Chondroitin sulfate modification of CSPG4 regulates the maintenance and differentiation of glioma-initiating cells via integrin-associated signaling

Abstract

Glioma stem/initiating cells (GSC/GIC) and their niches are considered responsible for the therapeutic resistance and recurrence of malignant glioma. To clarify the molecular mechanisms of GIC maintenance/differentiation, we performed a unique integrated proteogenomics utilizing GIC clones established from patient tumors having the potential to develop glioblastoma. After the integration and extraction of the transcriptomics/proteomics data, we found that chondroitin sulfate proteoglycan 4 (CSPG4) and its glyco-biosynthetic enzymes were significantly upregulated in GICs. Glyco-qPCR array revealed that chondroitin sulfate (CS) biosynthetic enzymes, such as xylosyltransferase 1 (XYLT1) and CHST11, were significantly downregulated during serum-induced GIC differentiation. Simultaneously, the CS modification on CSPG4 was characteristically decreased during the differentiation, and also downregulated by XYLT1 knockdown. Notably, the CS-degradation on CSPG4 by ChondroitinaseABC treatment dramatically induced GIC differentiation, which was significantly inhibited by the addition of CS. GIC growth and differentiation ability were significantly suppressed by CSPG4 knockdown, suggesting that CS-CSPG4 is an important factor in GIC maintenance/differentiation. To understand the molecular function of CS-CSPG4, we analyzed its associating proteins in GICs and found that CSPG4, but not CS-CSPG4, interacts with integrin αV during GIC differentiation. This event sequentially upregulates integrin-ERK signaling, which can be inhibited by cyclic-RGD integrin αV inhibitor. These results indicate that CS-CSPG4 regulates the GIC microenvironment for GIC maintenance/differentiation via the CS moiety which controls integrin signaling. This study demonstrates a novel function of CS on CSPG4 as a niche factor, so-called “glyco-niche” for GICs, and suggests that CS-CSPG4 could be a potential target for malignant glioma.