Abstract 4699: Decline in Arylsulfatase B (ARSB) increases PD-L1 expression in melanoma, hepatic, prostate, and mononuclear cells

Abstract

Abstract Arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase) is the enzyme that removes 4-sulfate groups from chondroitin 4-sulfate (C4S) and dermatan sulfate. In previous work, we have shown decline in ARSB with increasing aggressiveness of melanoma cell lines and in association with more aggressive prostate cancers. As ARSB decreases, chondroitin 4-sulfate increases, leading to increased binding of SHP2 (PTP11; non-receptor tyrosine phosphatase) and reduced binding of galectin-3. Subsequent effects include increase in phospho-ERK1/2 and transcriptional effects, including hypermethylation of the DKK3 promoter and reduced expression of DKK (Dickkopf WNT pathway signaling inhibitor) 3, leading to activation of Wnt signaling. Other transcriptional events following silencing of ARSB include: increased expression of CSPG4 and MMP-2 in melanoma cells; increased expression of versican in prostate epithelial cells; increased expression of Wnt9A in colonic epithelial cells; and increased MITF-mediated expression of GPNMB in hepatic cells. Invasiveness of cultured melanoma cells increased when ARSB was silenced by siRNA. To further address the role of ARSB, metastatic melanoma tissue was obtained from the biorepository of the University of Illinois at Chicago. Expression of CSPG4 and MMP2 was increased in the metastatic tissues and SHP2 activity was reduced. When ARSB was silenced by siRNA in cultured normal melanocytes (PCS 200-013, ATCC), Programmed Death-Ligand (PD-L)1 increased from 78 ± 7 pg/mg protein to 128 ± 11 pg/mg protein (ELISA assay; p<0.001). In metastatic melanoma cells (1205 Lu), PD-L1 increased from baseline value of 407 ± 34 pg/mg to 462 ± 26 pg/mg when ARSB was silenced. ARSB activity and expression were reduced in the skin metastases, attributable to increased ARSB promoter methylation. In the skin metastases, PD-L1 increased from 103 ± 2.4 pg/mg protein to 457 ± 49 pg/ml protein. In malignant HepG2 cells, when ARSB was silenced, PD-L1 mRNA expression increased to 1.6 times baseline. In human prostate cell lines, including metastatic PC-3 cells, normal prostate epithelial cells and normal prostate stromal cells, PD-L1 mRNA expression increased to 1.8 times, 2.2 times, and 1.6 times the baseline level when ARSB was silenced. In mononuclear cells of prediabetes participants in a dietary study of carrageenan withdrawal, PD-L1 expression declined by 62% in participants on the no-carrageenan diet over a 12-week period, as ARSB activity increased by 34%. These findings indicate that changes in ARSB contribute to the expression of PD-L1 in human cells and can thereby affect the immune checkpoint response. Further studies are required to determine how decline in ARSB and the resulting increase in N-acetylgalactosamine-4-sulfation lead to increased PD-L1 expression and how treatment with recombinant ARSB might affect the immune responses. Citation Format: Joanne Kramer Tobacman, Sumit Bhattacharyya, Leo Feferman. Decline in Arylsulfatase B (ARSB) increases PD-L1 expression in melanoma, hepatic, prostate, and mononuclear cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4699.