Abstract 3956: Dystroglycan receptor and FER maintain melanoma dormancy in the vascular niche

Cancer recurrence after therapy and long periods of remission are frequent in melanoma patients, likely due to the presence of residual disseminated tumor cells (DTCs). DTCs can enter dormancy and become refractory to targeted or conventional therapies. Extracellular matrix (ECM) proteins and basement membrane (BM) formation are critical structural components required to support the tumor microenvironment. Dystroglycan (DG) receptor complex, which is highly glycosylated in the alpha subunit, is a crucial ECM binding receptor because it functions in bridging the ECM and the cytoskeleton. DG receptor has been implicated in a variety of cancers, including melanoma, but its function in DTCs and dormancy has not been evaluated. In this study, we performed a bioinformatics analysis to study the implication of mutations in DAG1 (DG receptor gene) and its associated genes in cutaneous melanoma patients. We found that patients harboring mutations in the protein O-mannosyltransferase 1 enzyme (POMT1), which is essential for the transfer of a mannosyl residue to the alpha-DG subunit, had a significantly lower median months survival (27 months) compared to those with no POMT1 mutations (61 months). We noted missense mutations (Phe-Ser) in DAG1 occurred in the mucin-like region of the alpha subunit of DG. Also, the expression of DAG1, dystrophin (DMD), and utrophin (UTRN) at the mRNA level was significantly augmented under the presence of DAG1 mutations compared to the cohort of patients without DAG1 mutations. We evaluated the expression of alpha-DG, dystrophin, utrophin, and non-receptor tyrosine kinase (FER) to establish a potential relationship between the DAG receptor complex and FER in a metastatic mouse model. This mouse model is based on the overexpression of GPCRs (Tg(Grm1)Epv(E)/K5-tTA-Edn3) and spontaneously develops melanoma tumors on the ear, tail and dorsal skin, and presents with 90% penetrance of metastasis in the lymph nodes and lung. Using a genetic lineage tracing, we detected the presence of intravascular metastatic cells in the lung that are negative for Ki67 (proliferation marker), caspase3 (apoptosis marker), and other dormancy markers (p21, p27, p-ERK) indicating they are in a dormant state. The intravascular dormant DTC cells expressed high levels of alpha-DG and utrophin, and moderate levels of dystrophin but low levels of FER. Overall, our results suggest that alterations in alpha-DG glycosylation resulting from POMT1 mutations and subsequent