STRUCTURE OF THE GENE ENCODING THE HUMAN CYCLIN-DEPENDENT KINASE INHIBITOR P18 AND MUTATIONAL ANALYSIS IN BREAST-CANCER

The cyclin-dependent kinase (CDK) inhibitor p18 blocks progression of the cell cycle by associating with the cyclin D-dependent kinases CDK6 and CDK4. To better understand the regulation of p18 gene expression, we isolated full-length cDNA clones from a human BT-20 breast cancer cell cDNA library. These clones were then used to isolate the human ge ne from a human genomic DNA library. The human p18 gene spans at least 7.5 kb and is composed of three exons, two of which encode the p18 pr otein. The genomic clone we isolated contained 5 kb of putative promot or sequence which directed expression of the luciferase reporter gene in transient transfection experiments. The longest cDNA that we isolat ed from BT-20 cells contained 2103 nucleotides which corresponds to th e size of the major RNA transcript detected by Northern analysis in th ese cells. Transcription start sites mapping to the 5' end of the puta tive full-length cDNA were identified by ribonuclease protection assay s. A novel polymorphism was identified in the 3' untranslated region o f BT-20 cell cDNA clones that contained the previously described codon 72 mutation. The codon 72 mutation was also detected in 3 of 35 breas t tumors analyzed using a mismatch PCR/RFLP strategy. (C) 1998 Academi c Press.