Cyclin D1 protein expression is regulated by mitogenic stimuli and is a critical component in the regulation of G 1 to S phase progression of the cell cycle. Angiotensin II (Ang II) binds to specific G protein-coupled receptors and is mitogenic in Chinese hamster ovary cells stably expressing the rat vascular Ang II type 1A receptor (CHO-AT 1A ). We recently reported that in these cells, Ang II induced cyclin D1 promoter activation and protein expression in a phosphatidylinositol 3-kinase (PI3K)-, SHP-2-, and mitogen-activated protein kinase/ extracellular signal-regulated kinase (MAPK/ERK)-dependent manner (Guillemot, L., Levy, A., Zhao, Z. J., Bé ré ziat, G., and Rothhut, B. (2000) J. Biol. Chem. 275, 26349 -26358). In this report, transfection studies using a series of deleted cyclin D1 promoters revealed that two regions between base pairs (bp) ؊136 and ؊96 and between bp ؊29 and ؉139 of the human cyclin D1 promoter contained regulatory elements required for Ang II-mediated induction. Mutational analysis in the ؊136 to ؊96 bp region provided evidence that a Sp1/early growth response protein (Egr) motif was responsible for cyclin D1 promoter activation by Ang II. Gel shift and supershift studies showed that Ang II-induced Egr-1 binding involved de novo protein synthesis and correlated well with Egr-1 promoter activation. Both U0126 (an inhibitor of the MAPK/ERK kinase MEK) and wortmannin (an inhibitor of PI3K) abrogated Egr-1 endogenous expression and Egr-1 promoter activity induced by Ang II. Moreover, using a co-transfection approach, we found that Ang II induction of Egr-1 promoter activity was blocked by dominant-negative p21 ras , Raf-1, and tyrosine phosphatase SHP-2 mutants. Identical effects were obtained when inhibitors and dominant negative mutants were tested on the ؊29 to ؉139 bp region of the cyclin D1 promoter. Taken together, these findings demonstrate that Ang II-induced cyclin D1 up-regulation is mediated by the activation and specific interaction of Egr-1 with the ؊136 to ؊96 bp region of the cyclin D1 promoter and by activation of the ؊29 to ؉139 bp region, both in a p21 ras /Raf-1/MEK/ERK-dependent manner, and also involves PI3K and SHP-2.The control of mammalian cell proliferation by extracellular signals in G 1 to S phase progression of the cell cycle is largely mediated by serine/threonine cyclin-dependent kinases CDK4 1 and CDK6, which interact with specific D-type cyclins. The CDK-D-type cyclin complexes induce phosphorylation of the retinoblastoma protein (pRb), thereby releasing the transcription factor E2F, which is required for the transcription of S phase-specific genes (1-4). Activation by mitogenic stimuli of D-type cyclins during the G 1 phase appears to be an essential and rate-limiting step in G 1 to S phase progression of the cell cycle (5-7). The cyclin D1 gene expression seems to be essentially regulated at the transcription level. The promoter region of the cyclin D1 gene contains multiple potential cis-regulatory elements including binding sites for AP1, E2F, Oct, Egr-1...

These results demonstrate that ASU express a unique range of activities, which could counteract deleterious processes involved in OA, such as inflammation.

Clastogenic factors were first described in the plasma of people who had been accidentally or therapeutically irradiated. They were found also in A-bomb survivors, where they persisted for many years after the irradiation. The present study searched for these factors in the plasma of 32 civil workers from Armenia, who had been engaged as "liquidators" around the Chernobyl atomic power station in 1986. It also included 15 liquidators who had emigrated from the ex-Soviet Union to Israel. Reference plasma samples were obtained from 41 blood donors from the Armenian Blood Center in Yerevan. The samples were tested for their clastogenic activity in blood cultures from healthy donors. The majority of results from the liquidators exceeded those from the unexposed reference samples. The samples from the first Armenian group, with the higher average irradiation dose (0.6 +/- 0.6 Gy), were more clastogenic than those from the second group exposed to 0.2 +/- 0.2 Gy. The number of aberrations in the test cultures was 17.9 +/- 2.9% and 10.5 +/- 3.8% respectively, compared to 5.7 +/- 3.2% in the cultures exposed to the reference ultrafiltrates from Armenian blood donors. The samples from the Israeli liquidators also induced significantly increased aberration rates (14.0 +/- 3.9% aberrant cells). The clastogenic activity was regularly inhibited by superoxide dismutase, indicating that the chromosome-damaging effects of radiation-induced clastogenic factors are exerted via the intermediation of superoxide radicals, as is known for clastogenic factors of different origin.