Ras Pathway Activated by Loss of ARL11: A Missing Link in Cancer Initiation.
Sooyoung Lee, Sangkyou Lee, Jolanta Bondaruk, Tadeusz Majewski, Hua Wang, Shizhen Zhang, Menashe Bar-Eli, Peter Black, Yan Wang, Charles C Guo, Colin Dinney, H Barton Grossman, Margaret Knowles, Keith Baggerly, Bogdan Czerniak. UT MD Anderson Cancer Center, Houston, TX; St. James's University Hospital, Leeds, United Kingdom
Background: Our previously reported mapping studies of bladder cancer provided evidence that a new class of genes, referred to as forerunner (FR) genes (ITM2B, P2RY5, GPR38 and ARL11), located near known tumor suppressors such as RB1, drive early clonal expansion of neoplasia. (S Lee, et al. PNAS 104: 13732-13737, 2007) These studies suggested three major steps for the involvement of the RB1 locus in tumor development. In the first step, one allele of FR gene and RB1 is inactivated by deletions. Secondly, homozygous inactivation of the FR genes is accomplished by hypermethylation or less frequently by mutations and is associated with the expansion of early in situ precursor lesions. Finally the contiguous tumor suppressor, such as RB1, is inactivated most commonly by a mutation. This step is associated with clonal evolution into carcinoma in situ progressing to invasive cancer.
Design: Recently, we concentrated our efforts on the ARL11 candidate FR gene, which encodes ADP-ribosylation factor-like 11 protein, a ras-related member of the small GTPases, that functions as GDP/GTP nucleotide interswitch for signal transduction. Our studies focused on ARL11 expression, promoter methylation and cell cycle analysis with emphasis on ARL11's relationship to the ras signaling pathway.
Results: We have shown that ARL11 has been silenced by hypermethylation in approximately 40% of urothelial carcinomas of the bladder and the silencing was associated with in situ expansion of intraurothelial neoplasia. Moreover, loss of ARL11 expression was almost mutually exclusive with the FGFR3 mutations (<5% of bladder tumors showed a co-existence of mutant FGFR3 and methylated ARL11). Functional studies conducted on immortalized normal urothelial cells grown in vitro showed that ARL11 reduced cell proliferation, which was mediated by the inhibition of the ras pathway. This effect was associated with the down-regulation of the active ras and ERK1/2 phosphorylation as well as with the up-regulation of negative cell cycle regulator proteins such as p27kip1 and parallel down-regulation of cyclins D1 and E. Conversely, the silencing of ARL11 conferred a tumor suppressor effect promoting cell proliferation via the activation of the ras signaling pathway.
Conclusions: Recessive events in the RB1 locus associated with the loss of ARL11 promote expansion of intraurothelial precursor lesions by activating the ras pathway in early phases of bladder carcinogenesis.
Category: Genitourinary (including renal tumors)
Tuesday, March 1, 2011 9:30 AM
Poster Session III # 168, Tuesday Morning