Abstract 2226: Loss of STAG2 in bladder cancer

Abstract

Abstract Bladder cancer (BC), 90% of which have transitional cell histology, is the fourth most common malignancy in the US. Transitional cell carcinoma (TCC), which occurs predominantly in men and whose incidence appears to be increasing, occurs most frequently as superficial disease which, while prone to recurrence, is not life threatening. However, TCC which invades the muscle layer of the bladder (stage T2-T4) is lethal in ∼50% of individuals. Stage T2-T4 TCC is present at initial diagnosis in ∼30% of patients and superficial TCC progresses to T2-T4 disease 20% of the time. We sequenced whole exomes of 28 muscle-invasive bladder tumors and performed an additional screen of over 200 genes in 119 additional TCCs. We found frequent alterations (10%) in STAG2, a gene encoding a subunit of the cohesin complex, which regulates the sister chromatids segregation process. Most mutations identified on STAG2 were nonsense, missense or frameshift. Genetic disruption of the sister chromatid segregation process leads to aneuploidy, which is one of the hallmarks of cancer. Based on recently published studies, however, it is uncertain whether a loss of STAG2 causes aneuploidy or not. In this study we sought to elucidate the role of STAG2 loss of expression in bladder tumorigenesis. We have analyzed the expression of STAG2 in 14 urothelial cell lines at both mRNA and protein levels by means of q-PCR and western blots, respectively. We found that STAG2 expression was lost in 2 of the 14 urothelial cell lines (HB-CLS-2 and UM-UC-3) analyzed. We chose SV-HUC (immortalized normal urothelium cells) along with two bladder cancer cell lines that had high expression of STAG2 (HB-CLS-1 and TCC-SUP) to study effects of STAG2 loss by transient knockdown. Knockdown of STAG2 in SV-HUC, TCC-SUP and HB-CLS-1 cells did not affect proliferation. Cell cycle analysis on TCC-SUP cells revealed that STAG2 knockdown resulted in a lower percentage of cells in the G0/G1 phase in comparison to the scrambled control. Taken together, these data suggest that STAG2 has a role in modifying DNA content but not proliferation. Our ongoing studies utilizing bladder cancer tissue microarray (TMAs) and copy number variation (CNV) array will help to clarify the consequences of STAG2 loss in bladder cancer. Citation Format: Nithya Krishnan, Anna Woloszynska-Read, Jianmin Wang, Song Liu, Carl Morrison, Khurshid Guru, Evelyn Smit, Donald Trump, Candace Johnson. Loss of STAG2 in bladder cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2226. doi:10.1158/1538-7445.AM2014-2226