title: Hydroxychloroquine Destabilizes Phospho-S6 in Human Renal Carcinoma Cells.
abstract: mTOR inhibitors are used to treat metastatic renal cell cancer (RCC), but most patients eventually become resistant. One possible mechanism for resistance is upregulation of autophagy, a pathway that helps recycle intracellular proteins and promotes cell survival. Hydroxychloroquine (HCQ), a potent autophagy inhibitor used to treat malaria and autoimmune disorders, is currently being studied in the context of cancer treatment. Here, we have investigated the effects of HCQ on three different renal carcinoma derived cell lines. We found that HCQ treatment inhibits RCC cell growth, promotes apoptosis, inhibits mitochondrial oxygen consumption, and increases rates of glycolysis. To understand the molecular mechanism behind these effects, we examined various nodes in the mTOR pathway and compared the effects of HCQ with the effects of the mTOR inhibitor RAD001. A key downstream readout of the pathway, phospho-S6 protein, was inhibited by both HCQ and RAD001. However, the upstream kinase, P70S6K was only inhibited by RAD001 and not HCQ, suggesting that the block by HCQ was downstream of P70S6K. Treatment with the proteasome inhibitor bortezomib restored phospho-S6 levels, suggesting that the reduction of phospho-S6 is caused by increased degradation of phospho-S6, but not total S6. Surprisingly, treatment with other autophagy inhibitors did not exhibit the same effects. Our findings suggest that HCQ causes the down-regulation of phospho-S6 in RCC cell lines via a novel mechanism that is not shared with other autophagy inhibitors.
authors.affiliation: Cancer Biology Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Hyung-Ok
authors.initials: HO
authors.lastname: Lee
authors.affiliation: Cancer Biology Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Aladdin
authors.initials: A
authors.lastname: Mustafa
authors.affiliation: Cancer Biology Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Gary R
authors.initials: GR
authors.lastname: Hudes
authors.affiliation: Cancer Biology Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Warren D
authors.initials: WD
authors.lastname: Kruger
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D000069286:Bortezomib / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D000068338:Everolimus / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006019:Glycolysis / Q000187:drug effects / Q000235:genetics; D006801:Humans; D006886:Hydroxychloroquine / Q000494:pharmacology*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D006886:Hydroxychloroquine; D000069286:Bortezomib; D000068338:Everolimus; C546842:MTOR protein, human; D019893:Ribosomal Protein S6 Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex