Specific inhibition of NF-Y subunits triggers different cell proliferation defects.

Regulated gene expression is essential for a proper progression through the cell cycle. The transcription factor NF-Y has a fundamental function in transcrip- tional regulation of cell cycle genes, particularly of G2/M genes. In order to investigate common and distinct functions of NF-Y subunits in cell cycle regulation, NF-YA, NF-YB and NF-YC have been silenced by shRNAs in HCT116 cells. NF-YA loss led to a delay in S-phase progression, DNA damage and apoptosis: we showed the activation of the replication checkpoint, through the recruit- ment of "p53 and of the replication proteins PCNA and Mcm7 to chromatin. Differently, NF-YB deple- tion impaired cells from exiting G2/M, but did not interfere with S-phase progression. Gene expres- sion analysis of NF-YA and NF-YB inactivated cells highlighted a common set of hit genes, as well as a plethora of uncommon genes, unveiling a different effect of NF-Y subunits loss on NF-Y binding to its target genes. Chromatin extracts and ChIP analysis showed that NF-YA depletion was more effect- ive than NF-YB in hitting NF-Y recruitment to CCA AT-promoters. Our data suggest a critical role of NF-Y expression, highlighting that the lack of the single subunits are differently perceived by the cells, which activate diverse cell cycle blocks and signaling pathways.