A U-Rich Element in the 5′ Untranslated Region Is Necessary for the Translation of p27 mRNA

Abstract

Increased translation of p27 mRNA correlates with withdrawal of cells from the cell cycle. This raised the possibility that antimitogenic signals might mediate their effects on p27 expression by altering complexes that formed on p27 mRNA, regulating its translation. In this report, we identify a U-rich sequence in the 5′ untranslated region (5′UTR) of p27 mRNA that is necessary for efficient translation in proliferating and nonproliferating cells. We show that a number of factors bind to the 5′UTR in vitro in a manner dependent on the U-rich element, and their availability in the cytosol is controlled in a growth- and cell cycle-dependent fashion. One of these factors is HuR, a protein previously implicated in mRNA stability, transport, and translation. Another is hnRNP C1 and C2, proteins implicated in mRNA processing and the translation of a specific subset of mRNAs expressed in differentiated cells. In lovastatin-treated MDA468 cells, the mobility of the associated hnRNP C1 and C2 proteins changed, and this correlated with increased p27 expression. Together, these data suggest that the U-rich dependent RNP complex on the 5′UTR may regulate the translation of p27 mRNA and may be a target of antimitogenic signals.

ACKNOWLEDGMENTS

We thank James Roberts (FHCRC, Seattle, Wash.), Ken Marians (MSKCC), and Gino Vairo (AMRAD, Australia) and members of the laboratory for discussions during completion of these studies and comments on the manuscript. We thank Henry Furneaux (MSKCC) and Myriam Gorospe (National Institute of Aging, NIH) for sharing unpublished data and results with HuR reduction experiments. We thank Serafin Pinol-Roma (Mt. Sinai, New York, N.Y.), Stacy Blain (MSKCC), and Merck for their generosity with the 4F4 hnRNP C1/C2 antibody, the p27ck− construct, and lovastatin, respectively. We thank Paul Tempst (MSKCC) and the protein sequencing facility for mass fingerprinting p40/41.

This work was supported by funds from the National Institutes of Health (GM52597, A.K.) and the National Cancer Institute (Cancer Center grant CA08748 to Memorial Sloan-Kettering Cancer Center). A.V. is supported by an FPI fellowship of the Spanish Ministry for Education and Culture. A.K. is a Pew Scholar in Biomedical Sciences, an Irma T. Hirschl Scholar, and the incumbent of the Frederick R. Adler Chair for Junior Faculty at Memorial Sloan-Kettering Cancer Center.