title: The mitogen-activated protein kinase pathway mediates growth arrest or E1A-dependent apoptosis in SKBR3 human breast cancer cells.
abstract: Previously, we have shown that phorbol ester (PMA) induces p21(WAF1/CIP1)-dependent growth arrest in SKBr3 breast cancer and LNCaP prostate cancer cells. Here, I demonstrate that inhibition of Raf-1 kinase by dominant-negative Raf-1 or pharmacological depletion of Raf-1 prevented PMA-mediated induction of p21(WAF1/CIP1). Similarly, PD98059, a specific inhibitor of MEK, abolished p21(WAF1/CIP1) induction and PMA-induced growth arrest. Like PMA, the H-ras oncogene, another activator of the Raf-1/MEK/MAPK pathway, transactivated p21(WAF1/CIP1) in SKBr3 cells. I further investigated PMA-induced growth arrest following infection of SKBr3 cells with 12S E1A-expressing adenovirus. Although high levels of E1A oncoprotein prevented both PMA-induced p21(WAF1/CIP1) and growth arrest, smaller amounts of E1A abrogated growth arrest without down-regulation of p21(WAF1/CIP1). Therefore, E1A can stimulate proliferation downstream of p21(WAF1/CIP1). Albeit less effective than full activity, either Rb- or p300-binding activity of E1A was sufficient for the abrogation of PMA-mediated growth arrest. E1A-driven proliferation of PMA-treated SKBr3 cells was accompanied by apoptosis. New therapeutic approaches can be envisioned that would utilize stimulation of the Raf-1/MEK/MAPK pathway to inhibit growth of PMA-sensitive cancer cells.
authors.affiliation: Medicine Branch, National Cancer Institute, NIH, Bethesda, MD 20892, USA. mikhailb@box-m.nih.gov
authors.forename: M V
authors.initials: MV
authors.lastname: Blagosklonny
mesh_terms: D017500:Adenovirus E1A Proteins / Q000494:pharmacology*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D002273:Carcinogens / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis; D004789:Enzyme Activation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism
chemical_list: D017500:Adenovirus E1A Proteins; C493956:CDKN1A protein, human; D002273:Carcinogens; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D007527:Isoenzymes; D010703:Phorbol Esters; D019908:Proto-Oncogene Proteins c-raf; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D018631:ras Proteins