RINT1 downregulation disrupts pancreatic ductal adenocarcinoma homeostasis

Despite intensive basic and translational research, pancreatic ductal adenocarcinoma (PDAC) has still a dismal prognosis. Therefore, understanding cellular homeostasis more in detail and identifying potential druggable targets is crucial to improve patient outcome. RINT1 (RAD50-interacting protein 1) facilitates cell cycle progression, genomic stability, telomere maintenance, and ER-Golgi trafficking. Rare RINT1 missense mutation and RINT1 overexpression were shown to predispose to tumor development including colorectal cancer and Lynch-syndrome type cancers. Therefore, we aimed to investigate the role of RINT1 in human PDAC by database analysis, relevance of RINT1 expression on patient survival suffering from PDAC and shRNA mediated knockdown of RINT1 in human PDAC cell lines. Of all investigated human PDAC patients, database analysis revealed a copy number alteration in 37 % and a mutation frequency of RINT1 in 1.75 %, respectively. Additionally, we revealed that protein expression level of RINT1 directly correlated with survival of patients suffering from PDAC. Strong RINT1 expression (score 5) was associated with shortest survival, whereas patients with low levels (score 1) had the best survival. Interestingly, tumor negative for RINT1 expression (score 0) showed a significant increase in poorly differentiated tumors (Grade ≥ 3) compared to RINT1 positive tumors. To characterize cellular function of RINT1, we found that shRNA-mediated RINT1 depletion in human PDAC cell lines led to severe growth defects in vitro associated with G2 cell cycle arrest caused by increased DNA-Damage. In addition, we demonstrated that RINT1 knockdown disrupted Golgi-ER-homeostasis. The overall cellular defects triggered the activation of cell death by apoptosis and partly necroptosis. In subcutaneous and orthotopic xenografts, RINT1 deletion clearly controlled tumor progression. We identified strong immune cell infiltration in athymic nude mice in RINT1-deficient tumors. However, these immune cells do not directly control tumor progression, nevertheless suggesting a potential re-activation of the host immune response in vivo. Our data clearly point out that RINT1 is essential for PDAC survival and represents therefore a putative therapeutic target.

Publikationsverlauf

Artikel online veröffentlicht:
08. September 2020