Protein kinase C   is a positive modulator of canonical Wnt signaling pathway in tumoral colon cell lines

Abstract

The colonic epithelium is a continuously renewing tissue with a dynamic turnover of cells. Wnt pathway is a key regulator of its homeostasis and is altered in a large proportion of colon cancers. Protein kinase C (PKC) family of serine/threonine kinases are also involved in colon tumor formation and progression; however, the molecular role played by them in the Wnt pathway, is poorly understood. Reciprocal coimmunoprecipitation and immunofluorescence studies revealed that PKCζ interacts with β-catenin mainly in tumoral colon cells, which overexpressed this PKC isoform. The pharmacological inhibition, the small interference RNA-mediated knockdown of PKCζ or the expression of a dominant-negative form of it in tumoral SW480 cells, blocked in a dose-dependent manner the constitutive transcriptional activity mediated by β-catenin, the cell proliferation and the expression of the Wnt target gene c-myc. Remarkably, the PKCζ stably depleted cells exhibited diminished tumorigenic activity in grafted mice. We show that PKCζ functions in a mechanism that does not involve β-catenin degradation since the effects produced by PKCζ inhibition were also obtained in the presence of proteosome inhibitor and in cells expressing a β-catenin degradation-resistant mutant. It was found that PKCζ activity regulates the nuclear localization of β-catenin since PKCζ inhibition induces a rapid export of β-catenin from the nucleus to the cytoplasm in a Leptomycin B sensitive manner. Taken together, our results indicate that the atypical PKCζ plays an important role in the positive regulation of canonical Wnt pathway.

Glycogen Synthase Kinase 3β Is Positively Regulated by Protein Kinase Cζ-Mediated Phosphorylation Induced by Wnt Agonists

“…Recent studies have found that specific interactions between GSK-3␤ and atypical PKC are a key component of the Par complex (15,16) participating in polarity determination. We have recently reported that atypical PKC plays an important role in the positive regulation of the canonical Wnt pathway by controlling nuclear ␤-catenin localization in colon cancer cells (17). In this study, we found that PKC and GSK-3␤ interact specifically mainly in colon cancer cells.…”

“…It is now well known that PKC is one of the key targets of noncanonical Wnt signaling, particularly in the Wnt/ Ca 2ϩ pathway, and we previously demonstrated that PKC plays an important role in the positive regulation of the canonical Wnt pathway by controlling nuclear ␤-catenin localization in colon cancer cells (17).…”

“…In order to confirm that the observed effects were mediated by PKC, we utilized an RNA interference (RNAi) approach to transiently block PKC expression. It is noteworthy that the plasmids utilized were previously constructed and successfully probed by Alex Toker (18), and we also employed these plasmids in a previous study (17). As can be observed in Fig.…”

Protein Kinase C (PKC) Isozymes and Cancer

“…Thus, colon cancer patients with low levels of PKC show a significantly poorer prognosis, compared with patients with higher levels [138]. In contrast, PKC stably depleted SW480 colon cancer cells by decreasing cell proliferation, expression of Wnt target gene c-Myc, and tumorigenic activity in grafted mice [139]. Dexniguldipine hydrochloride (B8509-035) also suppresses the growth of HT-29 cells through the inhibition of PKC expression [140].…”

Atypical Protein Kinase C Signaling in Cancer

“…The role of PKCz in tumorigenesis is somewhat controversial (reviewed in (6)). PKCz has been reported to exhibit tumor-suppressor Authors' Affiliation: Mayo Clinic School of Medicine, Jacksonville, Florida Ó2012 American Association for Cancer Research. activity in human leukemia, colon, breast, ovarian (7), prostate and lung cancer, while other studies have shown PKCz to exhibit pro oncogenic roles in colon (8), human lymphoma (9), prostate, breast, lung, pancreas, and glioblastoma [ Table 1; see also (4,6)]. These contradictory findings will need to be reconciled before PKCz can appropriately be targeted in cancer cells.…”