Urinary bladder cancer is the fifth most common cancer in the U.S. and the most expensive cancer to treat on a per patient basis because of its high incidence of recurrence and the lack of effective, targeted therapeutics. An expected 70,000 patients will be diagnosed with and 15,000 patients will die of urinary bladder cancer in the U.S. this year alone. Despite the high incidence and lack of therapy for bladder cancer, the mechanisms of tumor initiation and progression are largely unknown. The greatest risk factor for bladder cancer is smoking, which promotes malignant transformation of transitional epithelial cells of the bladder by mechanisms involving DNA damage and oncogene activation. Here we provide the first evidence for entirely novel signaling actions of Regulator of G protein Signaling 6 (RGS6) as an essential mediator of p53 induction during genotoxic stress and as a tumor suppressor in bladder. RGS6 is dramatically induced by tumorigenic stimuli including genotoxic stress and oncogene activation. RGS6 functions as an upstream activator of the ATM-p53- apoptosis pathway yet also induces apoptosis, arrests cell proliferation and blocks oncogenic transformation of cells by p53-independent mechanisms. These actions of RGS6 are independent of its canonical function as a heterotrimeric G protein in activator. We previously described a single nucleotide polymorphism in RGS6, which leads to increased RGS6 translation, which is associated with a significant reduction in the risk of bladder cancer in humans, particularly in smokers. Given these findings, it is especially significant that we observed a dramatically accelerated bladder carcinogenesis and loss of p53 induction in RGS6 null mice in response to their treatment with BBN, a DNA-damaging carcinogen derived from tobacco smoke that induces bladder carcinogenesis in mice closely mimicking that observed in the majority of human patients. The robust expression of RGS6 we found in bladder transitional epithelial cells was dramatically lost in patients with invasive bladder cancer. Our central hypothesis, formulated on the basis of compelling preliminary data, is that RGS6 is a novel master regulator of both DNA damage signaling and tumor suppression in bladder.
Three specific aims are proposed: 1) Determine the importance of RGS6 as a tumor suppressor in a mouse model of bladder carcinogenesis and the role of p53 and ARF in its tumor suppressor function, 2) Determine the underlying molecular mechanisms by which RGS6 functions as an upstream modulator of DNA damage signaling and as a tumor suppressor in bladder transitional epithelial cells, and 3) Determine the molecular basis for RGS6 loss in human bladder cancer.
These aims seek to elucidate the role of RGS6 in suppression of bladder tumorigenesis and the underlying mechanisms involved. Loss of RGS6, as observed in human bladder tumors, or its mutational inactivation would be expected to confer tumor cells with a predisposition to aberrant growth and enhanced survival, hallmarks of malignancy. The significance of these studies to human health is great. They will provide new understanding of the pathogenesis of urinary bladder cancer and potentially identify RGS6 as a biomarker for the prognosis or diagnosis of bladder cancer as well as a new therapeutic target for its treatment.

Public Health Relevance

Our central hypothesis is that RGS6 is a novel inducible tumor suppressor in bladder. The significance of these studies to human health is great as they will provide new understanding of the pathogenesis of urinary bladder cancer and potentially identify RGS6 as a biomarker for the prognosis or diagnosis of bladder cancer as well as a new therapeutic target for its treatment.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA161882-07
Application #
8633015
Study Section
Tumor Cell Biology Study Section (TCB)
Program Officer
Watson, Joanna M
Project Start
2012-04-10
Project End
2017-03-31
Budget Start
2014-04-01
Budget End
2015-03-31
Support Year
7
Fiscal Year
2014
Total Cost
$290,011
Indirect Cost
$97,951
Name
University of Iowa
Department
Pharmacology
Type
Schools of Medicine
DUNS #
062761671
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Rorabaugh, Boyd R; Chakravarti, Bandana; Mabe, Nathaniel W et al. (2017) Regulator of G Protein Signaling 6 Protects the Heart from Ischemic Injury. J Pharmacol Exp Ther 360:409-416
Chakravarti, Bandana; Yang, Jianqi; Ahlers-Dannen, Katelin E et al. (2017) Essentiality of Regulator of G Protein Signaling 6 and Oxidized Ca2+/Calmodulin-Dependent Protein Kinase II in Notch Signaling and Cardiovascular Development. J Am Heart Assoc 6:
Ahlers, Katelin E; Chakravarti, Bandana; Fisher, Rory A (2016) RGS6 as a Novel Therapeutic Target in CNS Diseases and Cancer. AAPS J 18:560-72
Yang, Jianqi; Platt, Lance T; Maity, Biswanath et al. (2016) RGS6 is an essential tumor suppressor that prevents bladder carcinogenesis by promoting p53 activation and DNMT1 downregulation. Oncotarget 7:69159-69172
Stewart, Adele; Fisher, Rory A (2015) Introduction: G Protein-coupled Receptors and RGS Proteins. Prog Mol Biol Transl Sci 133:1-11
Stewart, Adele; Maity, Biswanath; Fisher, Rory A (2015) Two for the Price of One: G Protein-Dependent and -Independent Functions of RGS6 In Vivo. Prog Mol Biol Transl Sci 133:123-51
Stewart, Adele; Maity, Biswanath; Anderegg, Simon P et al. (2015) Regulator of G protein signaling 6 is a critical mediator of both reward-related behavioral and pathological responses to alcohol. Proc Natl Acad Sci U S A 112:E786-95
Huang, J; Stewart, A; Maity, B et al. (2014) RGS6 suppresses Ras-induced cellular transformation by facilitating Tip60-mediated Dnmt1 degradation and promoting apoptosis. Oncogene 33:3604-11
Bifsha, Panojot; Yang, Jianqi; Fisher, Rory A et al. (2014) Rgs6 is required for adult maintenance of dopaminergic neurons in the ventral substantia nigra. PLoS Genet 10:e1004863
Stewart, Adele; Maity, Biswanath; Wunsch, Amanda M et al. (2014) Regulator of G-protein signaling 6 (RGS6) promotes anxiety and depression by attenuating serotonin-mediated activation of the 5-HT(1A) receptor-adenylyl cyclase axis. FASEB J 28:1735-44

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