DEREGULATION OF CDC2 GENE-EXPRESSION CORRELATES WITH OVEREXPRESSION OF A 110 KDA CCAAT BOX-BINDING FACTOR IN TRANSFORMED-CELLS

Eukaryotic cell cycle progression is regulated by an orderly and seque ntial activation of several cyclin-dependent kinases, which phosphoryl ate key substrates during this process. p34(cdc2), the catalytic subun it of cdc2 kinase, is expressed at the late G(1)/S boundary and is req uired for the G(2)-->M phase transition. Transactivation of the human cdc2 promoter by the DNA tumor virus-encoded oncogenic protein SV40 la rge T antigen is mediated by induction of a novel 110 kDa CCAAT box bi nding factor (CBF/cdc2), To investigate whether induction of CBF/cdc2 is an intrinsic property of the viral oncoprotein or is a common event during transformation of normal cells, expression of CBF/cdc2 was ana lyzed in many human tumor cell lines and in rodent cells spontaneously transformed or stably expressing various oncogenes, Our results showe d that CBF/cdc2 was overexpressed in all transformed cells examined, i ncluding human 293, MCF-7, HeLa and HepG2 cells. Moreover, expression of CBF/cdc2 was elevated in spontaneously transformed rat liver epithe lial cells (C4T), but not detectable in the non-tumorigenic parental ( RLE) cells. The elevated levels of CBF/cdc2 expression in C4T cells co rrelated well with increased cdc2 mRNA and p34(cdc2) levels. CBF/cdc2 was also overexpressed in a rat liver epithelial cell line (WB) stably transfected with various oncogenes, v-myc, v-Ha-ras and mutated rat n eu and v-src, Using an electrophoretic mobility shift assay, specific binding of CBF/cdc2 to the CCAAT box motifs of the human cdc2, cycA an d cdc25C promoters was detected, suggesting that transcription of thes e cell cycle regulatory genes are coordinately activated by CBF/cdc2.