Protein kinase Cdelta supports survival of MDA-MB-231 breast cancer cells by suppressing the ERK1/2 pathway.
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.
Lønne
Gry Kalstad
GK
Center for Molecular Pathology, Department of Laboratory Medicine, Lund University, and Malmö University Hospital, Sweden.
Masoumi
Katarzyna Chmielarska
KC
Lennartsson
Johan
J
Larsson
Christer
C
D017209:Apoptosis; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D015536:Down-Regulation; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D000075702:Nedd4 Ubiquitin Protein Ligases; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D014162:Transfection; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D056827:Endosomal Sorting Complexes Required for Transport; D034741:RNA, Small Interfering; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; D044767:Ubiquitin-Protein Ligases; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3