Glucose-regulated protein 94 deficiency induces squamous cell metaplasia and suppresses PTEN-null driven endometrial epithelial tumor development

Endometrial carcinoma is the most prevalent gynecologic cancer in the United States. The tumor suppressor gene Pten (phosphatase and tensin homolog) is commonly mutated in the more common type 1 (endometrioid) subtype. The glucose-regulated protein 94 (GRP94) is emerging as a novel regulator for cancer development. Here we report that expression profiles from the Cancer Genome Atlas (TCGA) showed significantly increased Grp94 mRNA levels in endometrial tumor versus normal tissues, correlating with highly elevated GRP94 protein expression in patient samples and the requirement of GRP94 for maintaining viability of human endometrioid adenocarcinoma (EAC) cell lines. Through generation of uterus-specific knockout mouse models with deletion of Grp94 alone (c94(f/f)) or in combination with Pten (cP(f/f)94(f/f)), we discovered that c94(f/f) uteri induced squamous cell metaplasia (SCM) and reduced active nuclear β-catenin. The cP(f/f)94(f/f) uteri showed accelerated SCM and suppression of PTEN-null driven EAC, with reduced cellular proliferation, attenuated β-catenin signaling and decreased AKT/S6 activation in the SCM. In contrast to single PTEN knockout uteri (cP(f/f)), cP(f/f)94(f/f) uteri showed no decrease in E-cadherin level and no invasive lesion. Collectively, our study implies that GRP94 downregulation induces SCM in EAC and suppresses AKT/S6 signaling, providing a novel mechanism for suppressing EAC progression.