RB1CC1 suppresses cell cycle progression through RB1 expression in human neoplastic cells.

RB1-inducible Coiled-Coil 1 (RB1CC1) is a putative transcription factor that functions as a key regulator of retinoblastoma 1 (RB1). RB1CC1 mutations lacking this function are involved in the tumorigenesis of breast cancers. RB1CC1 is distributed in various tissues other than the breast, and is thought to play a biological role in controlling cell growth and progression of various cancers. The present study examined the correlation between RB1CC1 and cell cycle-related molecules in human neoplastic cells, and the ratios of cells at various phases of the cell cycle were verified in the RB1CC1-transduced human leukemic cell lines, K562 and Jurkat. The results showed that RB1CC1 was synchronously expressed with RB1 in various cell lines and that introducing RB1CC1 induced RB1 expression in human leukemic cell lines, although independently of the other molecules. Western blotting showed that underphosphorylated forms of RB1 were elicited by RB1CC1, whereas E2F1 was not affected. Cell cycle analysis demonstrated that G2-M phases were suppressed in RB1CC1-transduced cells. These data suggested that RB1CC1 induces the expression of RB1, especially of underphosphorylated forms, then suppresses cell cycle progression in human neoplastic cells.