Asymmetric demethylation at histone H3 arginine 2 by PRMT6 in gastric cancer progression (AGS cell line)

Purpose: Dysregulation of histone H3 arginine (R) methylation is still unknown in primary cancer including gastric cancer (GC), although PRMT6 plays a role in asymmetric dimethylation at H3R2 (H3R2me2as) in cancer cells. The objective is to clarify biological and molecular roles of H3R2me2as-PRMT6 pathway in GC. Experimental Design: We assessed H3R2me2as and PRMT6 levels in 133 primary GC tissues by immunohistochemistry. We analyzed biological functions of PRMT6 in GC cell lines using a lentivirus overexpression and CRISPR/Cas9-based knockout of PRMT6 systems. Results: Increased H3R2me2as was found in 68 GC (51.1%) cases and independently correlated with poor prognosis. PRMT6 was overexpressed in 70 (52.6%) GC, which strongly correlated with the H3R2me2as levels (P<0.001). PRMT6 overexpression in GC cells enhanced global H3R2me2as levels, cell invasiveness in vitro, while PRMT6-knockout GC cells suppressed these effects. PRMT6 knockout also impaired tumorigenicity in vivo. Microarray and ChIP assays demonstrated that PRMT6-knockout GC cells decreased the H3R2me2as levels at the promoter regions of PCDH7, SCD and IGFBP5, resulting in up-reregulation of their gene expression. PRMT6 recruited at the regions of PCDH7 and SCD in the PRMT6-overexpressed cells. Knockdown of tumor suppressor PCDH7 in PRMT6-knockout GC cells elevated cell migration and invasion. PRMT6 expression inversely correlated with PCDH7 expression in primary GC (P=0.021). Conclusions: H3R2me2as is a strong prognostic indicator of GC patients. Global and gene-specific H3R2me2as are maintained by PRMT6. PRMT6-overexpressed GC cells may acquire invasiveness through direct inhibition of PCDH7 by increasing H3R2me2as activity. Thus, PRMT6-H3R2me2as pathway is a promising new therapeutic target in GC. PRMT6-knockout gastric cancer cells were established by using a lentiviral CRISPR/Cas9 system.