The p53 target Plk2 interacts with TSC proteins impacting mTOR signaling, tumor growth and chemosensitivity under hypoxic conditions.
Tuberous sclerosis complex 1 (TSC1) inhibits mammalian target of rapamycin (mTOR), a central promotor of cell growth and proliferation. The protein product of the TSC1 gene, hamartin (referred to as TSC1) is known to interact with Polo-like kinase 1 (Plk1) in a cell cycle regulated, phosphorylation-dependent manner. We hypothesized that the p53 target gene, Plk2, is a tumor suppressor, mediating its tumor suppressor function through interactions with TSC1 that facilitate TSC1/2 restraint of mTOR under hypoxic stress. We found that human lung tumor cells deficient in Plk2 grew larger than control tumors, and that Plk2 interacts with endogenous TSC1 protein. Additionally, C-terminal Plk2-GST fusion protein bound both TSC1 and TSC2 proteins. TSC1 levels were elevated in response to Adriamycin and cells transiently overexpressing Plk2 demonstrated decreased phosphorylation of the downstream target of mTOR, ribosomal protein p70S6 kinase during hypoxia. Plk2 levels were inversely correlated with cytoplasmic p70S6K phosphorylation. Plk2 levels did not increase in response to DNA damage (Adriamycin, CPT -11) when HCT 116 and H460 cells were exposed to hypoxia. TSC1-deficient mouse embryonic fibroblasts with TSC1 added back demonstrated decreased S6K phosphorylation, which was further decreased when Plk2 was transiently overexpressed. Interestingly, under normoxia, Plk2 deficient tumor cells demonstrated increased apoptosis in response to various chemotherapeutic agents including CPT -11 but increased resistance to apoptotic death after CPT-11 treatment under hypoxia, and tumor xenografts comprised of these Plk2-deficient cells were resistant to CPT -11. Our results point to a novel Plk2-TSC1 interaction with effects on mTOR signaling during hypoxia, and tumor growth that may enable targeting Plk2 signaling in cancer therapy.
Matthew
Elizabeth M
EM
Laboratory of Molecular Oncology and Cell Cycle Regulation, Department of Medicine, The Institute for Translational Medicine and Therapeutics, and Abramson Comprehensive Cancer Center, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Hart
Lori S
LS
Astrinidis
Aristotelis
A
Navaraj
Arunasalam
A
Dolloff
Nathan G
NG
Dicker
David T
DT
Henske
Elizabeth P
EP
El-Deiry
Wafik S
WS
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005260:Female; D006085:Graft Survival / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D014183:Transplantation, Heterologous; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
D000970:Antineoplastic Agents; D047908:Intracellular Signaling Peptides and Proteins; D011993:Recombinant Fusion Proteins; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C496126:PLK2 protein, human; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases