Serum responsiveness of the rat PCNA promoter involves the proximal ATF and AP-1 sites

Testicular localization of activating transcription factor 1 and its potential function during spermatogenesis

Activating transcription factor 1 (ATF1), belonging to the CREB/ATF family of transcription factors, is highly expressed in the testes. However, its role in spermatogenesis has not yet been established. Here, we aimed to elucidate the impact of ATF1 in spermatogenesis by examining the expression pattern of ATF1 in mice and the effect of ATF1 knockdown in the mouse testes. We found that ATF1 is expressed in various organs, with very high levels in the testes. Immunohistochemical staining showed that ATF1 was localized in the nuclei of spermatogonia and co-localized with proliferating cell nuclear antigen. In ATF1-deficient mice, the seminiferous tubules of the testis contained cells at all developmental stages; however, the number of spermatocytes was decreased. Proliferating cell nuclear antigen expression was decreased and apoptotic cells were rare in the seminiferous tubules. These results indicate that ATF1 plays a role in male germ cell proliferation and sperm production.

PLCG2 promotes hepatocyte proliferation in vitro via NF-κB and ERK pathway by targeting bcl2, myc and ccnd1

Phospholipase Cγ2 (PLCG2) has been implicated in the regulation of cell proliferation, transformation, and tumor growth. In this study, we investigate the mechanism of PLCG2 action using a short interference RNA (siRNA) method. The effects of PLCG2 on rat liver BRL-3A cells treated siRNA were studied by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT assay), bromodeoxyuridine (BrdU) labelling assay, flow cytometry method (FCM), quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The results showed when PLCG2 was reduced, cell vitality and proliferation rate were significantly decreased (p < .05 vs. control). FCM analysis showed that the number of cell division phase (G2 + M) was declined (p < .05 vs. control). RT-PCR and western blot revealed that the expression of signalling related genes NF-κB, FOS, JUN and ELK, target genes BCL2, CCNB1 and CCND1 were remarkably down-regulated in cells treated with PLCG2 siRNAs. Based on these results, we conclude PLCG2 plays an important role in rat liver cell proliferation via ERK and NF-κB pathway by regulating the expression of BCl2, MYC and CCND1.

Age-related changes in redox signaling and VSMC function

Epidemiological studies have shown that advancing age is associated with an increased prevalence of cardiovascular disease (CVD). Vascular smooth muscle cells (VSMC) comprise the major arterial cell population, and changes in VSMC behavior, function, and redox status with age contribute to alterations in vascular remodeling and cell signaling. Over two decades of work on aged animal models provide support for age-related changes in VSMC and/or arterial tissues. Enhanced production of reactive oxygen species (ROS) and insufficient removal by scavenging systems are hallmarks of vascular aging. VSMC proliferation and migration are core processes in vascular remodeling and influenced by growth factors and signaling networks. The intrinsic link between gene regulation and aging often relates directly to transcription factors and their regulatory actions. Modulation of growth factor signaling leads to up- or downregulation of transcription factors that control expression of genes associated with VSMC proliferation, inflammation, and ROS production. Four major signaling pathways related to the transcription factors, AP-1, NF-kappaB, FoxO, and Nrf2, will be reviewed. Knowledge of age-related changes in signaling pathways in VSMC that lead to alterations in cell behavior and function consistent with disease progression may help in efforts to attenuate age-related CVD, such as atherosclerosis.

Mitogenic regulation of p27(Kip1) gene is mediated by AP-1 transcription factors

The abundance of cyclin-dependent kinase inhibitor p27(Kip1) during the cell cycle determines whether cells will proliferate or become quiescent. Although the post-translational regulation of p27(Kip1) is well established, its transcriptional regulation is poorly understood. Here, we report that mitogenic stimulation of quiescent HEK293 and Huh7 cells showed a rapid decline in the levels of p27(Kip1) transcript by 2.4 +/- 0.1-fold. Inhibition of the p27(Kip1) gene in response to mitogens involved transcriptional down-regulation and required newly synthesized protein(s). Mutation of the AP-1 element at position -469 in the human p27(Kip1) promoter abrogated the effect of mitogens. The recruitment of the AP-1 complex to the p27(Kip1) promoter was confirmed by in vitro DNA binding and chromatin immunoprecipitation studies. Reporter gene analysis combined with enforced expression of Jun/Fos proteins suggested the involvement of Jun/Fos heterodimer in the transrepression process. Both MAPK and phosphatidylinositol 3-kinase signaling pathways appeared to mediate p27(Kip1) transcription. Furthermore, hepatitis B virus X protein-mediated down-regulation of p27(Kip1) in a transgenic environment correlated with an increase in c-Fos levels, reiterating the physiological relevance of AP-1 in the transcriptional regulation of p27(Kip1). Collectively, our studies present the first evidence demonstrating the role of the AP-1 complex in transcriptional down-regulation of the p27(Kip1) gene following mitogenic stimulation.

Hydrogen sulfide induces serum-independent cell cycle entry in nontransformed rat intestinal epithelial cells

Hydrogen sulfide (H2S), produced by commensal sulfate-reducing bacteria, is an environmental insult that potentially contributes to chronic intestinal epithelial disorders. We tested the hypothesis that exposure of nontransformed intestinal epithelial cells (IEC-18) to the reducing agent sodium hydrogen sulfide (NaHS) activates molecular pathways that underlie epithelial hyperplasia, a phenotype common to both ulcerative colitis (UC) and colorectal cancer. Exposure of IEC-18 cells to NaHS rapidly increased the NADPH/NADP ratio, reduced the intracellular redox environment, and inhibited mitochondrial respiratory activity. The addition of 0.2-5 mM NaHS for 4 h increased the IEC-18 proliferative cell fraction (P<0.05), as evidenced by analysis of the cell cycle and proliferating cell nuclear antigen expression, while apoptosis occurred only at the highest concentration of NaHS. Thirty minutes of NaHS exposure increased (P<0.05) c-Jun mRNA concentrations, consistent with the observed activation of mitogen activated protein kinases (MAPK). Microarray analysis confirmed an increase (P<0.05) in MAPK-mediated proliferative activity, likely reflecting the reduced redox environment of NaHS-treated cells. These data identify functional pathways by which H2S may initiate epithelial dysregulation and thereby contribute to UC or colorectal cancer. Thus, it becomes crucial to understand how genetic background may affect epithelial responsiveness to this bacterial-derived environmental insult.

c-Jun-N-terminal kinase drives cyclin D1 expression and proliferation during liver regeneration

The c-Jun-N-terminal kinase (JNK) pathway is strongly activated after partial hepatectomy (PH), but its role in hepatocyte proliferation is not known. In this study, JNK activity was blocked with the small molecule inhibitor JNK SP600125 in vivo and in vitro as shown by a reduction of c-Jun phosphorylation, AP-1 DNA binding activity, and c-jun messenger RNA (mRNA) expression. SP600125 inhibited proliferating cell nuclear antigen (PCNA) expression, cyclin D1 mRNA and protein expression and reduced mitotic figures after PH. Survival was reduced significantly 3 days after PH in SP600125-treated versus vehicle-treated rats (3 of 11 vs. 8 of 9, P <.01). In epidermal growth factor (EGF)-treated primary cultures of rat hepatocytes, SP600125 decreased (3)H-thymidine uptake, cyclin D1 mRNA and protein expression, and inhibited the EGF-induced transcription of a cyclin D1 promoter-driven reporter gene. The defective regeneration and the decreased survival in SP600125-treated rats did not result from a major increase in apoptosis as shown by normal levels of caspase 3 activity and only slight increases in apoptotic figures. In conclusion, our data show that JNK drives G0 to G1 transition in hepatocytes and that cyclin D1 is a downstream target of the JNK pathway during liver regeneration.

Impaired postnatal hepatocyte proliferation and liver regeneration in mice lacking c-jun in the liver

Mice lacking the AP-1 transcription factor c-jun die at mid-gestation showing heart defects and impaired hepatogenesis. To inactivate c-jun in hepatocytes, mice carrying a floxed c-jun allele were generated. Perinatal liver-specific c-jun deletion caused reduced hepatocyte proliferation and decreased body size. After partial hepatectomy, half of the mutants died and liver regeneration was impaired. This phenotype was not present in mice lacking the N-terminal phosphorylation sites of c-Jun. The failure to regenerate was accompanied by increased cell death and lipid accumulation in hepatocytes. Moreover, cyclin-dependent kinases and several cell cycle regulators were affected, resulting in inefficient G(1)-S phase progression. These studies identify c-Jun as a critical regulator of hepatocyte proliferation and survival during liver development and regeneration.

Genomic structure and regulation of a novel human gene, Klp1

Klp1 (K562 cells-derived leucine zipper-like protein 1) is a transcription factor which binds to the coproporphyrinogen oxidase promoter regulatory element (GGACTACAG). In order to clarify the function of Klp1, we determined the complete human Klp1 genomic structure and regulatory element in the promoter region. The gene spans about 2.4 kb and has three exons. Its promoter region has multiple GC boxes, E2F binding site, one cAMP response element (CRE), and no TATA box with multiple transcription initiation sites, which is characteristic of housekeeping and growth regulating genes. Promoter analysis showed that the promoter was more active in K562 cells entered into the cell cycle by serum stimulation than quiescent cells. Further promoter analysis revealed that CRE at -42 is essential for full promoter activity, and c-Jun and activation transcription factor 1/cAMP response element binding protein 1 proteins bind to this element. These structural characteristics and the promoter function suggest that Klp1 may play a role in cell cycle regulation.