Zic family member 5 promotes RIO kinase 3 expression to enhance pancreatic cancer survival.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies with few effective therapies available. We previously determined the essential role of Zic family member 5 (ZIC5) in the survival of PDAC cells. In this study, we showed that targeting ZIC5 can effectively shrink PDAC tumors treated with gemcitabine in vivo and investigated the molecular mechanisms involved. When tumor-bearing mice were injected intravenously with ZIC5-targeting small interfering RNA, tumor volume was significantly reduced by gemcitabine treatment. RNA-sequencing analysis was used to identify the genes affected by ZIC5 knockdown. Among these, we selected the genes whose mRNA expression levels correlated with that of ZIC5 in pancreatic cancer and those associated with poor prognosis in patients with pancreatic cancer. Further analysis revealed that RIO kinase 3 (RIOK3) promotes PDAC cell survival, whereas ALDH3B1, PTGES, and TUFT1 contribute to gemcitabine resistance in MiaPaca-2 cells. We identified RIOK3 as a direct target gene of ZIC5 using ChIP and luciferase assays. Furthermore, stable expression of RIOK3 in PANC-1 cells reversed the reduction in cell number following ZIC5 knockdown. These findings highlight RIOK3 as a critical target of ZIC5, which is involved in survival signaling in PDAC cells.