Regulation of peripheral node addressin in tumor-associated CD31+ vascular endothelial cells.

Abstract

Abstract Naïve T cells use peripheral node addressin (PNAd), normally found on lymph node (LN) high endothelial venules (HEV), to traffic into lymphoid organs. We previously reported that the vasculature of murine tumors expressed PNAd and CCL21, which supports infiltration and intratumoral activation of naïve T cells, in turn delaying tumor growth. PNAd expression on tumor vasculature depends on effector CD8+ T cells that secrete LTα3, which signals through TNFR on tumor-associated CD31+ endothelial cells. PNAd expression is low on tumor vasculature, suggesting that it might be regulated differently than PNAd on HEV. Using RT-qPCR, we found that most of the enzymes responsible for PNAd synthesis are expressed comparably in CD31+ cells from tumors and LN. However, the primary sulfotransferase responsible for the generation of the 6-sulfo sialyl Lewis X structure on PNAd HEV, GlcNAc6ST-2, is minimally expressed in tumors. Tumor CD31+ cells expressed equivalent levels of GlcNAc6ST-1, suggesting that it is responsible for low-level PNAd expression. Of the scaffolding proteins that make up PNAd, GlyCAM-1 was minimally expressed in tumor CD31+ cells, whereas all others were expressed comparably. To identify the components of PNAd biosynthesis in tumor CD31+ cells that are controlled by LTα3-TNFR signaling, we evaluated tumors from WT and TNFR1/2KO mice. GlyCAM-1 was the only assessed PNAd component that was ablated in TNFR1/2KO tumors. However, based on transcript levels, GlyCAM-1 accounts for only about 10% of the PNAd scaffolding proteins in tumor CD31+ cells. This suggests that TNFR signaling regulates additional PNAd biosynthetic components yet to be examined, or that it regulates one or more components at the level of protein translation.