DNA polymerase POLD1 promotes proliferation and metastasis of bladder cancer by stabilizing MYC

Hitherto, most studies on DNA polymerase δ (POLD1) have mainly focused on the effect of POLD1 inactivation mutation in tumors. Nonetheless, the mechanism underlying high POLD1 expression in tumorigenesis remains elusive. Herein, we substantiated the pro-carcinogenic role of POLD1 in bladder cancer (BLCA) and found that POLD1 expression is related to malignancy and prognosis of BLCA. Next, we demonstrated that POLD1 could promote proliferation and metastasis of BLCA via MYC in vivo and in vitro. Furthermore, POLD1 and MYC were colocalized in the nucleus and co-expressed during the cell cycle. Mechanistically, we validated that POLD1 could interact directly with MYC, and POLD1 could stabilize MYC by counteracting GSK3β-mediated phosphorylation of threonine 58 and blocking the interaction between E3 ubiquitin ligase FBXW7 and MYC. Moreover, MYC could transcriptionally activate POLD1, forming a POLD1-MYC positive feedback loop to enhance the pro-carcinogenic effect of POLD1-MYC on BLCA. Overall, our study identified a novel MYC-driven oncogene POLD1, providing a potential diagnostic and therapeutic target for BLCA. To investigate the downstream mechanism of POLD1 regulation of bladder cancer, we performed RNA sequencing on three repeated siNC and siPOLD1-treated 5637 cells.