The jun and fos protein families are both required for cell cycle progression in fibroblasts

Basal expression of the inducible transcription factors c-Jun, JunB, JunD, c-Fos, FosB, and Krox-24 in the adult rat brain

Jun, Fos, and Krox proteins are inducible transcription factors contributing to the control of gene expression. The elucidation of their individual expression patterns in the nervous system provides new insights into the ability of neurons to react with changes of gene expression to external stimulation under physiological or pathological conditions. The expression of c-Jun, JunB, JunD, c-Fos, FosB, and Krox-24 was investigated in the brain of untreated male Sprague-Dawley and female BDIX rats by immunocytochemistry using specific antibodies. JunD immunoreactivity (IR) labeled the highest number of neurons, being present in almost all neurons of the brain. JunD was expressed at high levels in those areas that also exhibit c-Jun, JunB, c-Fos, and FosB-IR, such as locus coeruleus, periolivary nuclei (ncl.), pontine and central gray, lateral lemniscal ncl., inferior and superior colliculi, leaflet of geniculate ncl., midline nuclei of thalamus, dorsomedial and paraventricular ncl. of hypothalamus, ncl. supraopticus, dorsolateral part of caudate putamen and lateral septal ncl. In contrast to the high number of JunD-positive neurons, c-Jun, JunB, c-Fos, and FosB proteins were detected in rather low numbers of neurons in these brain areas; the rank of the number of immunopositive neurons was c-Fos > JunB > c-Jun > FosB. Particularly high levels of expression were observed for c-Jun in medullary motoneurons, medial geniculate ncl., arcuate ncl., and dentate gyrus, and for JunB in the CA-1 area of the hippocampus and islands of Calleja. The zinc finger protein Krox-24 was expressed in many neurons of these brain areas, with only discrete Jun- and Fos-IR; additionally, many intensely labeled nuclei were present in spinal ncl. of the trigeminal ventromedial ncl. of the hypothalamus and the CA-1 area of the hippocampus. In the cerebellum, nuclear labeling was detected only for c-Jun, JunD, and Krox-24 in granule cells. JunD-IR was also found in glial cells of gray matter and fiber tracts, whereas glial c-Jun-IR was observed only in fiber tracts. Apart from a weak JunD-IR, some areas did not express Jun, Fos, and Krox proteins such as cuneate and gracile ncl., venterobasal complex of thalamus, globus pallidum, and Purkinje cells of the cerebellum. Our data indicate that inducible transcription factors of the fos, jun, and krox gene families show patterns of individual expression in untreated animals, thereby reflecting different mechanisms and/or thresholds for induction under physiological conditions.

Reactive oxygen intermediates (ROIs) are involved in the intracellular transduction of angiotensin II signal in C2C12 cells

Increasing evidence suggests that angiotensin II may act as a growth factor for several muscle cell types. Angiotensin II stimulation activates many immediate early response genes like c-Fos, c-Jun, c-Myc and Egr-1 in both vascular smooth muscle cells and cardiomyocytes, independently of whether a hyperplastic or hypertrophic response is taking place. In this study we report that angiotensin II significantly stimulates AP1-driven transcription in mouse skeletal muscle cells C2C12 stably transfected with a TRE-tk-CAT plasmid in a dose-dependent manner (peak stimulation at 10(-5) M of angiotensin II). Moreover, angiotensin II increases the binding of the AP1 complex to its DNA target in both quiescent C2C12 myoblasts and in differentiated C2C12 myotubes. Most of the TRE-bound complexes in both unstimulated and angiotensin II-treated cells consist of c-jun/c-fos heterodimers. Using a set of different protein kinase inhibitors, including HA1004, H7, tyrphostin, genistein and staurosporine, we could demonstrate that the angiotensin II-induced AP1 binding increase is not mediated by the cAMP-dependent pathway and that protein kinase C and tyrosine kinases are involved. Treatment of C2C12 cells with H2O2 induces a dose-dependent increase in c-jun/c-fos heterodimer binding, specifically reverted by the cysteine derivative and glutathione precursor N-acetyl-L-cysteine (NAC). The observation that the induction by angiotensin II of both the AP1 DNA binding activity and DNA synthesis in quiescent C2C12 myoblasts is abolished by NAC strongly suggests a role for reactive oxygen intermediates (ROIs) in the intracellular transduction of angiotensin II signals for immediate early gene induction and for cell proliferation.

In vivo protein-DNA interactions at the c-jun promoter in quiescent and serum-stimulated fibroblasts

c-Jun is an important component in the regulation of cell proliferation. As a member of the early response gene family, c-jun is induced within minutes in the presence of mitogenic agents such as serum growth factors. Using in vivo footprinting, we have analyzed protein-DNA interactions at the c-jun promoter in human fibroblasts subjected to growth arrest and serum stimulation. We located seven footprints upstream of the transcription initiation site. Protein-DNA interactions were detected at two AP-1-like sequences, A CCAAT box, an SP-1 sequence, an NF-jun sequence, a putative RSRF (related to serum response factor) binding site, and a sequence bound by an unknown factor. All of these binding sites were occupied in serum-starved cells, and no additional protein-DNA interactions were detected upon serum stimulation. Evidence from this study supports a model in which expression of the c-jun gene is mediated by phosphorylation events taking place on the transactivation domains of promoter-bound transcriptional activators.

Two distinct signalling pathways are involved in the control of the biphasic junB transcription induced by interleukin-6 in the B cell hybridoma 7TD1

We have measured the level of junB mRNA in the B hybridoma cell line 7TD1, under interleukin-6 (IL-6) stimulation. IL-6 increases junB mRNA in a biphasic fashion. The first early-induced peak was transient and likely corresponds to the well documented typical junB mRNA, stimulated in response to numerous growth factors, including IL-6. At variance, the second peak which has never been reported previously, lasted several hours. As a consequence of its effect on junB mRNA, IL-6 stimulated, in a biphasic fashion, the nuclear accumulation of the JunB protein. In this study, we demonstrated that IL-6 regulation occurred exclusively at the transcriptional level and that the bimodal increase of junB mRNA and JunB protein can be accounted for by a biphasic stimulation of junB transcription. Furthermore, our data point to two major differences between the mechanism of control of the early and the late IL-6-induced junB transcription waves. First, cycloheximide strongly potentiated the transcription of the second wave, whereas it failed to affect the early-induced burst. Second, tyrphostin, a tyrosine kinase inhibitor, impaired the expression of the first but not the second junB mRNA peak. Conversely, genistein, another tyrosine kinase inhibitor, totally abolished the expression of the second peak of junB mRNA whereas it did not affect the expression of the first peak. Altogether these data indicate that, in 7TD1 cells, IL-6 controls junB transcription in a biphasic fashion by means of two separate transduction pathways.

Identification and partial characterization of the c-jun oncogene in Xenopus laevis

Sequencing analysis of a 275-nt cDNA fragment encoding the DNA-binding region at the carboxyl terminal of the Xenopus c-jun protein product shows that this region exhibits 77-79% nucleotide homology and 93% amino acid homology with the DNA-binding region of mouse and human c-jun, and contains an intact leucine zipper motif and a basic DNA-binding region. Xenopus c-jun mRNA is induced in quiescent Xenopus A6 kidney cells by 12-O-tetradecanoylphorbol-13-acetate, PDGF and cycloheximide. This 'immediate early' response suggests that Xenopus c-jun may be similar in both structure and function to that observed for its mammalian counterpart.

Second messenger signaling of c-fos gene induction by parathyroid hormone (PTH) and PTH-related peptide in osteoblastic osteosarcoma cells: its role in osteoblast proliferation and osteoclast-like cell formation

The present study was performed to clarify second messenger signaling in parathyroid hormone (PTH)-induced c-fos gene expression, to characterize the participation of the c-fos gene in the regulation of osteoblast proliferation and function as well as osteoclast-like cell formation by PTH and to compare these effects of PTH with those of PTH-related peptide (PTHrP). Both human (h) PTH-(1-34) and hPTHrP-(1-34) at 10(-8) M induced a transient c-fos gene expression to a similar degree in osteoblastic osteosarcoma cells, UMR-106. N6,O2'-dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP) as well as Sp-diastereoisomer of adenosine cyclic 3',5'-phosphorothioate (Sp-cAMPS), an activator of cAMP-dependent protein kinase (PKA), induced a weak c-fos gene expression. Although Rp-diastereoisomer of adenosine cyclic 3',5'-phosphorothioate (Rp-cAMPS), an inhibitor of PKA, almost completely antagonized dbCAMP- and Sp-cAMPS-induced expression of c-fos gene, it did not cause an obvious inhibition of PTH- or PTHrP-induced expression. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), induced an intense expression of the c-fos gene, while 4 alpha-phorbol 12,13-didecanoate (4 alpha PDD), incapable of activating PKC, and calcium ionophores (A23187 and ionomycin) did not. Protein kinase C inhibitor (H-7, 50 microM) completely blocked the expression of the c-fos gene by PTH as well as by PTHrP). Antisense oligodeoxynucleotides (as-ODN) complementary to c-fos mRNA, which have been shown to inhibit its mRNA translation, at 1 microM significantly antagonized PTH- and PTHrP-induced inhibition of [3H] thymidine incorporation and stimulation of osteoclast-like cell formation in the presence of osteoblasts, but not an increase in alkaline phosphatase activity, compared to control oligodeoxynucleotides with same nucleotides as as-ODN but with a random sequence. The present study indicates the involvement of PKC system in c-fos gene expression by PTH as well as PTHrP and also indicates the involvement of the c-fos gene in the regulation of bone cell physiology by PTH and PTHrP.

The transcription factor CREB is not phosphorylated at serine 133 in axotomized neurons: implications for the expression of AP-1 proteins

The present study has investigated whether nerve fiber transection alters the phosphorylation of serine at position 133 (Ser133) of the transcription factor CREB (phosphoCREB). Activation of CREB by phosphorylation has a major function in the control of gene transcription. PhosphoCREB was visualized by antisera that specifically react with an epitope comprising the phosphorylated Ser133 of CREB as well as of CREM and ATF1 proteins. In untreated rats, nuclear immunoreactivity (IR) of phosphoCREB was consistently visible, e.g. in the cortex, thalamic and hypothalamic compartments and central termination areas of primary somatosensory afferents. Transection of peripheral (sciatic nerve), cranial (hypoglossal and facial nerve) and central (medial forebrain bundle and mammillo-thalamic tract) nerve fibers did not increase phosphoCREB-IR in the axotomized neurons between 5 min and 30 days post-axotomy. In contrast, phosphoCREB-IR appeared after 24 h in glial cells adjacent to the axotomized motoneurons and persisted up to 4 weeks. This increase in glial phosphoCREB-IR was paralleled by enhanced expression of the CREB protein itself. Between 20 min and 24 h following sciatic nerve transection, the number of phosphoCREB labeled nuclei also increased in neurons of the ipsilateral superficial dorsal horn of lumbar L3-L5 spinal cord segments. These data suggest that phosphorylation of Ser133 in CREB/CREM/ATF1 proteins is not involved in the transcriptional control of early-response genes such as c-jun in axotomized neurons following nerve transection. This is in contrast to the reported phosphorylation of CREB and its trans-acting effects on immediate-early genes such as c-fos after transynaptic neuronal excitation.

Developmental expression of the mouse c-rel proto-oncogene in hematopoietic organs

We have studied the expression of the c-rel proto-oncogene during mouse embryonic development and adult animals using in situ hybridization and immunocytochemical analysis. c-rel transcripts were detected late in development with an expression pattern that parallels the emergence and diversification of hematopoietic cells. In the embryo, c-rel is expressed first in the mesoderm-derived hematopoietic cells of the liver and later also in other hematopoietic tissues such as thymus and spleen. This correlation between c-rel expression and places of hematopoietic infiltration is conserved in the postnatal period, with expression of c-rel mRNA in the medullary region of the thymus and in splenic B cell areas, including the marginal zone and the outer region of the periarterial sheath. High levels of c-rel transcripts were also detected in the splenic germinal centers, lymph nodes and Peyer's patches. Using double immunofluorescence and cell preparations from different embryonic and adult hematopoietic organs, we have defined the pattern and cell types of c-rel expression in different hematopoietic cell lineages and in the stromal cell content of the thymus. By using electrophoretic mobility shift assays, we have also correlated c-Rel expression in spleen with kappa B-binding activity in the form of c-Rel/p50 and c-Rel/p52 heterodimers. The timing and pattern of expression of the c-rel proto-oncogene in the different cell lineages suggest that temporally regulated changes in c-Rel expression may be required for vertebrate hematopoiesis.

Ubiquitin-dependent c-Jun degradation in vivo is mediated by the delta domain

The role of the ubiquitin-dependent proteolysis system in c-Jun breakdown was investigated. Using in vitro experiments and a novel in vivo assay that utilizes molecularly-tagged ubiquitin and c-Jun proteins, it was shown that c-Jun, but not its transforming counterpart, retroviral v-Jun, can be efficiently multiubiquitinated. Consistently, v-Jun has a longer half-life than c-Jun. Mutagenesis experiments indicate that the reason for the escape of v-Jun from multiubiquitination and its resulting stabilization is the deletion of the delta domain, a stretch of 27 amino acids that is present in c-Jun but not in v-Jun. c-Jun sequences containing the delta domain, when transferred to the bacterial beta-galactosidase protein, function as a cis-acting ubiquitination and degradation signal. The correlation between transforming ability and the escape from ubiquitin-dependent degradation described here suggests a novel route to oncogenesis.

Induction of c-fos and c-jun mRNA at the M/G1 border is required for cell cycle progression

The proto-oncogenes c-fos and c-jun have been shown in numerous model systems to be induced within minutes of growth factor stimulation, during the G0/G1 transition. In this report we use the mitotic shake-off procedure to generate a population of highly synchronized Swiss 3T3 cells. We show that both of these immediate-early, competence genes are also induced during the M/G1 transition, immediately after completion of mitosis. While c-fos mRNA levels drop to undetectable levels within 2 hr after division, c-jun mRNA levels are maintained at a basal level which is approximately 30% maximum throughout the remainder of G1. In order to access the functional significance of these patterns of c-fos and c-jun expression, antisense oligodeoxynucleotides specific to c-fos or c-jun were added to either actively growing Swiss 3T3 cells or mitotically synchronized cells, and their ability to inhibit DNA synthesis and cell division determined. Our results show that treatment of Swiss 3T3 cells with either c-fos or c-jun antisense oligodeoxynucleotides, while actively growing, during mitosis, or in early G1, results in a reduction in ability to enter S and subsequently divide. This was also true if Swiss 3T3 cells were treated during mid-G1 with c-jun antisense oligodeoxynucleotides. These results demonstrate that the regulation of G1 progression following mitosis is dependent upon the expression and function of the immediate-early, competence proto-oncogenes c-fos and c-jun.

Concurrent immediate early gene induction by epileptic seizures in heterotopic cortical grafts and neocortex

Cortical primordia of rat fetuses (gestation day 14) were stereotactically grafted into the rostral striatum of adult recipient rats. After 8 weeks, the transplants had developed into a highly differentiated population of mature neuroectodermal cells. Host rats were then subjected to 15 min of bicuculline-induced epileptic seizures or served as controls. Seizure-elicited immediate early gene (IEG) expression was investigated after various postictal survival times (up to 24 h), using immunocytochemistry with specific antisera against seven IEG encoded proteins (c-FOS, FOS B, c-JUN, JUN B, JUN D, KROX-24, KROX-20). Constitutive IEG expression in intra striatum grafted neocortical neurons was identical to that in the corresponding host neocortex. In particular, abundant KROX-24 and lack of c-JUN expression implies the establishment of synaptic contacts within the graft or with the host circuitry. Postictal expression kinetics of individual IEG encoded proteins within the transplants were strikingly similar to those seen in the neocortex in situ. c-FOS and KROX-24 were most rapidly induced, followed by c-JUN and JUN B, and a more delayed induction of FOS B, JUN D and KROX-20. Apart from a slightly prolonged c-FOS expression in grafts, individual transcription factors remained elevated for different time periods and showed a concurrent decline in transplants and in neocortex in situ. In conclusion, IEG induction in grafts closely paralleled that in the host neocortex but differed from the adjacent striatum which exhibited no c-JUN induction at any time point investigated. These results indicate that following an appropriate differentiation period, heterotopically grafted embryonic cortical neurons respond to extracellular stimuli with changes of gene expression that closely resemble the normal host cortex. This suggests development of a similar molecular phenotype, including proper acquisition and intracellular processing of information.

Expression of nitric oxide synthase and colocalisation with Jun, Fos and Krox transcription factors in spinal cord neurons following noxious stimulation of the rat hindpaw

Expression of nitric oxide synthase (NOS) was investigated in neurons of lumbar spinal cord of adult rats following subcutaneous injection of formalin (FOR) in one hindpaw. NOS was visualized immunocytochemically using a specific antibody and by the NADPH-diaphorase reaction (NDP). In the untreated rat, NOS immunoreactivity (IR) and NDP were present in neurons of the superficial dorsal horn (sDH) predominantly in layers II-III, and in the deep dorsal horn (dDH) predominantly in layer X. Twenty-four hours following FOR, the numbers of neurons labelled for NOS and NDP and the density of NDP containing nerve fiber varicosities significantly increased in sDH of the ipsilateral L3-L4 segments. NOS-IR and NDP gave a rather congruent distribution of labelled neurons in the dorsal horn. In contrast, distinct NOS-IR but not NDP was visible in large diameter motoneurons and in the lateral spinal nucleus. Double labelling demonstrated that in sDH most of the NDP-reactive neurons show a close spatial relationship to fibers and varicosities immunoreactive for substance P and CGRP. These neuropeptides are considered mediators of synaptic input from nociceptive primary afferents. Colocalization of NDP with c-Jun, JunB, JunD, c-Fos, FosB and Krox-24 transcription factors was investigated in neurons of lumbar spinal cord. c-Jun, JunB, c-Fos and Krox-24 reached their maximal levels of expression 2 h after FOR and returned to basal levels after 10 h. FosB and JunD reached their maximal expression after 5 h, persisted up to 10 h and were still visible in 60%-70% of the maximal number of labelled nuclei after 24 h. This persistent expression of transcription factors might contribute to the up-regulation of NOS expression between 10 h and 24 h. In a low number of NDP neurons, suprabasal immunoreactivity of JunB, c-Fos and Krox-24 proteins was visible up to 10 h, and of JunD and FosB up to 24 h in sDH neurons; c-Jun was not expressed in NDP labelled neurons of sDH, but, similar as JunD, showed basal colocalization in preganglionic sympathetic and parasympathetic neurons. In dDH, colocalization of Jun, Fos and Krox-24 proteins in few neurons was only observed following a second FOR stimulus given 24 h after the first one. Double-staining also demonstrated that many Jun, Fos and Krox labelled neurons are in close proximity to NDP labelled nerve fibers suggesting a functional relationship between expression of immediate-early gene encoded transcription factors and presence of nitric oxide in the rat spinal cord.

c-fos and jun gene expression in murine precursor B lymphocytes developed in the interleukin-7-dependent bone marrow cell culture

We analyzed the expression of c-fos and jun family gene in murine pre-B cells developed in the interleukin-7-(IL-7) dependent bone marrow cell culture. The c-fos gene was expressed in the pre-B cells. The c-fos RNA became undetectable after IgM+ B cells were developed in the culture. The c-fos expression in the pre-B cells was IL-7-dependent. However, the c-fos RNA was not induced when the pre-B cells cultured without IL-7 for 6 h were restimulated with IL-7. The expression of c-jun RNA was slightly induced in the restimulated pre-B cells. The junB and junD RNA were the steady state level in the cells. These gene products formed AP-1 molecule in the pre-B cells. These results suggest that the AP-1 plays a role in the IL-7-dependent pre-B cell development.

Effects of gravity on the cellular response to epidermal growth factor

EGF and related polypeptides are involved in the regulation of cell growth and differentiation of continuously regenerating tissues, in tissue repair processes and in placental and fetal development. Their initial mode of action generally constitutes binding to specific plasma membrane localized receptors, transduction of the signal across the plasma membrane, subsequent activation of signalling pathways in the cell, and the induction of early nuclear gene expression. EGF-induced signal transmission from the plasma membrane to the nucleus has been studied in microgravity in order to gain insight in the molecular mechanisms that constitute the effects of gravity on cell growth. Exposure of human A431 cells to microgravity strongly suppresses EGF- and PMA-induced c-fos and c-jun expression. In contrast, forskolin- and A23187-induced c-fos expression and constitutive beta-2 microglobulin expression remain unaffected. This suggests that microgravity differentially modulates EGF-induced signal transduction pathways. Since both EGF and PMA are known to be activators of PKC, which is not the case for forskolin and A23187, PKC-mediated signal transduction may be a cellular target for microgravity. Inhibition of EGF-induced c-fos expression by microgravity occurs downstream of the initiation of EGF-induced signal transduction, i.e., EGF binding and EGFR redistribution. In addition to PKC signaling, actin microfilament organization appears to be sensitive to microgravity. Therefore, the inhibition of signal transduction by microgravity may be related to alterations in actin microfilament organization. The fact that early gene expression is affected by agents that alter the organization of the actin microfilament system supports this hypothesis. The decrease in c-fos and c-jun expression in microgravity may result in the decreased formation of the FOS and JUN proteins. Consequently, a short-term reduction in gene expression in microgravity may have a more dramatic effect over the long term, since both the JUN and FOS protein families are required for normal cell cycle progression. However, since more than 20 years of manned spaceflight have shown that humans can survive in microgravity for prolonged periods, it appears that cells in the human body can partly or completely overcome gravitational stress. Although some insight in the molecular basis on human cells has been obtained, future studies will be needed for a better understanding of the grounds for alterations in the cellular biochemistry due to altered gravity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of c-jun oncogene expression in human breast using a new monoclonal antibody, NCL-DK4

A new monoclonal antibody to human c-jun oncoprotein, designated NCL-DK4, has been produced. NCL-DK4 has been proved to be highly effective for use on formalin-fixed, paraffin-embedded tissues, enabling the study of c-jun expression at a cellular level in both normal and neoplastic human tissues. The expression of c-jun oncogene has been examined in normal, benign, and malignant breast tissues, and c-jun-specific immunoreactivity in carcinomas has been related to histological type, tumour grade, c-erbB-2, oestrogen receptor, progesterone receptor, and epidermal growth factor receptor expression. Normal and benign breast tissues showed c-jun-specific immunostaining, which was weaker and in fewer cells compared with the c-jun immunoreactivity observed in breast carcinomas. No relationship was found between the degree of immunostaining and the extent of proliferative changes in benign breast tissues. Ninety per cent of all breast carcinomas studied showed c-jun-specific nuclear staining. There were no statistically significant differences in the intensity of c-jun immunoreactivity among grade I, II, and III infiltrating ductal carcinomas. There was no significant relationship between c-jun oncoprotein expression and c-erbB-2, oestrogen, progesterone, and epidermal growth factor receptor immunoreactivity.

Identification of serum-inducible genes: different patterns of gene regulation during G0-->S and G1-->S progression

We have identified, by differential cDNA library screening, 15 serum inducible genes in the human diploid fibroblast cell line WI-38. The genes fall into two classes that are distinguished by their dependence on protein synthesis for the induction by serum, i.e., primary and secondary genes. While 11 of these genes encode known proteins, 4 other genes have not been described to date. The former genes encode proteins of diverse functions, including the monocyte-derived neutrophil chemotactic factor (MONAP), calmodulin, tropomyosin, tenascin, collagenase, plasminogen activator inhibitor-2a, the ‘sperm-specific’ cleavage signal-1 protein, metallothionein IIa and the mitochondrial chaperonin hsp-60. Interestingly, one of the unknown genes contains a large open reading frame for a polypeptide that is highly homologous to a previously unidentified long open reading frame in the opposite strand of the gene coding for the transcription factor HTF-4. We also studied the regulation of these serum-induced genes during cell cycle progression in normally cycling WI-38 and HL-60 cells separated by counterflow elutriation as well as in serum-stimulated HL-60 cells. Our results clearly show that, in contrast to the prevailing opinion, the expression of most genes induced after mitogen stimulation is not subject to a significant regulation in normally proliferating cells. This supports the hypothesis that the progression into S from either G0 or G1 are distinct processes with specific patterns of gene expression.

Transforming growth factor-beta inhibits rat intestinal cell growth by regulating cell cycle specific gene expression

Transforming growth factor-beta 1 (TGF-beta 1) inhibits the growth of intestinal cells, but the mechanisms involved are unknown. Using a rat intestinal crypt cell line (IEC-6), we determined the site of action in the cell cycle that TGF-beta 1 acts to suppress proliferation. We also examined the effect of TGF-beta 1 on the expression of proliferation-associated "immediate early" genes (zif268, jun-B, c-myc) during the early G1 phase and the cdc2 gene during the transition from the G1 phase to the S phase of the cell cycle. Cell cycle progression was determined by incorporation of 3H-thymidine, and gene expression was analyzed by Northern blot analysis. We found that TGF-beta 1 acts to inhibit proliferation of rat intestinal crypt cells by blocking cell cycle progression at the middle G1 phase. The genes activated during G1 can be divided into TGF-beta 1 insensitive (zif268, jun-B, and c-myc) and TGF-beta 1 sensitive (the cdc2 gene). TGF-beta 1 suppresses the induction of the cdc2 gene during the G1/S transition without inhibiting the activation of immediate early genes during the early G1 phase.

Modulation of breast cancer progression and differentiation by the gp30/heregulin [correction of neregulin]

In the last decade we have come to understand that the growth of cancer cells in general and of breast cancer in particular depends, in many cases, upon growth factors that will bind to and activate their receptors. One of these growth factor receptors is the erbB-2 protein which plays an important role in the prognosis of breast cancer and is overexpressed in nearly 30% of human breast cancer patients. While evidence accumulates to support the relationship between erbB-2 overexpression and poor overall survival in breast cancer, understanding of the biological consequence(s) of erbB-2 overexpression remains elusive. Our recent discovery of the gp30 has allowed us to identify a number of related but distinct biological endpoints which appear responsive to signal transduction through the erbB-2 receptor. These endpoints of growth, invasiveness, and differententiation te have clear implications for the emergence, maintenance and/or control of malignancy, and represent established endpoints in the assessment of malignant progression in breast cancer. We have shown that gp30 induces a biphasic growth effect on cells with erbB-2 over-expression. We have recently determined the protein sequence of gp30 and cloned its full length cDNA sequence. We have also cloned two additional forms to the ligand, that are believed to be different isoforms. We are currently expressing the different forms in order to determine their biological effects. To elucidate the cellular mechanisms underlying cell growth inhibition by gp30, we tested the effect of this ligand on cell growth and differentiation of the human breast cancer cells which overexpress erbB-2 and cells which express low levels of this protooncogene.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel cis element mediating ligand-independent activation by c-ErbA: implications for hormonal regulation

A novel type of hormone-responsive element (HRE) is described. Unlike classical HREs, this element, RSV-T3RE (found in Rous sarcoma virus-long terminal repeat), mediates strong activation by the c-ErbA alpha thyroid hormone (T3) receptor in the absence of T3, and addition of T3 reverses this response. Whereas both c-ErbA alpha and v-ErbA are potent ligand-independent activators through the RSV-T3RE, c-ErbA beta is not. The RSV-T3RE is recognized and activated by either c-ErbA alpha homodimers or c-ErbA alpha/retinoid X receptor (RXR) heterodimers. Ligand-independent activation by c-ErbA alpha depends on a unique N-terminal activation domain, while the C-terminal activation domain is not absolutely required. Ligand-dependent activation, on the other hand, requires the C-terminal but not the N-terminal activation domain. Upon binding to the RSV-T3RE, c-ErbA alpha assumes a different conformation than when bound to a classical T3RE. c-ErbA alpha is therefore capable of selective deployment of activation domains, dictated both by the HRE with which it interacts and by T3 binding.

The KROX-20 transcription factor in the rat central and peripheral nervous systems: novel expression pattern of an immediate early gene-encoded protein

The KROX-20 protein (also termed EGR-2) is encoded by an immediate early gene cloned by cross-hybridization to the Drosophila melanogaster Krüppel gene. It belongs to a class of transcription factors with zinc finger motifs and binding activity to a transcriptional regulatory DNA element termed the early growth response consensus sequence. In the present study the temporospatial expression of KROX-20 was investigated in the central and peripheral nervous systems of normal rats and after various stimuli known to induce immediate early genes, including epileptic seizures, axotomy, pharmacological treatment with glutamate and alpha-adrenergic receptor antagonists, and peripheral noxious stimulation. Immunocytochemistry was performed with a specific polyclonal antiserum generated against a fusion protein containing KROX-20 sequences. In the central nervous system, KROX-20 protein demonstrated distinct constitutive nuclear expression in specific neuronal subpopulations of the cortex, septum, amygdala, olfactory bulb and hypothalamus. In addition, distinct cytoplasmic immunoreactivity was present in spinal and medullary motoneurons, dorsal root ganglion neurons and a few neuronal cell populations of midbrain and forebrain. In the CNS, KROX-20 was only induced by bicuculline-induced epileptic seizures. Topographically, the postictal increase of KROX-20 levels was restricted to areas with constitutive expression, such as cerebral cortex, fornix and amygdala. Induction of KROX-20 peaked at 4-8 h after onset of seizure activity. No increase in immunoreactivity was observed in the hippocampus, the brain region most severely affected by bicuculline-induced seizures. Transection of central and peripheral nerve fibers did not result in KROX-20 induction in axotomized neurons. However, KROX-20 was induced in Schwann-like cells after transection of the sciatic nerve. In contrast to KROX-20, KROX-24, a related transcription factor of the zinc finger family, was markedly induced in hippocampal and spinal neurons following seizures and peripheral noxious stimulation, respectively, as well as in CNS neurons following axotomy. Our data indicate that KROX-20 represents an immediately early gene product with basal expression in selected neuronal populations of the nervous system and a restricted inducibility after intentional stimuli.

Differential transcription and translation of immediate early genes in the gerbil hippocampus after transient global ischemia

Excitotoxic activation of glutamate receptors is thought to be a key event for the molecular pathogenesis of postischemic delayed neuronal death of CA-1 neurons in the gerbil hippocampus. Glutamate receptor stimulation also causes induction of transcription factors that belong to the class of immediate early genes. We examined the expression of six different immediate early genes in the gerbil hippocampus after transient global ischemia. Comparative analysis of c-fos and Krox-24 expression was carried out in the same animals at the transcriptional and translational level by in situ hybridization and immunocytochemistry. Postischemic synthesis of four additional immediate early gene (IEG)-encoded proteins (FOS-B, c-JUN, JUN-B, and JUN-D) was investigated by immunocytochemistry at recirculation intervals between 1 and 48 h. After 5 min of ischemia, transcription of c-fos and Krox-24 mRNA was induced in all hippocampal subpopulations with peak expression at 1 h after recirculation. In vulnerable CA-1 neurons, increased transcription of c-fos and Krox-24 was not followed by translation into protein. Induction of immediate early gene-encoded proteins was restricted to neuronal populations less vulnerable to brief ischemia and identified neurons that are targets of glutamate receptor-mediated neurotoxicity but that are destined to survive. Our data indicate an asynchronous synthesis and persistence of individual IEG-encoded proteins in these neurons. The staggered induction implies that combinatorial changes of transcription factors allow a differential postischemic regulation of target gene expression both spatially and over time.

c-jun is essential for normal mouse development and hepatogenesis

The proto-oncogene c-jun is the cellular homologue of v-jun, the transforming oncogene of the avian sarcoma virus 17 (ref. 1). c-jun encodes one major component of the AP-1 transcription factor complex and is expressed in many organs during mouse development and in the adult. Because of its rapid induction in cells following growth stimulation and the presence of AP-1 binding sites in the promoter regions of many genes, the c-Jun protein is thought to have important functions in cell proliferation and differentiation. But embryonic stem (ES) cells lacking c-Jun are viable and have a normal in vitro differentiation capacity, although c-Jun appears to be important for growth of teratocarcinomas in vivo. To define the function of c-jun better, targeted ES cells were used to generate mice lacking c-Jun. Here we report that heterozygous mutant mice appear normal, but embryos lacking c-Jun die at mid- to late-gestation and exhibit impaired hepatogenesis, altered fetal liver erythropoiesis and generalized oedema. Interestingly, c-jun-/- ES cells can participate efficiently in the development of all somatic cells in chimaeric mice except liver cells, further suggesting an essential function of c-Jun in hepatogenesis.

Lineage-restricted chromosome translocation in a benign fibrous tumor of the breast

We describe a clonal chromosome rearrangement, t(4;14)(q24-25;q24.3), in a benign fibrous tumor of the breast. This is the first reported cytogenetic analysis of a fibrous tumor of the breast and the first evidence for clonality in these lesions. A combined immunohistochemical/cytogenetic study demonstrated that cells with the clonal translocation were mesenchymal. Epithelial cells, in contrast, had normal chromosomes.

Expression of relB transcripts during lymphoid organ development: specific expression in dendritic antigen-presenting cells

We have studied the expression of the relB gene during mouse development using in situ hybridization and immunocytochemical analysis. The results show that the expression of the relB gene is highly restricted to a subpopulation of cells that colonize the lymphoid tissues and that appear very late during the process of hematopoietic diversification. RNA transcripts of relB are very low or undetectable in early and late embryos. Low relB expression is observed in the thymus at late stages of embryogenesis but rapidly increases after birth. In adult lymphoid tissues, relB is detected in the medullary region of the thymus, the periarterial lymphatic sheaths of the spleen, and the deep cortex of the lymph nodes, which correspond to the regions where T cells of mature phenotype and interdigitating dendritic cells are present. Using double immunofluorescent labeling of thymic cell suspensions, we have identified the interdigitating dendritic cells as the target of RelB expression. These cells are part of a system of antigen-presenting cells that function in the induction of several immune responses, such as, tolerance, sensitization of MHC-restricted T cells, rejection of organ transplants and formation of T-dependent antibodies. Our observations indicate that RelB may play a particular role in the signal transduction pathway that regulate dendritic cell differentiation and its cellular responses.

Transforming growth factor beta 1-induced delay of cell cycle progression and its association with growth-related gene expression in mouse fibroblasts

TGF beta-induced cell cycle progression is relatively slower than that induced by EGF or PDGF-BB. Further, TGF beta delays EGF or PDGF-induced 5-phase entry in C3H 10T1/2 mouse fibroblasts. In accordance with this delay, the induction of mRNA level of 'immediate early genes' such as c-myc, c-fos, c-jun and junB by TGF beta has slower kinetics compared with those of EGF. TGF beta induces c-sis gene, suggesting possible involvement of secondary growth stimulation by PDGF-like proteins. However, anti-PDGF-AB antibody, which was inhibitory to FDGF-BB-induced [3H]thymidine incorporation, did not block TGF beta-induced DNA synthesis. These results first demonstrate that the delay of cell cycle progression by TGF beta is closely associated with the altered regulation of growth-related gene expression in fibroblasts.

Deregulated c-fos modulates IgG2b production of B cells mediated by lipopolysaccharide

We have examined effects of the deregulated c-fos protein on IgG2b production of B cells cultured with lipopolysaccharide (LPS) using splenic B cells from a transgenic line carrying the mouse c-fos gene under the control of the interferon alpha/beta (IFN) inducible Mx promoter (Mx-c-fosD). High c-fos expression was induced in the Mx-c-fosD B cells during the first two days of culture. DNA synthesis and IgG2b production were augmented in the culture. When IFN was added together with LPS, the high c-fos expression was prolonged until day 3 of culture. IgG2b production was remarkably suppressed. However, the production was not suppressed by upregulation of c-fos via exogenous IFN on day 4 of culture. These results suggest a regulatory effect of the c-fos protein on the differentiation of B cells to IgG2b producing cells at a distinct period.

Resolution of multiple AP-1 complexes in HL-60 cells induced to differentiate by 1,25-dihydroxyvitamin D3

Activator protein-1 (AP-1) complex plays a central role in the regulation of both growth and differentiation in many cell types. Monocytic differentiation of HL-60 cells by TPA (12-0-tetradecanoyl phorbol-13-acetate) has been reported to be paralleled by increased AP-1 binding to DNA and by elevated c-jun expression, suggesting transcriptional level of control. We show that two forms of AP-1 complex, designated AP-1/1 and AP-1/2, can be demonstrated in logarithmically growing HL-60 cells, that the exposure of these cells to 10(-8) M 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) results in increased binding of these complexes to the AP-1 DNA element, and that the AP-1 complex can be resolved into at least three forms in differentiated cells. Binding to, or competition with, a mutated form of the AP-1 binding site shows that the most slowly migrating complex (AP-1/3) binds to DNA with greater specificity than do complexes AP-1/1 and AP-1/2, while antibody inhibition and binding studies performed at 37 degrees C indicate that jun proteins predominate in AP-1/2 complexes. Exposure of extracts from differentiated, but not untreated, HL-60 cells to 2 mM ATP increases the prominence of AP-1/3 complexes, and reduces the DNA binding of AP-1/1 complexes. Treatment of the extracts with phosphatases abolishes the binding of AP-1/2 and AP-1/3 to DNA, and increases the binding intensity of AP-1/1. When extracts from differentiated cells are mixed with extracts from undifferentiated cells the AP-1/3 complexes become less prominent, suggesting than an inhibitory activity in undifferentiated cells prevents the formation of AP-1/3 complexes. These studies show the association of multiple forms of AP-1 complex with the mature monocytic phenotype, and suggest several levels of control of monocytic differentiation.

Spatiotemporal induction of immediate early genes in the rat brain after limbic seizures: effects of NMDA receptor antagonist MK-801

Fos, jun and krox belong to multigene families coding for transcription factors. These cellular immediate early genes (IEGs) are thought to be involved in coupling neuronal excitation to changes of target gene expression. Immunocytochemistry with specific antisera was used to assess regional levels of six IEG-encoded proteins (c-Fos, Fos B, Krox-24, c-Jun, Jun B, Jun D) in the rat forebrain after kainic acid-induced limbic seizures. The results demonstrate a complex spatial pattern of IEG induction and/or suppression in limbic and non-limbic structures. The sequence of induction within hippocampal subpopulations was identical for all IEGs investigated, following the order dentate gyrus, CA1 and CA3, and irrespective of different temporal profiles for individual transcription factors. Since Fos and Jun proteins act via homo- and heterodimer complexes at specific DNA sites, our data imply that the postictal combinatorial changes of these dimers allow a sequential and differential regulation of target gene expression in specific forebrain regions. Pretreatment with the non-competitive NMDA receptor antagonist MK-801 did not affect kainate-induced expression of IEGs in the limbic system, indicating that IEG induction in these regions is mediated by high-affinity kainate and AMPA receptors rather than NMDA receptors. In contrast, MK-801 abolished IEG induction in the somatosensory cortex and striatum, suggesting that IEG expression in non-limbic neurons occurs transsynaptically and is mediated by NMDA receptors.

Inhibition of transcription blocks cell cycle progression of NIH3T3 fibroblasts specifically in G1

We have analysed the role of RNA polymerase II-dependent transcription in cell cycle progression. Time-lapse video recording and cytogenetic analysis were used to determine the sensitivity of NIH3T3 cells to the RNA polymerase II inhibitor alpha-amanitin at different stages of the cell cycle. Our results show that alpha-amanitin blocks cells specifically in G1, irrespective of the concentration within the range of 3 to 30 micrograms/ml. This indicates that transcription in G1 is required to overcome a restriction point located in this phase of the cell cycle. In agreement with this conclusion is the requirement for an uninhibited protein synthesis during G1 progression. In addition, the insensitivity of S-phase cells to RNA polymerase II inhibition suggests that the transcription of genes thought to be normally induced during S/G2 is not required for the completion of an ongoing cell cycle. S/G2 progression was however clearly dependent on protein synthesis. This suggests that cells exposed to alpha-amanitin are able to complete their cell cycle because sufficiently high levels of mRNA are present in S/G2 due to basal level transcription, or are left from preceding cell cycles. It is therefore unlikely that transcriptional regulation in S or G2 plays a crucial role in the control of cell cycle progression in NIH3T3 cells.

Serum-stimulated cell cycle progression and stress protein synthesis in C3H10T1/2 fibroblasts treated with sodium arsenite

In this work, we demonstrated that a nonlethal dose of arsenite administered to quiescent C3H10T1/2 fibroblasts can enhance the mitogenic effect of suboptimal concentrations of serum. The mitogenic effect was dependent on the serum concentration and on the time interval between the administration of arsenite and that of serum. This suggests that mitogen sensitivity changes in time after arsenite treatment. It is shown that the concentrations of arsenite that enhance the mitogenic effect of serum also increase the mRNA levels of c-fos, HSP68, and HSP84 and induce the specific synthesis of Heat Shock Proteins (HSPs). The physiological significance of this phenomenon is most likely to counteract the long-term toxic effect of arsenite by early induction of compensation for cell loss.

Distinct patterns of early response gene expression and proliferation in mouse mast cells stimulated by stem cell factor, interleukin-3, or IgE and antigen

Stem cell factor (SCF) is encoded at the Sl locus of the mouse and is the ligand for the c-kit receptor. Recombinant rat SCF164 (rrSCF164) induces proliferation and promotes maturation of mouse mast cells in vitro and in vivo and can also induce c-kit receptor-dependent mouse mast cell degranulation. We now report that in both quiescent and non-quiescent mouse bone marrow-derived cultured mast cells (BMCMC) rrSCF164 induces increased mRNA levels for the "early response genes" c-fos, c-jun and junB but has only slight effects on the expression of junD. Recombinant mouse interleukin-3 (IL-3) also promotes proliferation of both quiescent and non-quiescent BMCMC. However, IL-3 induces increased expression of c-fos and junB only in quiescent BMCMC. Cross-linking of Fc epsilon receptor type I (Fc epsilon RI) on BMCMC by IgE and specific antigen induces a pattern of early gene expression very similar to that induced by rrSCF164. However, BMCMC stimulated through the Fc epsilon RI did not proliferate and, in comparison to control BMCMC, exhibited significantly decreased proliferation in response to rrSCF164 or IL-3. These results indicate that stimulation of BMCMC proliferation by IL-3 or rrSCF164 induces distinct patterns of early response gene expression and suggest that the proliferative effects of these growth factors may be mediated through distinct signal transduction pathways. Our data also point to previously unappreciated similarities between the effects of signaling through the c-kit receptor or the Fc epsilon RI on mast cell expression of fos and jun genes.

Induction and suppression of immediate early genes in specific rat brain regions by the non-competitive N-methyl-D-aspartate receptor antagonist MK-801

The expression pattern of six different immediate early gene-encoded proteins was examined in the rat forebrain after intraperitoneal administration of MK-801, a non-competitive N-methyl-D-aspartate receptor antagonist, at doses of 3 mg/kg and 0.3 mg/kg, respectively. Following MK-801 treatment, the presence of c-FOS, FOS B, KROX-24, c-JUN, JUN B, and JUN D were investigated by immunocytochemistry with specific antisera at different time intervals up to 48 h. Selective induction of all six immediate early genes was found in layer III neurons of the posterior cingulate and retrosplenial cortex. More complex effects were observed in the neocortex: MK-801 did not influence constitutive expression of different FOS and JUN proteins, but caused marked induction of c-FOS, FOS B, JUN B and JUN D, mainly in layer IV, but also in layers V and VI. In contrast, strong neocortical constitutive expression of KROX-24 was almost abolished by MK-801 administration, and replaced by an expression pattern similar to that of FOS and JUN proteins. Subcortical areas such as the hypothalamus and thalamus demonstrated an induction of a subset of immediate early genes (c-fos, fos B, Krox-24, jun B). Injection of MK-801 caused the same distributional pattern of immediate early gene expression irrespective of the dose given, but the extent of changes was stronger after 3 mg/kg, and altered levels of immunoreactivity persisted longer. In many experimental paradigms, immediate early genes are induced by N-methyl-D-aspartate receptor-mediated mechanisms. This induction can readily be blocked by N-methyl-D-aspartate receptor antagonists like MK-801. Our data, however, indicate that MK-801 itself causes immediate early gene expression in specific neuronal populations. In the present study MK-801-elicited expression of immediate early gene-encoded proteins seems to identify reversibly injured neurons, mainly in layer III of the posterior cingulate and retrosplenial cortex. These neurons have previously been shown to be the principal target of N-methyl-D-aspartate receptor antagonist toxicity. Since immediate early gene induction precedes heat-shock protein expression as well as pathomorphological changes, and is induced in additional cortical cell populations, it seems to be a more rapid and more sensitive indicator of non-lethal neuronal injury.

Localization of Fos and Jun proteins in rat aortic smooth muscle cells after vascular injury

The availability of specific reagents to measure gene activity has provided important tools and potential new directions for the study of smooth muscle cell (SMC) proliferation in vivo. In this report, we have measured steady-state mRNA levels of several fos and jun family members in aortic tissue by Northern blotting after vascular injury. In addition, protein products of these genes were analyzed by immunocytochemistry. Within 15 minutes of balloon injury, mRNA levels of c-fos, fosB, c-jun, junB, and junD were elevated severalfold. In contrast, fos-related antigen (fra-1) mRNA showed a delayed onset of expression. The expression kinetics of these immediate early genes was similar to those in cultured cells stimulated to undergo proliferation by growth factors, suggesting that such SMC gene activation in vivo reflects permeation of blood-derived growth factors into the vessel wall or intravascular release of preformed growth factors. Translation of fos and jun genes into immunoreactive products was demonstrated 2 hours after balloon injury with antisera to Fos and Jun proteins. Treating rats with cycloheximide abolished this immunoreactivity. The distribution of Fos and Jun products was concentrated in SMC nuclei at the luminal border of the rat aorta. Such focal expression may have consequences for the initiation of SMC DNA synthesis and migration after vascular injury. Furthermore, the expression of Fos and Jun proteins in SMC after vascular balloon injury may be used as an index of SMC activation under a variety of experimental settings.

Smooth muscle cell immediate-early gene and growth factor activation follows vascular injury. A putative in vivo mechanism for autocrine growth

To understand the molecular events governing smooth muscle cell (SMC) proliferation in vivo, immediate-early gene (IEG) expression was assessed and related to growth factor ligand and receptor mRNA and SMC DNA synthesis after aortic injury. Balloon catheter injury evoked increases in SMC c-myc and thrombospondin (tsp) within 2 hours. The induction of these IEGs was followed by elevated transcripts to platelet-derived growth factor-A (PDGF-A), transforming growth factor-beta 1 (TGF-beta 1) and a basic fibroblast growth factor (bFGF) receptor. Whereas PDGF type-beta receptor mRNA was demonstrated in SMCs from control and balloon-injured aortas, no detectable signal was observed for the PDGF type-alpha receptor. To explore the potential linkage between IEG products and growth factor mRNA expression, cycloheximide was employed to block early protein synthesis after balloon injury. Induction of PDGF-A and TGF-beta 1 was attenuated by cycloheximide, but bFGF induction was unaffected. Moreover, cycloheximide superinduced IEGs and revealed PDGF-B transcripts, which were otherwise undetected. Seven days after aortic injury, a spontaneous increase in c-myc and tsp mRNA was noted. This IEG reactivation was followed 12 hours later by a twofold increase in SMC DNA synthesis. These findings corroborate an autocrine mode of SMC proliferation in vivo and suggest the IEG products may control such growth by stimulating growth factor genes.

Deregulated c-fos augments cell proliferation of B cells mediated by lipopolysaccharide

We have examined effects of the deregulated c-fos protein on the lipopolysaccharide (LPS)-mediated B cell responses using splenic B cells from transgenic lines carrying the mouse c-fos gene under the control of the H-2K (H2-c-fos) and the inducible Mx promoter (Mx-c-fosD). High c-fos expression was induced in Mx-c-fosD B cells by LPS stimulation. DNA synthesis of the B cells from both lines was augmented depending on the amount of exogenous c-fos. This augmentation resulted in the increase of IgM and IgG2b productions in the culture. These results suggest a functional role of c-fos protein in cell cycle progression of the activated B cells.

Pleiotropic effects of a null mutation in the c-fos proto-oncogene

The c-fos proto-oncogene has been implicated as a central regulatory component of the nuclear response to mitogens and other extracellular stimuli. Embryonic stem cells targeted at the c-fos locus have been used to generate chimeric mice that have transmitted the mutated allele through the germline. Homozygous mutants show reduced placental and fetal weights and significant loss of viability at birth. Approximately 40% of the homozygous mutants survive and grow at normal rates until severe osteopetrosis, characterized by foreshortening of the long bones, ossification of the marrow space, and absence of tooth eruption, begins to develop at approximately 11 days. Among other abnormalities, these mice show delayed or absent gametogenesis, lymphopenia, and altered behavior. Despite these defects, many live as long as their wild-type or heterozygous littermates (currently 7 months). These data indicate that c-fos is not required for the growth of most cell types but is involved in the development and function of several distinct tissues.

Use of antisense oligomers to study the role of c-jun in G1 progression

In actively proliferating Swiss 3T3 fibroblasts, expression of the protooncogene c-jun is maximally induced early in G1, immediately after completion of mitosis. Within 2 hours, c-jun mRNA levels drop to a basal amount that is approximately 30% of the maximum. This is maintained throughout the remainder of G1. To access the functional implications of this pattern of c-jun expression, antisense oligomers specific to c-jun were added to either actively proliferating or synchronized Swiss 3T3 cells, and their ability to inhibit DNA synthesis and division was determined. Our results show that if Swiss 3T3 cells are treated with anti-c-jun while actively growing or at any time during G1 after completion of mitosis, they exhibit a reduced ability to enter S-phase and subsequently divide. These results demonstrate that the regulation of G1 progression following mitosis depends on the expression and function of the protooncogene c-jun.

Induction of FOS and JUN proteins after focal ischemia in the rat: differential effect of the N-methyl-D-aspartate receptor antagonist MK-801

FOS and JUN proteins are transcription factors thought to be involved in coupling neuronal excitation to target gene expression. Cortical infarction of consistent size and location was produced by irradiating the rat brain with Xenon light through the intact skull for 20 min following systemic injection of the photo-sensitizing dye, rose bengal. To investigate the time course and distribution pattern of five cellular immediate early gene (IEG)-encoded proteins after focal ischemia, the expression of c-FOS, FOS B, c-JUN, JUN B and JUN D was studied immunocytochemically in sham-operated control animals and at different postischemic time intervals up to 24 h. A separate group of animals was pretreated with the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801. Photochemically induced focal ischemia caused a rapid induction of FOS and JUN proteins in the entire ipsilateral cortex apart from the ischemic focus. Immunoreactivity in the ipsilateral subcortical gray and white matter and in the entire contralateral hemisphere was indistinguishable from control animals. Individual IEG-encoded proteins were sequentially induced with increased levels of immunoreactivity persisting for different time periods up to 24 h. c-FOS, FOS B, c-JUN and JUN B exhibited a characteristic distribution pattern as reflected by different staining intensities in individual cortical layers. The rapid IEG induction in the entire ipsilateral sensorimotor and limbic structure-associated cortices after photochemically induced infarction most likely reflects spreading depression caused by ischemia and mediated by NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

The transcription factor CREB, but not immediate-early gene encoded proteins, is expressed in activated microglia of lumbar spinal cord following sciatic nerve transection in the rat

Expression of CREB, JUN, FOS and KROX-24 proteins was investigated in glial cells of the lumbar spinal cord. In untreated rats, CREB, c-JUN and JUN D were present in glial cells of the ventral and dorsal horn. Following sciatic nerve transection, the number of CREB immunoreactive glial cells increased in both the ipsilateral ventral and dorsal horns between 24 h and 48 h, reached a maximum after 5 days and returned to control levels after 20 days. Counterstaining with Cresyl violet, a general stain of cells, revealed that the increase of CREB positive glial cells was congruent with the increase of the number of glial cells. Staining with GFAP, a marker for astrocytes, showed an increase in intensity of labelling but no change in number of GFAP labelled cells. This indicates a constitutive expression of CREB in activated microglia. The number of glial cells labelled by c-JUN and JUN D did not change, and glial cells were not labelled by FOS and KROX-24 proteins following sciatic nerve transection. These findings demonstrate that proliferation and differentiation of glial cells in vivo can occur in absence of JUN, FOS and KROX proteins.