Protein Kinase Cδ Supports Survival of MDA-MB-231 Breast Cancer Cells by Suppressing the ERK1/2 Pathway

Katarzyna Chmielarska Masoumi,Johan Lennartsson,Gry Kalstad Lønne,Christer Larsson

doi:10.1074/jbc.m109.036186

Katarzyna Chmielarska Masoumi, Johan Lennartsson + Show 2 more

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https://doi.org/10.1074/jbc.m109.036186

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Abstract

Mechanisms that mediate apoptosis resistance are attractive therapeutic targets for cancer. Protein kinase Cdelta (PKCdelta) is considered a pro-apoptotic factor in many cell types. In breast cancer, however, it has shown both pro-survival and pro-apoptotic effects. Here, we report for the first time that down-regulation of PKCdelta per se leads to apoptosis of MDA-MB-231 cells. Inhibition of MEK1/2 by either PD98059 or U0126 suppressed the induction of apoptosis of PKCdelta-depleted MDA-MB-231 cells but did not support survival of MCF-7 or MDA-MB-468 cells. Basal ERK1/2 phosphorylation was substantially higher in MDA-MB-231 cells than in the other cell lines. PKCdelta depletion led to even higher ERK1/2 phosphorylation levels and also to lower expression levels of the ERK1/2 phosphatase MKP3. Depletion of MKP3 led to apoptosis and higher levels of ERK1/2 phosphorylation, suggesting that this may be a mechanism mediating the effect of PKCdelta down-regulation. However, PKCdelta silencing also induced increased MEK1/2 phosphorylation, indicating that PKCdelta regulates ERK1/2 phosphorylation both upstream and downstream. Moreover, PKCdelta silencing led to increased levels of the E3 ubiquitin ligase Nedd4, which is a potential regulator of MKP3, because down-regulation led to increased MKP3 levels. Our results highlight PKCdelta as a potential target for therapy of breast cancers with high activity of the ERK1/2 pathway.

Highlights

The protein kinase C (PKC) family is divided into three subgroups depending on the structure of the regulatory domain: classical (PKC␣, PKC␤I, PKC␤II, and PKC␥), novel (PKC␦, PKC⑀, and PKC␪), and atypical (PKC␨ and PKC␫/␭) isoforms
We show that PKC␦ silencing per se induces apoptosis of MDA-MB-231 breast cancer cells
Down-regulation of PKC␦ or PKC⑀ Suppresses Growth of MDA-MB-231 Cells—To examine whether individual PKC isoforms are important for growth of breast cancer cells, the effects of PKC down-regulation were studied (Fig. 1)

Summary

Introduction

The PKC family is divided into three subgroups depending on the structure of the regulatory domain: classical (PKC␣, PKC␤I, PKC␤II, and PKC␥), novel (PKC␦, PKC⑀, and PKC␪), and atypical (PKC␨ and PKC␫/␭) isoforms. Contrary to PKC␦, PKC⑀ has generally been assigned prosurvival and anti-tumorigenic effects [16] for most cell types, including breast cancer cells. Inhibition or silencing of PKC⑀ in breast cancer cell lines makes them more susceptible to apoptotic insults (18 –20), and overexpression or activation of PKC⑀ protects against apoptosis [18, 20, 21]. Another class of proteins that regulate survival and death induction is the MAPK family. GACAGUUGAACGUCGAUUUGCAUUG CCGAGUGAAACUCACGGACUUCAAU CCAAGGUGUUGAUGUCUGUUCAGUA UUUCAAAGAGCUUCUCCAGGAUGUC CACAAGUUCGGUAUCCACAACUACA CCACAAGUUCAUGGCCACCUAUCUU GGCUUACCUUAUGCAGAAGCUCAAU UCUUGGUACAUUGCUUGGCUGGCAU UAUUGGUGACAACUAUUUCUGAUCC UUCAAUUGCCAUCUGAAGUUUAUCC ficity MAPK kinases and are inactivated by dephosphorylation of these residues by the dual specificity MKPs [23]

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