title: Maintaining glycogen synthase kinase-3 activity is critical for mTOR kinase inhibitors to inhibit cancer cell growth.
abstract: mTOR kinase inhibitors that target both mTORC1 and mTORC2 are being evaluated in cancer clinical trials. Here, we report that glycogen synthase kinase-3 (GSK3) is a critical determinant for the therapeutic response to this class of experimental drugs. Pharmacologic inhibition of GSK3 antagonized their suppressive effects on the growth of cancer cells similarly to genetic attenuation of GSK3. Conversely, expression of a constitutively activated form of GSK3β sensitized cancer cells to mTOR inhibition. Consistent with these findings, higher basal levels of GSK3 activity in a panel of human lung cancer cell lines correlated with more efficacious responses. Mechanistic investigations showed that mTOR kinase inhibitors reduced cyclin D1 levels in a GSK3β-dependent manner, independent of their effects on suppressing mTORC1 signaling and cap binding. Notably, selective inhibition of mTORC2 triggered proteasome-mediated cyclin D1 degradation, suggesting that mTORC2 blockade is responsible for GSK3-dependent reduction of cyclin D1. Silencing expression of the ubiquitin E3 ligase FBX4 rescued this reduction, implicating FBX4 in mediating this effect of mTOR inhibition. Together, our findings define a novel mechanism by which mTORC2 promotes cell growth, with potential implications for understanding the clinical action of mTOR kinase inhibitors.
authors.affiliation: Authors' Affiliations: Departments of Hematology and Medical Oncology and Pathology, Emory University School of Medicine and Winship Cancer Institute, Atlanta, Georgia.
authors.forename: Junghui
authors.initials: J
authors.lastname: Koo
authors.forename: Ping
authors.initials: P
authors.lastname: Yue
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Gal
authors.forename: Fadlo R
authors.initials: FR
authors.lastname: Khuri
authors.forename: Shi-Yong
authors.initials: SY
authors.lastname: Sun
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001583:Benzoxazoles / Q000494:pharmacology; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000378:metabolism; D044783:F-Box Proteins / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D057809:HEK293 Cells; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008301:Maleimides / Q000494:pharmacology; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D008819:Mice, Nude; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000378:metabolism; D009287:Naphthyridines / Q000494:pharmacology; D055550:Protein Stability; D059748:Proteolysis; D011687:Purines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D023041:Xenograft Model Antitumor Assays; D000225:Adenine / Q000031:analogs & derivatives
chemical_list: D000970:Antineoplastic Agents; D001583:Benzoxazoles; D019938:Cyclin D1; D044783:F-Box Proteins; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D007211:Indoles; D008301:Maleimides; D000076225:Mechanistic Target of Rapamycin Complex 2; D009025:Morpholines; D046912:Multiprotein Complexes; D009287:Naphthyridines; D011687:Purines; D011743:Pyrimidines; D058570:TOR Serine-Threonine Kinases; C553294:1-(4-(4-propionylpiperazin-1-yl)-3-(trifluoromethyl)phenyl)-9-(quinolin-3-yl)benzo(h)(1,6)naphthyridin-2(1H)-one; C530104:CCND1 protein, human; C508146:FBXO4 protein, human; C417521:SB 216763; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; C546842:MTOR protein, human; C000605506:GSK3B protein, human; C000605507:Gsk3b protein, mouse; C572919:PP242; C572449:sapanisertib; D000225:Adenine