Abstract 1942: Regulation of GRNMB transcription and cellular effects by chondroitin 4-sulfation

Abstract

Abstract Increased expression of glycoprotein (transmembrane) NMB (GPNMB; osteoactivin) has been identified in triple negative breast cancer, melanoma, glioma, and hepatocellular carcinoma, and followed decline in expression of the enzyme arylsulfatase B (ARSB; N-acetylgalactosamine 4-sulfatase). The expression and regulation of GPNMB was evaluated in HepG2 cells and in ARSB-deficient and control C57BL/6J mouse hepatic tissue. Increased expression of GPNMB was attributable to promoter activation by phospho(Ser)MITF (microphthalmia-associated transcription factor), the phosphorylation of which was activated by phospho(Ser)-p38 MAPK. When ARSB was reduced, nuclear phospho-MITF increased and GPNMB promoter activity increased, as detected by Renilla reniformis luciferase assay. Chromatin immunoprecipitation assay confirmed that phospho-MITF bound to a specific motif in the GPNMB promoter, and binding increased when ARSB was silenced. Up-regulation of promoter activity increased the expression of GPNMB message and the synthesis of GPNMB protein in the HepG2 cells and ARSB-null mouse liver. The tyrosine phosphatase SHP2 bound more tightly to C4S when ARSB was reduced, leading to inhibition of SHP2 activity and reduced removal of phosphate from Tyr182 of phospho-p38 MAPK. The increase in C4S stimulated phospho(Ser)-p38 MAPK by activation of RhoA, leading to MITF phosphorylation and increased GPNMB expression. Silencing GPNMB by siRNA reduced phosphorylation of ERK and expression of matrix metalloproteinase (MMP)-9, consistent with effects on hepatic cell invasiveness. These findings indicate that ARSB-induced changes in chondroitin 4-sulfation impact on critical phosphorylations mediated by SHP2 and p38 MAPK, leading to activation of MITF and increased expression of GPNMB. The interaction between chondroitin 4-sulfation and phosphorylations may regulate vital cell processes, including transcriptional events and cell-matrix interactions. Citation Format: Joanne Kramer Tobacman, Leo Feferman, Sumit Bhattacharyya. Regulation of GRNMB transcription and cellular effects by chondroitin 4-sulfation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1942. doi:10.1158/1538-7445.AM2015-1942