Activation of protein kinase C (PKC)1 isozymes by phorbol esters and related agents induces a plethora of cellular responses, including changes in cell cycle progression, differentiation, survival, and transformation. PKC isozymes comprise a family of related serine-threonine kinases grouped on the basis oftheirstructuralandbiochemicalproperties:"classic"orcalciumdependent PKCs ("cPKCs" ␣, ␤I, ␤II, and ␥), "novel" or calciumindependent PKCs ("nPKCs" ␦, ⑀, , and ) and "atypical" PKCs ("aPKCs" and /). Only the first two groups and the related PKC/protein kinase D are responsive to phorbol esters and to the second messenger diacylglycerol (DAG), the endogenous ligand for these PKCs (1-3). Phorbol ester treatment can either promote mitogenesis or inhibit cell proliferation depending on the cell type. Such heterogeneity is probably related to the multiplicity of cellular targets that mediate their responses, which include not only the PKC isozymes but also novel "nonkinase" phorbol ester receptors such as chimaerins, RasGRP isozymes, and Munc13s (4). Studies on the roles of individual phorbol ester receptors as mediators of mitogenic and survival responses have revealed a high degree of complexity in their downstream effectors. Indeed, within the PKC family some members are capable of stimulating mitogenesis, such as PKC⑀, whereas others such as PKC␦ are preferentially growth inhibitory in most cell types. An emerging theme is that this heterogeneity involves a delicate regulation of signaling pathways by individual PKC isoforms, which is probably related to a distinctive pattern of intracellular compartmentalization and access to targets (1,2,(5)(6)(7)(8).Unlike most cell types, androgen-dependent prostate cancer cells undergo apoptosis in response to phorbol esters (9 -11). The mechanisms underlying this atypical response are still poorly understood. Using multiple pharmacological and molecular approaches, we have previously demonstrated that both the classic PKC␣ and the novel PKC␦ mediate the apoptotic response of phorbol esters in LNCaP androgen-dependent prostate cancer cells. Although in some cell types the pro-apoptotic effect of PKC␦ involves its proteolytic cleavage and subsequent release of an active catalytic fragment, in LNCaP cells it de-

Activation of protein kinase CD (PKCD), a member of the novel PKC family, leads to apoptosis in several cell types. Although the molecular bases of PKCD activation are being unfolded, limited information is available on the mechanisms that control its expression. Here, we report that in prostate cancer cells PKCD is tightly regulated by androgens at the transcriptional level. Steroid depletion from the culture medium causes a pronounced down-regulation of PKCD protein and mRNA in androgen-sensitive LNCaP prostate cancer cells, an effect that is rescued by the androgen R1881 in an androgen receptor (AR)-dependent manner. Analysis of the PKCd promoter revealed a putative androgen responsive element (ARE) located 4.7 kb upstream from the transcription start site. Luciferase reporter assays show that this element is highly responsive to androgens, and mutations in key nucleotides in the AR-binding consensus abolish reporter activity. Furthermore, using chromatin immunoprecipitation assays, we determined that the AR binds in vivo to the PKCD ARE in response to androgen stimulation. Functional studies revealed that, notably, androgens modulate phorbol 12-myristate 13-acetate (PMA)-induced apoptosis in LNCaP cells, an effect that is dependent on PKCD. Indeed, androgen depletion or AR RNA interference severely impaired the apoptotic function of PKCD or the activation of p38, a downstream effector of PKCD in LNCaP cells-effects that can be rescued by restoring PKCD levels using an adenoviral delivery approach. Our studies identified a novel hormonal mechanism for the control of PKCD expression via transcriptional regulation that fine-tunes the magnitude of PKCD apoptotic responses. (Cancer Res 2006; 66(24): 11792-801)

A series of both genetic and epigenetic factors have been implicated in the genesis and progression of prostate cancer. Recent evidence revealed that protein kinase C (PKC) isozymes play a crucial role in the control of cell proliferation and apoptosis in prostate cancer models, as well as in the transition from an androgen-dependent to an androgen-independent status. Indeed, PKCalpha and PKCdelta promote apoptosis in androgen-dependent prostate cancer cells. Due to the relevance of PKC isozymes in the control of cell cycle, both in G1/S and G2/M, the elucidation of such complex intracellular networks using cellular and animal models has become of outmost importance. In this review, we present the current knowledge on the regulation of apoptosis and tumorigenicity by PKC isozymes and the functional roles of cell cycle regulators in prostate carcinogenesis. The development of animal models where overexpression of discrete PKCs or cell cycle regulators is targeted to the prostate will greatly contribute to the understanding of the molecular basis of the disease, and more importantly, it will have profound implications for the development of novel strategies for prostate cancer therapy.