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Cloning of cDNA with possible transcription factor activity at the G1-S phase transition in human fibroblast cell lines.

Normal human fibroblasts have a finite proliferative capacity in vitro. Thus, immortalization of human cells is associated with cellular aging. We have established an immortalization-sensitive cell line from fibroblasts of Wilms' tumor patients which have a partial deletion of chromosome 1 1p. This cell line was easily immortalized by introducing SV4OT. By differential hybridization using both SV4OT-introduced crisis cells and young cells, we cloned a gene that was highly expressed in 1 1p-cells at the time of the crisis and named this gene C-1. Nucleotide sequence analysis of C-1 revealed that it contains a helix-loop-helix domain, indicating that it may be a transcription factor. Expression of the C-1 gene was transiently induced early in the G0-to-S phase transition in two normal human (OUMS-24 and HSF-412) and a non-tumorigenic immortal human (OUMS-24F) fibroblast cell lines, while the other immortal SUSM-1 cells highly expressed the C-1 gene in the middle G1 phase. These results suggest that the C-1 gene product may function as a transcription factor related to the cell cycle.