Bryostatin 1 Inhibits Phorbol Ester-Induced Apoptosis in Prostate Cancer Cells by Differentially Modulating Protein Kinase C (PKC) δ Translocation and Preventing PKCδ-Mediated Release of Tumor Necrosis Factor-α

Abstract

Bryostatin 1, a macrocyclic lactone that has been widely characterized as an ultrapotent protein kinase C (PKC) activator, displays marked pharmacological differences with the typical phorbol ester tumor promoters. Bryostatin 1 impairs phorbol 12-myristate 13-acetate (PMA)-induced tumor promotion in mice and is in clinical trials as an anticancer agent for a number of hematopoietic malignancies and solid tumors. In this study, we characterized the effect of bryostatin 1 on LNCaP prostate cancer cells, a cellular model in which PKC isozymes play important roles in the control of growth and survival. Although phorbol esters promote a strong apoptotic response in LNCaP cells via PKC␦-mediated release of TNF␣, bryostatin 1 failed to trigger a death effect even at high concentrations, and it prevented PMA-induced apoptosis in these cells. Mechanistic analysis revealed that bryostatin 1 is unable to induce TNF␣ release, and it impairs the secretion of this cytokine from LNCaP cells in response to PMA. Unlike PMA, bryostatin 1 failed to promote the translocation of PKC␦ to the plasma membrane. Moreover, bryostatin 1 prevented PMA-induced PKC␦ peripheral translocation. Studies using a membrane-targeted PKC␦ construct revealed that the peripheral localization of the kinase is a requisite for triggering apoptosis in LNCaP cells, arguing that mislocalization of PKC␦ may explain the actions of bryostatin 1. The identification of an antiapoptotic effect of bryostatin 1 may have significant relevance in the context of its therapeutic efficacy.

Activation of Nuclear Factor κB (NF-κB) in Prostate Cancer Is Mediated by Protein Kinase C ϵ (PKCϵ)

“…Fig. 6A shows that TNF␣ treatment caused the disappearance of PKC⑀ immunoreactivity from the cytosolic (soluble) fraction with a concomitant increase in the particulate fraction, as well established for PMA (31,34).…”

“…Western Blots-Western blot analysis was carried out essentially as described previously (31). Bands were visualized by the ECL Western blotting detection system.…”

“…PKC⑀ was fused at the N terminus to different tags that direct the kinase to plasma membrane, nucleus, cytoplasm, endoplasmic reticulum or mitochondria (31). Remarkably, at similar levels of expression, only myr-PKC⑀, which is targeted to the plasma membrane (31), was capable of inducing IB␣ phosphorylation and degradation, similar to TNF␣ in nontransfected cells (Fig.…”

Loss of PKCδ Induces Prostate Cancer Resistance to Paclitaxel through Activation of Wnt/β-Catenin Pathway and Mcl-1 Accumulation

“…PKCd is activated by genotoxins, oxidative stress, and death receptors, and its inhibition blocks apoptosis induced by a variety of stimuli in many cell types (6). In the case of prostate cancer, most reports indicate that PKCd expression is required to induce apoptosis by anticancer drugs or death receptors (8)(9)(10)(11)(12)(13)(14). Concretely, in a previous report, we documented that PKCd silencing induced apoptosis resistance to phenylethyl isothiocyanate and anti-Fas or paclitaxel treatments in PC3 and LNCaP cells, whereas the overexpression of PKCd improved apoptosis induced by these treatments in PC3 cells.…”

Calcium blockers inhibit cyclosporine A-induced hyperreactivity of vascular smooth muscle cells

“…PKC enhances the contraction of vascular smooth muscle by L-type calcium channel phosporylation. The importance of PKC activation is proven by the fact that phorbol esters, a group of synthetic PKC activators, induce the contraction of vascular smooth muscle (14)(15)(16)(17)(18).…”