DNMT3A/miR-129-2-5p/Rac1 Is an Effector Pathway for SNHG1 to Drive Stem-Cell-like and Invasive Behaviors of Advanced Bladder Cancer Cells

SIMPLE SUMMARY: Bladder cancer ranks fourth among the most prevalent cancers in men and is the most expensive cancer to treat on a per-patient basis. The muscle-invasive form of bladder cancer is one of the deadliest cancers, with a 5-year survival rate of only 6% in patients with distant metastasis. Effective therapeutic options remain few and far between. SNHG1 is a long non-coding RNA that is over-expressed in 95% of muscle-invasive bladder cancers. However, very little information is available about the role and mechanisms of SNHG1 in bladder tumor formation and progression. Here, we provide experimental evidence establishing that SNHG1 drives bladder cancer cell invasion and stem-cell-like behaviors through a specific signaling pathway. Our results reveal novel biomarkers predictive of the progression of muscle-invasive bladder cancer and potential new targets for therapeutic intervention. ABSTRACT: The stem-cell-like behavior of cancer cells plays a central role in tumor heterogeneity and invasion and correlates closely with drug resistance and unfavorable clinical outcomes. However, the molecular underpinnings of cancer cell stemness remain incompletely defined. Here, we show that SNHG1, a long non-coding RNA that is over-expressed in ~95% of human muscle-invasive bladder cancers (MIBCs), induces stem-cell-like sphere formation and the invasion of cultured bladder cancer cells by upregulating Rho GTPase, Rac1. We further show that SNHG1 binds to DNA methylation transferase 3A protein (DNMT3A), and tethers DNMT3A to the promoter of miR-129-2, thus hyper-methylating and repressing miR-129-2-5p transcription. The reduced binding of miR-129-2 to the 3′-UTR of Rac1 mRNA leads to the stabilization of Rac1 mRNA and increased levels of Rac1 protein, which then stimulates MIBC cell sphere formation and invasion. Analysis of the Human Protein Atlas shows that a high expression of Rac1 is strongly associated with poor survival in patients with MIBC. Our data strongly suggest that the SNHG1/DNMT3A/miR-129-2-5p/Rac1 effector pathway drives stem-cell-like and invasive behaviors in MIBC, a deadly form of bladder cancer. Targeting this pathway, alone or in combination with platinum-based therapy, may reduce chemoresistance and improve longer-term outcomes in MIBC patients.