E2F1-Mediated Upregulation of p19INK4d Determines Its Periodic Expression during Cell Cycle and Regulates Cellular Proliferation

ABEL C. CARCAGNO; MARIELA C. MARAZITA; MARÍA F. OGARA; JULIETA M. CERUTI; SILVIAN V. SONZOGNI; MARÍA E. SCASSA; LUCIANA E. GIONO; CANEPA, EDUARDO TOMAS

PLOS ONE

PUBLIC LIBRARY SCIENCE

Año: 2011 vol. 6 p. 1 - 13

1932-6203

Background: A central aspect of development and disease is the control of cell proliferation through regulation of themitotic cycle. Cell cycle progression and directionality requires an appropriate balance of positive and negative regulatorswhose expression must fluctuate in a coordinated manner. p19INK4d, a member of the INK4 family of CDK inhibitors, has aunique feature that distinguishes it from the remaining INK4 and makes it a likely candidate for contributing to thedirectionality of the cell cycle. p19INK4d mRNA and protein levels accumulate periodically during the cell cycle undernormal conditions, a feature reminiscent of cyclins.Methodology/Principal Findings: In this paper, we demonstrate that p19INK4d is transcriptionally regulated by E2F1through two response elements present in the p19INK4d promoter. Ablation of this regulation reduced p19 levels andrestricted its expression during the cell cycle, reflecting the contribution of a transcriptional effect of E2F1 on p19periodicity. The induction of p19INK4d is delayed during the cell cycle compared to that of cyclin E, temporally separatingthe induction of these proliferative and antiproliferative target genes. Specific inhibition of the E2F1-p19INK4d pathwayusing triplex-forming oligonucleotides that block E2F1 binding on p19 promoter, stimulated cell proliferation and increasedthe fraction of cells in S phase.Conclusions/Significance: The results described here support a model of normal cell cycle progression in which, followingphosphorylation of pRb, free E2F induces cyclin E, among other target genes. Once cyclinE/CDK2 takes over as the cell cycledriving kinase activity, the induction of p19 mediated by E2F1 leads to inhibition of the CDK4,6-containing complexes,bringing the G1 phase to an end. This regulatory mechanism constitutes a new negative feedback loop that terminates theG1 phase proliferative signal, contributing to the proper coordination of the cell cycle and provides an additionalmechanism to limit E2F activity.