AP-1 (Activating Protein1The members of the Fos, Jun, ATF (Activating Transcription Factor), and MAF (Musculo Aponeurotic Fibrosarcoma) protein families are components of the dimeric AP-1 (Activating Protein 1) transcription factor complex. AP-1 participates in the regulation of a variety of cellular processes, such as cell proliferation, cell differentiation, neoplastic transformation, and apoptosis (Angel and Karin 1991; Karin et al. 1997;Eferl and Wagner 2003). AP-1 transcription factor activity is regulated at multiple levels, including transcriptional control, post-translational modifications, dimer composition, and interactions with many structurally divergent regulatory proteins. AP-1 proteins are prototype transcription factors that harbor several functional domains: (1) several transactivation regions, (2) a basic domain that interacts with sequence elements in the promoters and enhancers of target genes, and (3) the adjacent leucine-zipper domain (ZIP) required for dimerization, a prerequisite for AP-1 DNA-binding activity and for transcriptional regulation of target genes (Angel and Karin 1991;Karin et al. 1997;Eferl and Wagner 2003).The importance of protein-protein interactions in the control of AP-1 function is suitably illustrated by the participation of Fos and Jun in multiple dimeric transcription complexes including: (1) Jun/Jun homodimers, (2) Fos/Jun heterodimers, (3) heterodimers between Fos or Jun and other "basic-ZIP" (bZIP) family proteins (e.g., ATF, MAF, Nrf-1, Nrf-2), and (4)

Resveratrol (RES), a chemopreventive molecule, inhibits the proliferation of tumor cells of different etiologies. We previously showed that RES alters the cell cycle and induces apoptosis in MCF-7 breast tumor cells by interfering with the estrogen receptor (ERa)-dependent phosphoinositide 3-kinase (PI3K) pathway. Here, we analyzed signaling downstream of PI3K, to understand the mechanisms of RES-induced apoptosis. Apoptotic death by RES in MCF-7 was mediated by Bcl-2 downregulation since overexpression of this protein abolished apoptosis. Decreased Bcl-2 levels were not related to cytochrome c release, activation of caspases 3/8 or poly(ADP-ribose) polymerase proteolysis. However, RES decreased mitochondrial membrane potential and increased reactive oxygen species and nitric oxide production. NF-kB, a regulator of Bcl-2 expression, and calpain protease activity, a regulator of NF-kB, were both inhibited by RES. The patterns for NFkB and calpain activities followed that of PI3K and were inhibited by LY294002. NF-kB inhibition coincided with diminished MMP-9 activity and cell migration. These data suggest that RES-induced apoptosis in MCF-7 could involve an oxidative, caspase-independent mechanism, whereby inhibition of PI3K signaling converges to Bcl-2 through NF-kB and calpain protease activity. Therefore, Bcl-2 and NF-kB could be considered potential targets for the chemopreventive activity of RES in estrogen-responsive tumor cells. ' 2005 Wiley-Liss, Inc.Key words: resveratrol; caspase; Bcl-2; NF-kB; apoptosis Among natural compounds with beneficial effects on human health, RES (3,4 0 ,5-trihydroxystilbene) has attracted considerable interest. This molecule, present at relevant concentrations in red wine, 1 has been associated with a lower incidence of cardiovascular disease. Different studies have also suggested a beneficial effect of RES in cancer since it inhibits proliferation and promotes death in tumor cell lines of different origins, 2-4 and, in vivo, suppresses the formation of skin 5 and mammary gland 6 tumors in rodent models of carcinogenesis.We, as well as other laboratories, have found that the ability of RES to inhibit cell viability and proliferation in the human breast cancer cell lines MCF-7 and MDA-MB-231 was unrelated to ERa status. 7,8 However, apoptotic cell death was present only in ERapositive MCF-7 and involved cell-specific regulation of the G 1 /S and G 2 /M transitions of the cell cycle. 2,8 RES properties are related to ERa since this compound has estrogenic or antiestrogenic activities depending on its concentration and the phenotype of the target cell. 9,10 ERa, in addition to its nuclear role as a transcription factor, is involved in regulating the PI3K pathway, which controls cell growth, proliferation and apoptosis. [11][12][13] In MCF-7 cells, RES induced a biphasic pattern of PI3K activity that increased at low concentrations and decreased at high concentrations. Activation of downstream PI3K effectors PKB/AKT and GSK-3 closely followed the pattern of PI3K activity. 14 The ...

SummaryStore-operated calcium entry (SOCE) is an important Ca 2+ entry pathway that regulates many cell functions. Upon store depletion, STIM1, a transmembrane protein located in the endoplasmic reticulum (ER), aggregates and relocates close to the plasma membrane (PM) where it activates store-operated calcium channels (SOCs). Although STIM1 was early defined as a phosphoprotein, the contribution of the phosphorylation has been elusive. In the present work, STIM1 was found to be a target of extracellular-signalregulated kinases 1 and 2 (ERK1/2) in vitro, and we have defined the ERK1/2-phosphorylated sites on the STIM1 sequence. Using HEK293 cells stably transfected for the expression of tagged STIM1, we found that alanine substitution mutants of ERK1/2 target sites reduced SOCE significantly, suggesting that phosphorylation of these residues are required to fully accomplish SOCE. Indeed, the ERK1/2 inhibitors PD184352 and PD0325901 decreased SOCE in transfected cells. Conversely, 12-O-tetradecanoylphorbol-13-acetate, which activates ERK1/2, enhanced SOCE in cells expressing wild-type tagged STIM1, but did not potentiate Ca 2+ influx in cells expressing serine to alanine mutations in ERK1/2 target sites of STIM1. Alanine substitution mutations decreased Ca 2+ influx without disturbing the aggregation of STIM1 upon store depletion and without affecting the relocalization in ER-PM punctae. However, our results suggest that STIM1 phosphorylation at ERK1/2 target sites can modulate SOCE by altering STIM1 binding to SOCs, because a significant decrease in FRET efficiency was observed between alanine substitution mutants of STIM1-GFP and ORAI1-CFP.

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