FUNCTIONAL-ANALYSIS OF THE HUMAN CYCLIN D2 AND CYCLIN D3 PROMOTERS

The D-type cyclins promote progression through the G(1) phase of the c ell cycle and may provide a link between growth factors and the cell c ycle machinery. We determined the nucleotide sequence of the 5'-flanki ng region of the human cyclin D2 and cyclin D3 genes and identified th e transcription start sites. Analysis of the upstream sequences requir ed for transcription of the cyclin D2 and cyclin D3 genes in continuou sly dividing cells revealed marked differences in their regulatory ele ments. In the cyclin D2 gene positive elements were localized between positions -306 and -114 relative to the ATG codon at +1. Additional po sitive elements were localized between -444 and -345, whereas sequence s that reduced transcription were identified between nucleotides -1624 and -892. In the cyclin D3 gene all of the positive elements required for maximal transcription were localized between nucleotides -366 and -167, and no negative elements were found. The activities of a report er gene linked to the upstream regulatory sequences of the cyclin D2 g ene but not the cyclin D3 gene were induced when starved cells were se rum stimulated. This suggests that although the abundance of both the cyclin D2 and cyclin D3 mRNAs is increased by serum stimulation, only the cyclin D2 gene is up-regulated at the transcriptional level. Seque nces between nucleotides -306 and -1624 of the cyclin D2 gene were nec essary for serum inducibility.