Intracellular MUC20 variant 2 maintains mitochondrial calcium homeostasis and enhances drug resistance in signet ring cell carcinoma

Signet ring cell carcinoma (SRCC) is a specific histologic variant in gastric cancer (GC). We analyzed a comprehensive GC cell line database to identify the specifically expressed genes in gastric SRCC. Among the 16 genes highly expressed in SRCC based on the analysis, we focused on MUC20 and investigated its role in gastric SRCC progression. First, the cohort analysis revealed that GC patients with high MUC20 expression exhibited a poor prognosis and that MUC20 expression was significantly correlated with SRCC histological type. Moreover, we found that gastric SRCC cells specifically expressed MUC20 variant 2 (MUC20v2), which was dominantly expressed in the cytoplasm. Silencing MUC20v2 caused cell death with characteristic morphological changes in gastric SRCC cells. To further determine the types of cell death, we assessed apoptosis, pyroptosis and ferroptosis by detecting cleaved PARP, gasdermin E-N-terminal (GSDME-N), and lipid reactive oxygen species (ROS) levels, respectively. We found that apoptosis and pyroptosis occurred in MUC20-silenced gastric SRCC cells. However, MUC20v2-overexpressing non-SRCC cells exhibited chemoresistance to cisplatin (CDDP) and paclitaxel (PTX). In addition, RNA sequencing revealed that pathways involved in intracellular calcium regulation were significantly upregulated in MUC20v2-overexpressing non-SRCC cells. Notably, forced expression of MUC20v2 in the cytoplasm of non-SRCC cells led to the maintenance of mitochondrial calcium homeostasis and mitochondrial membrane potential (MMP), which resulted in cell survival and chemoresistance by suppressing apoptosis and pyroptosis. Finally, we investigated the significance of MUC20v2 in a xenograft model treated with CDDP and showed that MUC20v2 overexpression caused chemoresistance by inhibiting cell death. These findings highlight the novel potential functions of MUC20v2 in conferring cell survival and drug resistance in SRCC cells.