title: Threonine-120 phosphorylation regulated by phosphoinositide-3-kinase/Akt and mammalian target of rapamycin pathway signaling limits the antitumor activity of mammalian sterile 20-like kinase 1.
abstract: Mst1/Stk4, a hippo-like serine-threonine kinase, is implicated in many cancers, including prostate cancer. However, the mechanisms regulating Mst1 remain obscure. Here, we characterized the effects of phospho-Thr-120 on Mst1 in prostate cancer cells. We demonstrated that phospho-Thr-120 did not alter the nuclear localization or cleavage of Mst1 in a LNCaP or castration-resistant C4-2 prostate tumor cell model, as revealed by a mutagenesis approach. Phospho-Thr-120 appeared to be specific to cancer cells and predominantly localized in the nucleus. In contrast, phospho-Thr-183, a critical regulator of Mst1 cell death, was exclusively found in the cytoplasm. As assessed by immunohistochemistry, a similar distribution of phospho-Mst1-Thr-120/Thr-183 was also observed in a prostate cancer specimen. In addition, the blockade of PI3K signaling by a small molecule inhibitor, LY294002, increased cytoplasmic phospho-Mst1-Thr-183 without having a significant effect on nuclear phospho-Mst1-Thr-120. However, the attenuation of mammalian target of rapamycin (mTOR) activity by a selective pharmacologic inhibitor, Ku0063794 or CCI-779, caused the up-regulation of nuclear phospho-Mst1-Thr-120 without affecting cytoplasmic phospho-Mst1-Thr-183. This suggests that PI3K and mTOR pathway signaling differentially regulate phospho-Mst1-Thr-120/Thr-183. Moreover, mutagenesis and RNAi data revealed that phospho-Thr-120 resulted in C4-2 cell resistance to mTOR inhibition and reduced the Mst1 suppression of cell growth and androgen receptor-driven gene expression. Collectively, these findings indicate that phospho-Thr-120 leads to the loss of Mst1 functions, supporting cancer cell growth and survival.
authors.affiliation: Department of Medicine and Biomedical Sciences, Samuel Oschin Comprehensive Cancer Institute, Los Angeles, California 90048, USA.
authors.forename: Filiz Kisaayak
authors.initials: FK
authors.lastname: Collak
authors.forename: Kader
authors.initials: K
authors.lastname: Yagiz
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Luthringer
authors.forename: Bahriye
authors.initials: B
authors.lastname: Erkaya
authors.forename: Bekir
authors.initials: B
authors.lastname: Cinar
mesh_terms: D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009025:Morpholines / Q000494:pharmacology; D009374:Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D014183:Transplantation, Heterologous; D047368:Tumor Burden; D000099317:Hippo Kinases
chemical_list: D002867:Chromones; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011743:Pyrimidines; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D013912:Threonine; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C401859:temsirolimus; C541932:Ku 0063794; C546842:MTOR protein, human; C095566:STK4 protein, human; D000099317:Hippo Kinases