Vasopressin-activated calcium-mobilizing (VACM-1) protein is a cul-5 gene product that forms complexes with a subclass of ubiquitin E3 ligases involved in proteasomal protein degradation. The expression of VACM-1 cDNA in the T47D breast cancer cell line inhibits growth and decreases phosphorylation of mitogen activated protein kinase. Factors that regulate expression or stability of VACM-1 protein have not been identified, however. In our search to identify drugs/substances that may control VACM-1 protein expression, we examined the effects of resveratrol (trans-3,5,4'-trihydroxystilbene), a natural component in the human diet which inhibits tumor initiation and promotion. CMV vector and VACM-1 cDNA stably transfected T47D breast cancer-derived cells were treated with resveratrol and cell growth and VACM-1 protein concentrations were measured. Since the cellular mechanism of resveratrol-dependent inhibition of cell growth also involves the regulation of estrogen receptors, the effect of 17-β-estradiol and resveratrol on ERα levels and on cell growth was examined in control and in VACM-1 cDNA transfected cells. Our results demonstrate that antiproliferative effect of resveratrol observed in the control T47D cancer cells was significantly enhanced in VACM-1 cDNA transfected T47D cells. Western blot results indicated that resveratrol increased VACM-1 protein concentration. Finally, treatment with resveratrol for 24 and 48 h attenuated 17-β-estradiol induced increase in cell growth both in control and in VACM-1 cDNA transfected cells. The effect was significantly higher in the VACM-1 cDNA transfected cells when compared to controls. These results indicate that the antiproliferative effect of resveratrol may involve induction of VACM-1/cul5.

Vasopressin‐activated calcium‐mobilizing (VACM‐1) receptor, a cul‐5 gene product, has been shown to inhibit cellular growth in the T47D breast cancer cell line through a mechanism that involves MAPK phosphorylation and regulation of estrogen receptor (ERα) concentration. As a cul5 gene product, VACM‐1 protein is involved in ubiquitin ligase dependent protein degradation, but factors that regulate its expression and degradation have not been identified. In our search to identify factors/drugs that control VACM‐1 expression, we studied the effects of resveratrol (3,5,4′‐trihydroxy‐trans‐stilbene) which inhibits cellular functions associated with tumor initiation, promotion, and progression by a mechanism that involves inhibition of MAPK phosphorylation, ERα activation and cell cycle arrest. In our study, control and VACM‐1 cDNA transfected T47D breast cancer cells were treated with reservatol and cell growth and VACM‐1 levels were measured. Our data demonstrate that the dose and time dependent effect of resveratol on cellular proliferation is significantly enhanced in cells transfected with VACM‐1 cDNA. Further, our results indicate that expression of VACM‐1 protein is induced by resveratrol. Consequently, these results indicate that the antiproliferative effect of VACM‐1 can be further enhanced by resveratol. This work was supported by a grant from NCI (R15CA104014) and by Dept of Biology.