title: RGS6 is an essential tumor suppressor that prevents bladder carcinogenesis by promoting p53 activation and DNMT1 downregulation.
abstract: Urinary bladder cancer (UBC) is largely caused by exposure to toxic chemicals including those in cigarette smoke (i.e. BBN). An activating SNP in RGS6 is associated with a pronounced reduction in UBC risk, especially among smokers. However, the mechanism underlying this reduction remains unknown. Here we demonstrate that RGS6 is robustly expressed in human urothelium, where urothelial cell carcinoma originates, and is downregulated in human UBC. Utilizing RGS6-/- mice we interrogated a possible role for RGS6 as a tumor suppressor using the BBN-induced bladder carcinogenesis model that closely recapitulates human disease. As in humans, RGS6 is robustly expressed in mouse urothelium. RGS6 loss dramatically accelerates BBN-induced bladder carcinogenesis, with RGS6-/- mice consistently displaying more advanced pathological lesions than RGS6+/+ mice. Furthermore, BBN treatment promotes urothelial RGS6 mRNA and protein downregulation. RGS6 loss impairs p53 activation and promotes aberrant accumulation of oncogenic protein DNMT1 in urothelium. Tumor suppressor RASSF1A, a DNMT1-regulated gene, is also silenced, likely via methylation of its promoter during BBN exposure. We hypothesize that this BBN-induced RGS6 loss represents a critical hit in UBC as it irrevocably impairs the anti-proliferative actions of the ATM/p53 and RASSF1A pathways. Consistent with these findings, RGS6-/- mice treated with CP-31398, a p53-stablizing agent, and/or 5-Aza, a DNMT1 inhibitor, are protected from BBN-induced tumorigenesis. Together, our data identify RGS6 as a master tumor suppressor modulating two critical signaling pathways that are often dysregulated in UBC; therefore, RGS6 represents a potential novel biomarker for UBC diagnosis/prognosis and an appealing new target in its treatment.
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Jianqi
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Lance T
authors.initials: LT
authors.lastname: Platt
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Biswanath
authors.initials: B
authors.lastname: Maity
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Katelin E
authors.initials: KE
authors.lastname: Ahlers
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Zili
authors.initials: Z
authors.lastname: Luo
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Bandana
authors.initials: B
authors.lastname: Chakravarti
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Stella-Rita
authors.initials: SR
authors.lastname: Ibeawuchi
authors.affiliation: Department of Pathology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Ryan W
authors.initials: RW
authors.lastname: Askeland
authors.affiliation: Department of Pathology, MD Anderson Cancer Center, the University of Texas, Houston, TX, USA.
authors.forename: Jolanta
authors.initials: J
authors.lastname: Bondaruk
authors.affiliation: Department of Pathology, MD Anderson Cancer Center, the University of Texas, Houston, TX, USA.
authors.forename: Bogdan A
authors.initials: BA
authors.lastname: Czerniak
authors.affiliation: Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Rory A
authors.initials: RA
authors.lastname: Fisher
mesh_terms: D000818:Animals; D002085:Butylhydroxybutylnitrosamine / Q000633:toxicity; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D000076123:DNA (Cytosine-5-)-Methyltransferase 1 / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020710:RGS Proteins / Q000235:genetics* / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism; D019459:Urothelium / Q000187:drug effects / Q000378:metabolism
chemical_list: D020710:RGS Proteins; C400194:RGS6 protein, human; C485692:Rgs6 protein, mouse; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D002085:Butylhydroxybutylnitrosamine; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; C000619381:Dnmt1 protein, mouse
keywords: DNMT1; RGS6; p53; tumor suppressor; urinary bladder cancer