Activation by Tyrosine Phosphorylation as a Prerequisite for Protein Kinase Cζ to Mediate Epidermal Growth Factor Receptor Signaling to ERK

Abstract

The atypical protein kinase Cζ (PKCζ) was recently shown to mediate epidermal growth factor (EGF)-induced activation of extracellular signal-regulated kinase (ERK) in head and neck squamous carcinoma (HNSCC) cells. Here, it is shown that EGF may induce tyrosine phosphorylation of PKCζ in several HNSCC cells, breast carcinoma cells, as well as mouse embryonic fibroblasts. In COS-7 cells overexpressing EGF receptor (EGFR) and PKCζ as a tumor cell model, we show that PKCζ tyrosine phosphorylation by EGF is induced by catalytic activation. Using a loss-of-function mutant of PKCζ, we can show that the tyrosine residue 417 in PKCζ plays an important role in both PKCζ activation and the ability of PKCζ to mediate activation of ERK. The importance of PKCζ in EGF-induced ERK activation can also be shown in several HNSCC and breast carcinoma cell lines as well as in PKCζ-deficient mouse embryonic fibroblasts. In addition, we present several lines of evidence suggesting the physical association of PKCζ with EGFR and the importance of the EGFR tyrosine kinase c-Src and the Src-specific phosphorylation site pY845-EGFR in the tyrosine phosphorylation as well as catalytic activation of PKCζ. This study characterizes PKCζ as a novel mitogenic downstream mediator of EGFR and indicates PKCζ as a therapeutic target in some carcinomas.

Protein Kinase C Zeta Regulates Human Pancreatic Cancer Cell Transformed Growth and Invasion through a STAT3-Dependent Mechanism

“…Furthermore, STAT3 activation was significantly reduced in PKCζ RNAi tumors when compared to NT RNAi tumors (Figure 5B), indicating that PKCζ regulates STAT3 activation in pancreatic cancer cells both in vitro and in vivo. Since PKCζ has also been implicated in the regulation of ERK1/2 activation in cancer and non-cancer cell types [30], [31], [32], [33], we analyzed the effect of PKCζ RNAi on ERK1/2 phosphorylation in human pancreatic cancer cells. Unlike STAT3 phosphorylation, ERK1/2 phosphorylation was not altered by a significant reduction in PKCζ expression (Figures 5A and S3A) suggesting that PKCζ expression does not regulate signaling through the ERK1/2 signaling pathway.…”

“…Phosphatidylinositol-3,4-5-trisphosphate (Ptdins-3,4,5-P3), the product of phosphoinositide 3-kinase, can directly bind and activate PKCζ, and also activates Ptdins-3,4,5-P3-activated phosphoinositide-dependent kinase 1-mediated phosphorylation and activation of PKCζ [40], [41], [42]. In head and neck squamous carcinoma cells, PKCζ is tyrosine phosphorylated and activated by epidermal growth factor receptor [31]. Future studies will investigate whether either of these pathways, both frequently dysregulated in pancreatic cancer, modulates PKCζ signaling in pancreatic cancer cell lines.…”

Protein Kinase C (PKC) Isozymes and Cancer

“…PKC activation by phosphorylation at tyrosine 417 plays an important role in EGF-mediated ERK activation, DNA synthesis, and cell proliferation in HNSCCs [250,251], while depletion of PLC-1 or PI3K enhancer may abolish EGFmediated SCC cell proliferation [252]. Furthermore, inhibition of PKC can reduce epithelial-mesenchymal transition (EMT), invasion, and migration of oral SCC mediated by the loss of interferon-induced protein with tetratricopeptide repeats 2 (IFIT2) and E-cadherin.…”

Differential regulation of PKD isoforms in oxidative stress conditions through phosphorylation of a conserved Tyr in the P+1 loop

“…Despite the high conservation of the Tyr residue in the P + 1 loop, there are only a few reports of phosphorylation in the YxAPE motif in other kinases. For example, phosphorylation is also reported for PKCδ in oxidative stress conditions 58, 60 and in EGF signaling for PKCε, PKCζ and PKB 8, 61, 62 . Also, the residue was implicated in activation of PKB downstream of RET/PTC 22 .…”