Abstract 1544: The lncRNA SNHG1 modulates quiescence and chemoresistance of prostate cancer

Abstract Prostate cancer dormancy and chemoresistance contributes to long term morbidity and mortality from this disease. The long non-coding RNA (lncRNA) SNHG1 is highly expressed in prostate cancer and is associated with poor progression-free survival. We investigated SNHG1 involvement in cell cycle regulation, quiescence, and chemoresistance. Suppression of SNHG1 expression using RNAi in PC3 and C4-2B prostate cancer cells resulted in a cessation of proliferation. SNHG1-deficient cells maintained viability, but did not increase in numbers over 7 days post-siRNA transfection. Control cells (siCTRL), meanwhile, expanded 12 and 10-fold, respectively. Analysis of DNA synthesis by EdU staining PC3 cells showed 32% EdU+ siCTRL, but only 7.0% EdU+ siSNHG1, cells. Likewise, C4-2B cells had reduced EdU staining after SNHG1 RNAi. We then analyzed cell cycle and apoptosis in C4-2B, Du145, and LNCaP cells by propidium iodide (PI) staining. Following SNHG1 RNAi, no significant increase in apoptosis or cell cycle arrest was observed, compared to controls. The reduction in S-phase cells was analogous to EdU staining, and there was a modest decrease in G2 phase cells. To investigate quiescence, we knocked down SNHG1 in PC3 cells engineered to express the fluorescent markers Venus and mCherry concurrently with expression of CDT1 and p27, as a marker of G0-phase cells. In SNHG1-deficient cells, 48% were in G0 phase (Venus+, mCherry+), while 13% of siCTRL cells were in G0 phase, indicating that loss of SNHG1 expression blocked cells from exiting G0 and entering the cell cycle. In C4-2B, knockdown of SNHG1 resulted in a 4-5-fold increase in p27(Kip1) expression by immunoblot, indicating increased numbers of quiescent cells. We assessed induction of apoptosis following docetaxel treatment in SNHG1-deficient cells. We found that 20 nM docetaxel induced a 2.9 and 11-fold increase in PARP cleavage in siCTRL-transfected PC3 and C4-2B cells compared to untreated, respectively. When SNHG1 was suppressed by RNAi, PARP cleavage following docetaxel treatment changed by 0.58 and 3.6-fold in PC3 and C4-2B cells, respectively. In addition, we found caspase 3 cleavage after docetaxel treatment was reduced following SNHG1 knockdown, compared to controls. These data indicate cells deficient in SNHG1 are more resistant to docetaxel. Because docetaxel also induced a G2 arrest, we quantified G2 phase by PI staining for DNA content, and immunoblotting for cyclin B1, a marker of G2/M, in siCTRL and siSNHG1 cells. There was a complete elimination of the docetaxel-induced G2 arrest in cells deficient in SNHG1. These data show that SNHG1 plays a role in prostate cancer cell cycle, which has an impact on response to chemotherapy. SNHG1-deficient cells accumulated in G0 phase, and there was reduced apoptosis and resistance to G2 arrest following docetaxel treatment. This is consistent with a model whereby low SNHG1 expression maintains dormancy and protects cells from treatment. Citation Format: Steven P. Zielske, Frank C. Cackowski. The lncRNA SNHG1 modulates quiescence and chemoresistance of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1544.