TMIC-14. DIFFUSE P16INK4A EXPRESSION IS ASSOCIATED WITH TUMOR CELL SENESCENCE AND SENESCENCE-ASSOCIATED SECRETARY PHENOTYPE RELATED TO IMMUNE MICROENVIRONMENT IN GLIOBLASTOMAS

Abstract Cellular senescence (CS) is a state of irreversible cell cycle arrest, and the expression of p16INK4a in cells is one of the reliable markers for CS. However, senescent cells are metabolically active with the senescence-associated secretory phenotype (SASP), which can influence the tissue microenvironment by paracrine signaling to the adjacent tumor, non-tumor, and immune cells. In the present study, we evaluated p16INK4a expression in glioblastoma and investigated its association with CS and SASPs. We analyzed the expression of p16INK4a in 73 glioblastomas by immunostaining. To examine the association of p16INK4a expression and CS, we performed senescence-associated β-galactosidase (SA-β-Gal) staining, a standard marker of CS, using glioblastoma cell lines and fresh frozen tumor tissues. For SASPs analysis, RNA sequencing with Gene Set Enrichment Analysis (GSEA) was performed. Among 73 glioblastomas, twenty-eight cases (38.4%) revealed diffuse strong p16INK4a expression in tumor cells. The glioblastoma with diffuse p16INK4a expression (GMDP) patients were younger (52.4 vs. 59.2 years) and showed prolonged overall survival (median: 25.5 vs. 12.3 months) compared to those harboring negative expression. In vitro analysis, p16INK4a over-expressed glioblastoma cell line showed increased expression of SA-β-Gal which indicates CS. In addition, fresh frozen tissues from GMDP also revealed SA-β-Gal positivity. RNA sequencing analysis revealed that splicing or protein biosynthetic genes were enriched in GMDP, and GSEA showed significant enrichment of SASP genes (false discovery rate < 0.05), especially chemokines associated with monocytes and macrophages. Our data suggest that increased expression of p16INK4a in glioblastoma is associated with tumor cell senescence, and SASPs from senescent tumor cells could be one of the crucial modulators in the tumor immune microenvironment.