The Ink4a/Arf locus encodes two structurally unrelated tumor suppressor proteins, p16INK4a and p14ARF (murine p19ARF). Invariant inactivation of either the p16INK4a-cyclin D/CDK-pRb pathway and/or p53-p14ARF pathway occurs in most human tumors. Cyclin D1 is frequently overexpressed in breast cancer cells contributing an alternate mechanism inactivating the p16INK4a/pRb pathway. Targeted overexpression of cyclin D1 to the mammary gland is sufficient for tumorigenesis, and cyclin D1−/− mice are resistant to Ras-induced mammary tumors. Recent studies suggest cyclin D1 and p16INK4a expression are reciprocal in human breast cancers. Herein, reciprocal regulation of cyclin D1 and p16INK4a was observed in tissues of mice mutant for the Ink4a/Arf locus. p16INK4a and p19ARF inhibited DNA synthesis in MCF7 cells. p16INK4a repressed cyclin D1 expression and transcription. Repression of cyclin D1 by p16INK4a occurred independently of the p16INK4a-cdk4-binding function and required a cAMP-response element/activating transcription factor-2-binding site. p19ARF repressed cyclin D1 through a novel distal cis-element at −1137, which bound p53 in chromatin-immunoprecipitation assays. Transcriptional repression of the cyclin D1 gene through distinct DNA sequences may contribute to the tumor suppressor function of the Ink4a/Arf locus.
Grant support: This work was supported in part by awards from the Susan Komen Breast Cancer Foundation, Breast Cancer Alliance Inc., Grants R01CA70896, R01CA75503, R01CA86072, R01CA86071 (to R. G. Pestell), and R03AG20337 (to C. Albanese). R. G. Pestell was a recipient of the Irma T. Hirschl and Weil Caulier award and was the Diane Belfer Faculty Scholar in Cancer Research. M. D’Amico was a recipient of the New York State mentored EMPIRE award. Work conducted at the Lombardi Cancer Center was supported by the NIH Cancer Center Core grant. Ink4a/Arf knockout mice were a generous gift from Dr. R. DePinho.
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- Received August 13, 2003.
- Revision received March 30, 2004.
- Accepted April 29, 2004.
- ©2004 American Association for Cancer Research.