specific factors in the control of c-jun expression. The lack of maturational effects on jun gene expression implies that the differential response of the immature vs. the mature uterus to estrogen, in terms of cell proliferation, involves a point of control other than that at the level of the jun protooncogene family.

Thyrotropin-Releasing Hormone Stimulates in Parallel jun B and c- fos Messenger Ribonucleic Acids in GH3B6 Pituitary Cells: Comparison with PRL Secretion

The hypothalamic neuropeptide TRH stimulates PRL release and PRL gene transcription in GH3B6 rat pituitary cells. In this model, TRH also raises c-fos proto-oncogene mRNA levels. c-fos is assumed to be involved in the transduction of external signals to the nucleus as a component of AP1 transcription factor, a complex that contains a member of the jun proto-oncogene family. Hence, the main aim of this study was to look for the expression of c-jun, jun B, and jun D proto-encogenes in TRH-stimulated GH3B6 cells, compared to c-fos mRNA levels and PRL secretion. This was performed using serum-starved cells. Northern blotting and dot blotting revealed that jun B mRNA were expressed at noticeable levels in control cells and were strongly stimulated by TRH. This stimulation was dose-dependent and exhibited an early peak and a long-lasting plateau phase stabilized at 4 h, similar to TRH-induced c-fos mRNA induction. c-jun mRNA was expressed at minute levels in control cells and was transiently stimulated by TRH. The jun D message was not detected. TRH-induced jun B and c-fos responses were characteristic of immediate early genes as shown by the superinduction observed under cycloheximide treatment and the total inhibition elicited by actinomycin D. Finally, the responses to serum at 30 min and 4 h revealed differences among the proto-oncogenes studied and indicate that the action of TRH is specific. Altogether, the common biphasic pattern of jun B and c-fos mRNA regulation by the neuropeptide suggests that the heterodimer Jun B/c-Fos could participate in TRH-induced PRL secretion and PRL gene transcription in GH3B6 cells.

β‐Adrenergic treatment of C6 glioma cells produces opposite changes in c‐fos and c‐jun mRNA levels

The AP1 transcriptional complex is a heterodimer composed of proteins encoded by the fos and jun proto-oncogene families. Changes in the concentration and composition of AP1 occur after cells are perturbed in a variety of different ways (Curran, in Reddy et al., eds. "The Oncogene Handbook," Amsterdam: Elsevier, pp 307-325, 1988; Sonnenberg et al., Neuron 3:359-365, 1989). Transient changes in AP1 content presumably result in altered expression of AP1-regulated target genes, that help to mediate the cell's long-term response to changes in its environment. One factor that may be important in determining which target genes are regulated by AP1 in a given context is the identity of the jun family member present in the complex (Chiu et al., Cell 59:979-986, 1989; Schutte et al., Cell 59:987-997, 1989). Fos induction has been demonstrated after binding of beta-adrenergic ligands to their cell surface receptors (Barka et al., Mol Cell Biol 6:2984-2989, 1986; Gubits et al., Mol Brain Res 6: 39-45, 1989; Arenander et al., J Neurosci Res 24: 107-114, 1989; Mocchetti et al., Proc Natl Acad Sci USA 86:3891-3895, 1989). However, the response of the jun gene family to this treatment has not been reported. We have therefore examined the effect of beta-adrenergic receptor activation on the expression of c-fos, c-jun, and junB mRNA levels in C6 glioma cells. Our results indicate that c-fos and junB mRNA levels are increased by 52- and 2.7-fold, respectively, after 45 min of isoproterenol (IPR) treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Different members of the jun proto-oncogene family exhibit distinct patterns of expression in response to type beta transforming growth factor.

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.

Characterization of junD: a new member of the jun proto-oncogene family.

In an extensive screen of a cDNA library prepared from serum-stimulated mouse NIH 3T3 cells, we identified three distinct jun-related clones. Two of them were carrying c-jun and junB sequences respectively, whereas the sequence of the third group of clones (junD) was distinct from these two and from v-jun. The amino acid sequences derived from these jun-related clones are very well conserved in five distinct regions including the putative DNA binding domain. Truncated c-Jun and JunD proteins containing the C-terminus recognize the same DNA sequences which were defined as the PEA1/AP1 binding sequence or TPA response element (TRE). Furthermore, both can trans-activate a promoter including the TRE, and this activation is further enhanced by c-fos. Contrary to c-jun and junB transcription, which are strongly stimulated by serum or TPA treatment of quiescent 3T3 cells, junD transcription is not significantly stimulated in these conditions. The tissue distribution and levels of expression of junD mRNA differ from that of c-jun and junB mRNA. These observations suggest that each of these Jun-related gene products has a distinct role in the control of gene activity and growth in the organism.