title: Urothelial tumor initiation requires deregulation of multiple signaling pathways: implications in target-based therapies.
abstract: Although formation of urothelial carcinoma of the bladder (UCB) requires multiple steps and proceeds along divergent pathways, the underlying genetic and molecular determinants for each step and pathway remain undefined. By developing transgenic mice expressing single or combinatorial genetic alterations in urothelium, we demonstrated here that overcoming oncogene-induced compensatory tumor barriers was critical for urothelial tumor initiation. Constitutively active Ha-ras (Ras*) elicited urothelial hyperplasia that was persistent and did not progress to tumors over a 10 months period. This resistance to tumorigenesis coincided with increased expression of p53 and all pRb family proteins. Expression of a Simian virus 40 T antigen (SV40T), which disables p53 and pRb family proteins, in urothelial cells expressing Ras* triggered early-onset, rapidly-growing and high-grade papillary UCB that strongly resembled the human counterpart (pTaG3). Urothelial cells expressing both Ras* and SV40T had defective G(1)/S checkpoint, elevated Ras-GTPase and hyperactivated AKT-mTOR signaling. Inhibition of the AKT-mTOR pathway with rapamycin significantly reduced the size of high-grade papillary UCB but hyperactivated mitogen-activated protein kinase (MAPK). Inhibition of AKT-mTOR, MAPK and STAT3 altogether resulted in much greater tumor reduction and longer survival than did inhibition of AKT-mTOR pathway alone. Our studies provide the first experimental evidence delineating the combinatorial genetic events required for initiating high-grade papillary UCB, a poorly defined and highly challenging clinical entity. Furthermore, they suggest that targeted therapy using a single agent such as rapamycin may not be highly effective in controlling high-grade UCB and that combination therapy employing inhibitors against multiple targets are more likely to achieve desirable therapeutic outcomes.
authors.affiliation: Department of Urology, NYU Cancer Institute, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Haiping
authors.initials: H
authors.lastname: Zhou
authors.forename: Hong-ying
authors.initials: HY
authors.lastname: Huang
authors.forename: Ellen
authors.initials: E
authors.lastname: Shapiro
authors.forename: Herbert
authors.initials: H
authors.lastname: Lepor
authors.forename: William C
authors.initials: WC
authors.lastname: Huang
authors.forename: Moosa
authors.initials: M
authors.lastname: Mohammadi
authors.forename: Ian
authors.initials: I
authors.lastname: Mohr
authors.forename: Moon-shong
authors.initials: MS
authors.lastname: Tang
authors.forename: Chuanshu
authors.initials: C
authors.lastname: Huang
authors.forename: Xue-ru
authors.initials: XR
authors.lastname: Wu
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*
chemical_list: D017931:DNA Primers; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D020558:GTP Phosphohydrolases