Department of Gastroenterological Surgery, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto, 860-8556, Japan.
Gastrointestinal Cancer Biology, International Research Center of Medical Sciences (IRCMS), Kumamoto University, Kumamoto, Japan.
Gastric Cancer. 2022 May;25(3):542-557. doi: 10.1007/s10120-022-01283-z. Epub 2022 Feb 15.
Signet ring cell carcinoma (SRCC) is a particular histologic variant of gastric cancer (GC). However, the critical factor related to the aggressive characteristics of SRCC has not been determined.
We collected surgically resected tissues from 360 GC patients in the Kumamoto University cohort and generated survival curves via the Kaplan-Meier method. In vitro, we identified the specific transcript variant of MUC20 in SRCC cells by direct sequencing and investigated the role of MUC20 in GC progression using GC cells with MUC20 silencing and forced expression. In vivo, we examined chemoresistance using MUC20 variant 2 (MUC20v2)-overexpressing non-SRCC cells to construct a xenograft mouse model.
We analyzed a comprehensive GC cell line database to identify the specifically expressed genes in gastric SRCC. We focused on MUC20 and investigated its role in GC progression. Survival 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 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 examined 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. In addition, MUC20v2-overexpressing GC cells exhibited chemoresistance to cisplatin (CDDP) and paclitaxel (PTX). RNA sequencing revealed that the pathways involved in intracellular calcium regulation were significantly upregulated in MUC20v2-overexpressing GC cells. Notably, forced expression of MUC20v2 in the cytoplasm of GC cells led to the maintenance of mitochondrial calcium homeostasis and mitochondrial membrane potential (MMP), which promoted 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 functions of MUC20v2, which may confer cell survival and drug resistance in GC cells.
MUC20v2 protects GC cells from apoptosis and pyroptosis by maintaining mitochondrial calcium levels and mitochondrial membrane potential and subsequently induces drug resistance.
印戒细胞癌（SRCC）是胃癌（GC）的一种特殊组织学亚型。然而，与 SRCC 侵袭性特征相关的关键因素尚未确定。
我们从熊本大学队列中收集了 360 名 GC 患者的手术切除组织，并通过 Kaplan-Meier 方法生成了生存曲线。在体外，我们通过直接测序鉴定了 SRCC 细胞中 MUC20 的特定转录变体，并通过沉默 GC 细胞中的 MUC20 和强制表达来研究 MUC20 在 GC 进展中的作用。在体内，我们使用过表达 MUC20 变体 2（MUC20v2）的非 SRCC 细胞构建异种移植小鼠模型来检测化疗耐药性。
我们分析了一个全面的 GC 细胞系数据库，以鉴定在胃 SRCC 中特异性表达的基因。我们专注于 MUC20 并研究了其在 GC 进展中的作用。生存分析显示，高 MUC20 表达的 GC 患者预后不良，MUC20 表达与 SRCC 组织学类型显著相关。此外，我们发现胃 SRCC 细胞特异性表达 MUC20v2，其在细胞质中占主导地位。沉默 MUC20v2 导致胃 SRCC 细胞死亡，并伴有特征性的形态学变化。为了进一步确定细胞死亡的类型，我们通过检测裂解的 PARP、gasdermin E-N 末端（GSDME-N）和脂质活性氧（ROS）水平，分别检测了凋亡、焦亡和铁死亡。我们发现凋亡和焦亡发生在沉默 MUC20 的胃 SRCC 细胞中。此外，过表达 MUC20v2 的 GC 细胞对顺铂（CDDP）和紫杉醇（PTX）表现出化疗耐药性。RNA 测序显示，过表达 MUC20v2 的 GC 细胞中线粒体钙调节相关途径显著上调。值得注意的是，MUC20v2 在 GC 细胞质中的强制表达导致线粒体钙稳态和线粒体膜电位（MMP）的维持，从而通过抑制凋亡和焦亡促进细胞存活和化疗耐药性。最后，我们在顺铂处理的异种移植模型中研究了 MUC20v2 的意义，并表明 MUC20v2 通过抑制细胞死亡引起化疗耐药性。
这些发现强调了 MUC20v2 的新功能，它可能赋予 GC 细胞存活和药物耐药性。
MUC20v2 通过维持线粒体钙水平和线粒体膜电位来保护 GC 细胞免于凋亡和焦亡，随后诱导药物耐药性。
