Androgens modulate phorbol ester-induced apoptosis and the secretion of pro-apoptotic factors from LNCaP prostate cancer cells Free

5159

It is well established that activation of PKCδ by phorbol esters induces apoptosis in androgen dependent LNCaP prostate cancer cells, an effect that is mediated by the secretion of autocrine death factors and the activation of the extrinsic apoptotic cascade (Gonzalez-Guerrico et al., JBC 280:38982-38991, 2005). Recent studies have shown that the pro-apoptotic activity of PKCδ is dependent on the presence of androgens, which regulate PKCδ expression at the transcriptional level (Gavrielides et al., 2006, Cancer Res., in press). We speculated that the autocrine secretion of death factors, a PKCδ-dependent effect, is regulated by androgens. Conditioned medium (CM) was collected from phorbol 12-myristate 13 acetate (PMA)-treated LNCaP cells (CM-PMA) and assessed for its ability to secrete death factors and induce an apoptotic response in LNCaP cells. Androgen depletion significantly reduced the apoptotic activity of CM-PMA. This effect was reversed by addition of the androgen analogue R1881 to the androgen-depleted medium. Androgen depletion also diminished the ability of the CM-PMA to activate p38, JNK, and caspase-8 as well as to dephosphorylate Akt. The secretion of TNF-α, TRAIL and CCL2 in response to PMA, the three major cytokines contributing to the apoptotic effect of the phorbol ester, was markedly reduced in CM-PMA collected from androgen depleted LNCaP cells both at the mRNA and protein levels, as determined by real-time PCR and ELISA, respectively. These effects were reversed by R1881. Moreover, silencing of the androgen-receptor in LNCaP cells using RNAi significantly reduced the apoptotic effect of CM-PMA, the ability of CM-PMA to activate apoptotic signaling cascades, and the secretion of apoptotic factors to the CM. The androgen depletion effect can be partially rescued by over-expression of PKCδ. These results indicate that the autocrine secretion of pro-apoptotic factors in response to PKC activation is regulated by androgens through it ability to control the expression of PKCδ isozyme.