ZFAT is a conserved regulator of G1/S transition across human cell types

Cell cycle checkpoints are essential for proper cell division and genomic integrity. Here, we identify the nuclear zinc finger protein ZFAT as a novel and essential regulator of the G1/S transition. Using siRNA-mediated knockdown in HT1080 human fibrosarcoma cells, we investigated the consequences of ZFAT depletion on cell cycle progression. Propidium iodide-based DNA content analysis revealed that ZFAT depletion caused G1 accumulation and a reduced proportion of S-phase cells, detectable as early as 24 h post-transfection. Consistently, ZFAT silencing reduced DNA synthesis, as shown by EdU incorporation assays, and decreased the proportion of S-phase cells, as confirmed by cyclin A2 immunofluorescence. Furthermore, using a double-thymidine block to synchronize the cell cycle, we found that ZFAT-depleted cells largely failed to progress from G1 into S phase. Together, these complementary observations directly demonstrate that ZFAT depletion blocks the G1/S transition. Importantly, this phenotype was consistently observed in additional cancer cell lines, HCT116 and HeLa cells, as well as in non-transformed RPE1 cells, indicating that ZFAT-dependent regulation of G1/S transition is broadly conserved across diverse human cell types. Together, these findings establish ZFAT as a conserved and essential regulator of G1/S transition in human cells.