Abstract 5149: Sialyation of desmosomal protein DSG2: A potential regulator of colorectal cancer cell junctions

Abstract Introduction: Colorectal cancer (CRC) remains one of the most common and deadly cancers in the US. Despite advances in treatment, once CRC is metastatic (spread from the original tumor site to other parts of the body), the 5-year survival rate is 20%. Metastasis requires a complex series of events, including the release of tumor cells from the origin site. Tumor cells adhere to each other via adhesive cell-cell junctions, one family of these is called desmosomes. A key desmosomal protein is Desmoglein-2 (DSG2), which is a cell surface protein. DSG2 function could influence cancer cell detachment and migration, essential steps in metastasis, which has not been fully studied. Upregulation of ST6GAL1, a sialyltransferase that adds sialic acid to proteins in the Golgi, is a hallmark of progression of certain types of cancer. High levels of ST6Gal1 have been linked to worse cancer outcomes. We hypothesized, that increased sialylation of the desmosome protein DSG2 by ST6GAL1 in CRC enhances its surface localization, possibly altering its function. Methods: Human SW620 CRC ST6GAL1 control (CV) and ST6GAL1 knockdown (KD) cells were cultured and utilized to evaluate the presence of DSG2 through three methods: SNA- lectin pull-down assay (SNA recognizes α2, 6-sialylation caused by ST6GAL1), immunofluorescence (IF), and western blotting (WB). The pull-down samples were evaluated for presence of sialylated DSG2 by WB and further analyzed and quantified using densitometry. For IF staining, cells were fixed, permeabilized, and stained with a DSG2 antibody and DAPI to assess differences in location and presence between KD and CV cells. Quantitative image analysis was performed, utilizing 5 high powered fields per experimental group. Further, to assess the relationship between cell density and DSG2 expression, cells were plated at increasing densities and analyzed by both WB and IF techniques. Results: SNA pull-down assay and WB analysis revealed that DSG2 is α2, 6 sialylated by ST6GAL1. ST6GAL1 CV cells had 2.31 times more sialylated DSG2 than ST6GAL1 KD cells. This was corroborated by DSG2 IF staining. We observed an average surface DSG2 to DAPI ratio in KD cells of 0.09 (SEM ± 0.01) and CV cells’ ratio of 0.20 (SEM ± 0.03) (p=. 0.0353, n=3) such that CV cells had 2.7 times more DSG2. Conclusions: Based on these findings, we hypothesize conclude that ST6GAL1 sialylates DSG2 and that this appears to alter its increased sialylation of the desmosome protein, DSG2, in CRC by ST6GAL1 may enhance DSG2's surface localization which likely alters its function. Further study is needed to investigate how this may alter CRC progression and metastasis. Citation Format: Teresa Chiyanne Beamon, Collin Ainslie, Regina Irwin, Jeremie M. Lever, Alexa L. Mattheyses, Karin M. Hardiman. Sialyation of desmosomal protein DSG2: A potential regulator of colorectal cancer cell junctions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5149.