Abstract
BACKGROUND: An imbalance between the expression of cell cycle-promoting and cell cycle-inhibiting genes triggers uncontrolled cell cycle progression in cancer cells. However, the mechanism controlling the expression of cell cycle-related genes, especially those whose expression is mediated by RNA-binding proteins (RBPs), remains elusive. METHODS: All RBP expression in human breast cancer was analyzed by bioinformatic methods. The expression and prognostic value of RBPs ZC3H12D (zinc finger CCCH domain-containing protein 12D) and DDX5 (DEAD box protein 5) in breast cancer were analyzed in public databases and tumor samples. The functions of ZC3H12D and DDX5 in breast tumor cell cycle regulation and tumor progression were determined in vitro and in vivo. RNA sequencing, infrared crosslinking immunoprecipitation and RNA sequencing (irCLIP-Seq), RNA immunoprecipitation (RIP), luciferase assay, mRNA stability detection, protein pull-down, RNA pull-down, mass spectrometry, immunocytochemistry, RNA-EMSA, and RNA immunoprecipitation chromatin immunoprecipitation (RIP-ChIP) were conducted to determine the underlying molecular mechanisms of ZC3H12D and DDX5. RESULTS: The expression of ZC3H12D and DDX5 was reduced and increased in human breast cancer tissues, respectively, and was closely related to the prognosis of breast cancer patients. ZC3H12D and DDX5 could inhibit or promote breast tumor progression by reciprocally controlling the G1/S transition of tumor cells. Mechanistically, ZC3H12D destabilized the CCND1 mRNA by directly binding the conserved stem-loop structure localized in the 3'-untranslated region (3'UTR) via the RNase domain. Ribosomal protein L4 (RPL4) was critical for ZC3H12D-mediated mRNA degradation. Besides, DDX5 was shown to bind the common RNA stem-loop structure of CCND1 but increased its stability. CONCLUSIONS: ZC3H12D and DDX5 are a pair of cell cycle antagonists in breast cancer that inhibit or promote the cell cycle progression by modulating the expression of cell cycle-promoting genes, which provide new insights into the prevention of uncontrolled cancer cell cycle transitions.