Members of the bcl-2 gene family encode proteins that function either to promote or to inhibit apoptosis. Despite numerous eorts, the mechanism of action of Bcl-2, an anti-apoptotic protein, is still not clear. In particular, the relation between Bcl-2 and the endoplasmic reticulum (ER) calcium store is not well-understood. In the present work, we examined the eect of Bcl-2 on the ER store. We demonstrate that overexpression of Bcl-2 in breast epithelial cells modulates ER store by upregulating calcium pump (SERCA) expression without aecting the release channel (IP 3 R). The steady state levels of SERCA2 mRNA and protein were both increased in Bcl-2 expression clones. The increase in SERCA2 protein leads to accelerated calcium uptake and enhanced Ca 2+ loading. In addition, we also show the detection of intracellular interaction between Bcl-2 and SERCA molecules by co-immunoprecipitation. Since high lumenal Ca 2+ concentration of ER is essential for normal cell functions, the results suggest that Bcl-2 preserves the ER Ca 2+ store by upregulating SERCA gene expression as well as by a possible interaction with the pump.

Galectin-3 is a multifunctional carbohydrate-binding protein found in the nucleus, cytoplasm and the extracellular milieu. Nuclear galectin-3 expression is associated with cell proliferation, and its role in premRNA splicing has been suggested. In this report, we investigated the role of galectin-3 on cyclin D 1 gene expression, a critical inducer of the cell cycle and a potential oncogene in human cancer. We found that galectin-3 induces cyclin D 1 promoter activity in human breast epithelial cells independent of cell adhesion through multiple cis-elements, including the SP1 and CRE sites. We present evidence that galectin-3 induction of the cyclin D 1 promoter may result from enhancement/ stabilization of nuclear protein-DNA complex formation at the CRE site of the cyclin D 1 promoter. We also show that galectin-3 co-operates with, but does not depend on, pRb for cyclin D 1 promoter activation. The present study reveals a growth promoting activity of galectin-3 through cyclin D 1 induction, and suggests a novel function of nuclear galectin-3 in the regulation of gene transcription.

Many recent studies have focused on potential chemopreventive activities of dietary genistein, a natural isoflavonoid compound found in soy products. Genistein has been implicated in anticancer activities, including differentiation, apoptosis, inhibition of cell growth and inhibition of angiogenesis. In previous studies, genistein was shown to induce apoptosis and cell cycle arrest at G(2)/M in several cancer cell lines in vitro, which is associated with induction of p21(WAF1/CIP1), a universal inhibitor of cyclin-dependent kinases. At present, the molecular basis for diverse genistein-mediated cellular responses is largely unknown. In the present study, we investigated whether galectin-3, an anti-apoptotic gene product, regulates genistein-mediated cellular responses. We show that genistein effectively induces apoptosis without detectable cell cycle arrest in BT549, a human breast epithelial cell line which does not express galectin-3 at a detectable level. In galectin-3 transfected BT549 cells, genistein induced cell cycle arrest at the G(2)/M phase without apoptosis induction. Interestingly, genistein induces p21(WAF1/CIP1) expression in galectin-3-expressing BT549 cells, but not in control BT549 cells undergoing apoptosis. Collectively, the results of the present study suggest that galectin-3, at least in part, is a critical determinant for genistein-mediated cell cycle arrest and apoptosis, and genistein induction of p21(WAF1/CIP1) is associated with cell cycle arrest, but not required for apoptosis induction.