Protein Kinase C Delta Negatively Modulates Canonical Wnt Pathway and Cell Proliferation in Colon Tumor Cell Lines

Abstract

The tumor suppressor Adenomatous Polyposis coli (APC) gene is mutated or lost in most colon cancers. Alterations in Protein kinase C (PKC) isozyme expression and aberrant regulation also comprise early events in intestinal carcinomas. Here we show that PKCδ expression levels are decreased in colon tumor cell lines with respect to non-malignant cells. Reciprocal co-immunoprecipitation and immunofluorescence studies revealed that PKCδ interacts specifically with both full-length (from non-malignant cells) and truncated APC protein (from cancerous cells) at the cytoplasm and at the cell nucleus. Selective inhibition of PKCδ in cancer SW480 cells, which do not possess a functional β-catenin destruction complex, did not affect β-catenin-mediated transcriptional activity. However, in human colon carcinoma RKO cells, which have a normal β-catenin destruction complex, negatively affected β-catenin-mediated transcriptional activity, cell proliferation, and the expression of Wnt target genes C-MYC and CYCLIN D1. These negative effects were confirmed by siRNA-mediated knockdown of PKCδ and by the expression of a dominant negative form of PKCδ in RKO cells. Remarkably, the PKCδ stably depleted cells exhibited augmented tumorigenic activity in grafted mice. We show that PKCδ functions in a mechanism that involves regulation of β-catenin degradation, because PKCδ inhibition induces β-catenin stabilization at the cytoplasm and its nuclear presence at the C-MYC enhancer even without Wnt3a stimulation. In addition, expression of a dominant form of PKCδ diminished APC phosphorylation in intact cells, suggesting that PKCδ may modulate canonical Wnt activation negatively through APC phosphorylation.

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

“…There are several reports that link PKCd with the regulation of the Wnt/b-catenin pathway (16), and other reports link this signaling pathway with Mcl-1 modulation (17)(18)(19). On the basis of these articles, we propose that PKCd would modulate Mcl-1 by regulation of the Wnt/b-catenin pathway in prostate cancer cells.…”

“…PKCd negatively modulates the canonical Wnt/b-catenin pathway (16) and this pathway modulates Mcl-1 expression in several tumor types (17)(18)(19). As we observed a prominent increase of Mcl-1 L in PKCd-silenced cells and this protein has an important role in paclitaxel-induced apoptosis, we examined whether PKCd modulates Mcl-1 expression through the Wnt/b-catenin pathway in prostate cancer cells.…”

Neurokinin-2 receptor polymorphism predicts lymph node metastasis in colorectal cancer patients

“…The study found that activation of NK2R in afferent neurons led to the protein kinase C (PKC)-induced phosphorylation of a certain gene (23). PKCδ was known to negatively modulate the canonical Wnt pathway and cell proliferation in colon tumor cell lines (24). Moreover, the connection between NK2R and PKC was confirmed by another study, which showed that stimulation of NK2R was not only linked to PKC activation, but that it was also associated with the activation of a multidrug resistance protein transporter in vivo (25).…”

Protein Kinase C (PKC) Isozymes and Cancer

“…In colon cancer cells, PKC can inhibit cell growth and proliferation by mediating changes in several cellular signaling pathways by enhancing phosphorylation of APC [142], p53 expression [143,144], and p21…”