title: AKT upregulates B-Raf Ser445 phosphorylation and ERK1/2 activation in prostate cancer cells in response to androgen depletion.
abstract: Upregulated ERK1/2 activity is often correlated with AKT activation during prostate cancer (PCa) progression, yet their functional relation needs elucidation. Using androgen-deprived LNCaP cells, in which ERK1/2 activation occurs in strong correlation with AKT activation, we found that AKT-mediated B-Raf regulation is necessary for ERK1/2 activation. Specifically, in response to androgen deprivation, AKT upregulated B-Raf phosphorylation at Ser445 without affecting A-Raf or C-Raf-1. This effect of AKT was abolished by Arg25 to Ala mutation or truncating (∆4-129) the pleckstrin homology domain of AKT, indicating that the canonical AKT regulation is important for this signaling. Intriguingly, although a constitutively active AKT containing N-terminal myristoylation signal could sufficiently upregulate B-Raf phosphorylation at Ser445 in LNCaP cells, subsequent MEK/ERK activation still required hormone deprivation. In contrast, AKT activity was sufficient to induce not only B-Raf phosphorylation but also MEK/ERK activation in the hormone refractory LNCaP variant, C4-2. These data indicate that androgen depletion may induce MEK/ERK activation through a synergy between AKT-dependent and -independent mechanisms and that the latter may become deregulated in association with castration resistance. In support, consistent AKT-mediated B-Raf regulation was also detected in a panel of PCa lines derived from the cPten(-/-)L mice before and after castration. Our results also demonstrate that AKT regulates androgen receptor levels partly via the Raf/MEK/ERK pathway. This study reveals a novel crosstalk between ERK1/2 and AKT in PCa cells.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
authors.forename: Seung-Keun
authors.initials: SK
authors.lastname: Hong
authors.affiliation: Department of Dermatology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Jeong
authors.affiliation: School of Biomedical Sciences, Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Chan
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. Electronic address: jipark@mcw.edu.
authors.forename: Jong-In
authors.initials: JI
authors.lastname: Park
mesh_terms: D000728:Androgens / Q000172:deficiency*; D000818:Animals; D045744:Cell Line, Tumor; D006801:Humans; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000201:enzymology*; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism*; D017384:Sequence Deletion; D012694:Serine / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D000728:Androgens; D012694:Serine; C482119:BRAF protein, human; D051058:Oncogene Protein v-akt; D048493:Proto-Oncogene Proteins B-raf; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse