The Cyclin-dependent Kinase Inhibitor p16INK4a Physically Interacts with Transcription Factor Sp1 and Cyclin-dependent Kinase 4 to Transactivate MicroRNA-141 and MicroRNA-146b-5p Spontaneously and in Response to Ultraviolet Light-induced DNA Damage

p16INK4a is a tumor suppressor protein involved in several stress-related cellular responses, including apoptosis. Recent lines of evidence indicate that p16INK4a is also a modulator of gene expression. However, the molecular mechanisms underlying this novel function are still obscure. Here, we present clear evidence that p16INK4a modulates the levels of various microRNAs, with marked positive effect on miR-141 and miR-146b-5p. This effect is mediated through the formation of the p16-CDK4-Sp1 heterocomplex, which binds to Sp1 consensus-binding motifs present in the promoters of miR-141 and miR-146b-5p, and it enables their transcription. In addition, we have shown that p16INK4a interacts with Sp1 through the fourth ankyrin repeat, which is crucial for Sp1 binding to the miR-141 and miR-146b-5p promoters and their transcriptional activation. The physiological importance of this association was revealed by the inability of cancer-related p16INK4a mutants to interact with Sp1. Moreover, we have shown p16-CDK4-Sp1-dependent up-regulation of miR-141 and miR-146b-5p following UV light-induced DNA damage and the role of these two microRNAs in mediating p16-related induction of apoptosis in response to this genotoxic stress. Together, these results indicate that p16INK4a associates with CDK4 not only to inhibit the cell cycle but also to enable the transcription of two important onco-microRNAs, which act as downstream effectors. Background: The cyclin-dependent kinase inhibitor p16INK4a is also a modulator of gene expression through an unknown mechanism. Results: p16INK4a-CDK4 forms a heterocomplex with Sp1, which induces the expression and UV-dependent up-regulation of miR-141 and miR-146b-5p. Conclusion: p16INK4a-CDK4 complex has transcriptional activity through interaction with the transcription factor Sp1. Significance: The microRNAs are novel effectors of the p16INK4a-CDK4 complex.