Possible role of subunit A of nuclear factor Y (NF-YA) in normal human diploid fibroblasts during senescence

NF-Y, a heterotrimeric CCAAT binding protein, may have a role in regulating some Gl/S genes whose expressions are attenuated during replicative senesc ence [Matuoka and Chen (1999) Exp Cell Res 253. 365-371]. The hallmark of r eplicative senescence is the loss of dividing potential. Hence, attenuation of Gl/S gene expressions may be causally related to aging. To understand h ow NF-Y is involved in regulating Gl/S genes during replicative senescence, we have examined the expressions of three NF-Y subunit genes in human IMR- 90 cells over the entire course of their life-span. The mRNA levels of NF-Y A, B, and C did not show any age-dependent change. In contrast, the protein level of NF-YA exhibited a significant and progressive decrease during cel l senescence. Cross-linking experiments indicated that NF-Y may interact wi th proteins such as GCN5 and P/CAF Co-transfection of cells with plasmid en coding NF-YA protein enhanced the expression of reporter gene fused with Gl /S gene promoter that contains NF-Y sites. In contrast, co-transfection wit h plasmid encoding the dominant negative NF-YA mutant suppressed the expres sion of the reporter genes. Transient transfection of human cells with domi nant negative NF-YA mutant could lead to an increase in neutral beta -galac tosidase activity, a marker of cell senescence. These results support the v iew that NF-Y may have a rule in cell senescence.