VACM‐1, a cul‐5 gene product is involved in the ubiquitin ligase complex formation and subsequent protein degradation. When expressed in T47D breast cancer cells, VACM‐1 inhibits growth by inhibiting MAPK phosphorylation (MAPK‐P) and decreasing nuclear estrogen receptors, ERα concentration. Factors that can regulate VACM‐1 protein concentration have not been identified. We have observed that changes in protocol from powder media to a purchased liquid media have led to an increase of endogenous VACM‐1 concentration in control T47D cells. The goal of this project was to examine whether changes in pH will affect VACM‐1 concentration and cell proliferation. Our work has shown that endogenous VACM‐1 protein expression in T47D cells is induced by changes in media pH. Immunocytochemistry data have verified the increased concentration of VACM‐1 in cells grown in liquid media (lower pH) when compared to the powder media (higher pH). The increase in VACM‐1 expression was directly correlated with the decrease in cell growth. These differences were no longer observed when culture media was adjusted to the same pH. These results support the hypothesis that changes in pH may affect VACM‐1 concentrations. This work was supported by a grant from NCI (R15CA104014) and by Dept of Chemistry.