Role of endoplasmic reticulum calcium content in prostate cancer cell growth regulation by IGF and TNFalpha

Variations in calcium concentration within the endoplasmic reticulum (Ca(2+)](ER)) may play a role in cell growth. This study evaluates the regulation of calcium pools by growth modulators of prostate cancer (PC) cells, the insulin growth factor (IGF), and the tumor necrosis growth factor-alpha (TNFalpha) as well as evaluating the possible role of Ca(2+)](ER) variations as signals for growth modulation. We show that IGF (5 ng/ml), which increases cell growth, induces an increase in Ca(2+)](ER) whereas TNFalpha (1 ng/ml) which reduces cell proliferation and induces apoptosis, reduces Ca(2+)](ER). IGF-induced Ca(2+)](ER) increase is correlated to an overexpression of the sarcoendoplasmic calcium-ATPase 2B (SERCA2b), whereas TNFalpha-induced Ca(2+)](ER) decrease is associated to a reduction in SERCA2b expression. Pretreatment with epidermal growth factors (EGF) or IGF does not prevent TNFalpha from affecting the induction of apoptosis, Ca(2+)](ER) reduction and SERCA2b downregulation. Reduction in Ca(2+)](ER) induced by thapsigargin (TG) (from 1 pM to 1 microM, 48 h) reduces LNCaP growth in a dose dependent manner and induces apoptosis when cells are treated with 1 microM TG. We also show that a transient TG application (1 pM, 1 nM, 1 microM 15 min) is insufficient to induce a long lasting decrease in Ca(2+)](ER), since Ca(2+)](ER) remains identical to the control for 48 h following TG application. These treatments (1 pM and 1 nM, 15 min) do not modify cell growth. However, TG (1 microM, 15 min) induces apoptosis. We thus identify Ca(2+)](ER) and SERCA2b as a central targets for causing LNCaP PC cell life or death induced by growth modulators. Furthermore our results indicate that calcium pool contents can regulate cell growth.