Protein kinase Cδ is required for ErbB2-driven mammary gland tumorigenesis and negatively correlates with prognosis in human breast cancer

Abstract

Protein Kinase C delta (PKCδ) regulates apoptosis in the mammary gland, however the functional contribution of PKCδ to the development or progression of breast cancer has yet to be determined. Meta-analysis of ErbB2-positive breast cancers shows increased PKCδ expression, and a negative correlation between PKCδ expression and prognosis. Here we present in vivo evidence that PKCδ is essential for the development of mammary gland tumors in a ErbB2-overexpression transgenic mouse model, and in vitro evidence that PKCδ is required for proliferative signaling downstream of the ErbB2 receptor. MMTV-ErbB2 mice lacking PKCδ (δKO) have increased tumor latency compared to MMTV-ErbB2 wild type (δWT) mice, and tumors show a dramatic decrease in Ki-67 staining. To explore the relationship between PKCδ and ErbB2-driven proliferation more directly, we used MCF-10A cells engineered to express a synthetic ligand-inducible form of the ErbB2 receptor. Depletion of PKCδ with shRNA inhibited ligand-induced growth in both 2D (plastic) and 3D (Matrigel) culture, and correlated with decreased phosphorylation of the ErbB2 receptor, reduced activation of Src, and reduced activation of the MAPK/ERK pathway. Similarly, in human breast cancer cell lines in which ErbB2 is overexpressed, depletion of PKCδ suppresses proliferation, Src, and ERK activation. PKCδ appears to drive proliferation through formation of an active ErbB2/PKCδ/Src signaling complex, as depletion of PKCδ disrupts association of Src with the ErbB2 receptor. Taken together, our studies present the first evidence that PKCδ is a critical regulator of ErbB2-mediated tumorigenesis, and suggest further investigation of PKCδ as a target in ErbB2-positive breast cancer.

A Kinase Inhibitor Screen Reveals Protein Kinase C-dependent Endocytic Recycling of ErbB2 in Breast Cancer Cells

“…Recent clinical correlative studies also suggest that overexpression of PKC-␣ is associated with poor prognosis in breast cancer (100 -102). PKC-␦ is also known to be overexpressed in a subset of breast cancers and meta-analysis of expression data revealed its specific association with poor survival in ErbB2ϩ breast cancer (98). The same study also established that PKC-␦ gene knock-out delayed tumor development in MMTV-ErbB2 transgenic mice by reducing cellular proliferation.…”

“…A previous study examining the mechanism of estrogen-induced Erk activation in MCF7 breast cancer cell line implicated an autocrine loop involving HRG1 activation of ErbB2; in this system, Erk activation appeared to be mediated by PKC-␦ (97). More recently, PKC-␦ was shown to mediate Erk activation from ErbB2 in ErbB2-overexpressing breast cancer cell lines and PKC-␦ gene knock-out delayed oncogenesis in an ErbB2 transgenic mouse model (98). These findings pointed to PKC-␦ as a potential mediator of PMA-induced Erk activation in our system.…”

Protein kinase C: perfectly balanced

“…PKCδ, which has roles both in survival and apoptotic pathways (Brodie and Blumberg 2003; Griner and Kazanietz 2007; Reyland 2007; Basu and Pal 2010), has been reported to promote tumor progression in pancreatic cancer (Mauro et al 2010), and mice deficient in this isozyme have an increased incidence of lung tumors (Symonds et al 2011). Reyland and colleagues have shown that elevated PKCδ mRNA levels negatively correlate with prognosis in Erb2-positive breast cancer, with mouse models suggesting that it is required for ErbB2-driven mammary gland tumorigenesis (Allen-Petersen et al 2014). Elevated PKCδ mRNA has also been reported to correlate with poor survival outcome in estrogen receptor-positive breast cancer (McKiernan et al 2008; Gyorffy et al 2010).…”

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

“…In contrast to the pro-apoptotic function demonstrated in most non-transformed cells, numerous studies demonstrate a role for PKCδ in cancer cell proliferation and survival. Likewise, PKCδ has been shown to function as a tumor promoter in most (but not all) mouse models of cancer studied (Mauro et al, 2010; Symonds et al, 2011; Allen-Petersen, Carter, Ohm, & Reyland, 2014). Changes in PKCδ expression have been reported in some human tumors (Kahl-Rainer, Karner-Hanusch, Weiss, & Marian, 1994; D’Costa et al, 2006; Reno et al, 2008; Fukase et al, 2011) and increased PKCδ expression correlates with poor prognosis in specific subtypes of human breast cancer (McKiernan et al, 2008; Allen-Petersen et al, 2014).…”