Parallel and Independent Regulation of Interleukin-3 mRNA Turnover by Phosphatidylinositol 3-Kinase and p38 Mitogen-Activated Protein Kinase

Abstract

AU-rich elements (ARE) present in the 3′ untranslated regions of many cytokines and immediate-early genes are responsible for targeting the transcripts for rapid decay. We present evidence from cotransfection experiments in NIH 3T3 cells that two signaling pathways, one involving phosphatidylinositol 3-kinase (PI3-K), and one involving the p38 mitogen-activated protein kinase (MAPK), lead to stabilization of interleukin-3 mRNA in parallel. Stabilization mediated by either of the two pathways was antagonized by tristetraprolin (TTP), an AU-binding protein known to promote constitutive decay of ARE-containing transcripts. Remarkably, the stabilizing AU-binding protein HuR, in collaboration with p38 MAPK but not with PI3-K, could overcome the destabilizing effect of TTP. These data argue that the stabilizing kinases PI3-K and p38 MAPK do not act through direct inactivation of TTP but via activating pathway-specific stabilizing AU-binding proteins. Our data suggest an integrated model of mRNA turnover control, where stabilizing (HuR) and destabilizing (TTP) AU-binding proteins compete and where the former are under the positive control of independent phosphokinase signaling pathways.

ACKNOWLEDGMENTS

We thank L. Brennan and A. Wyss for their comments on the manuscript, A.-B. Shyu for the NIH 3T3 B2A2 cell line and pTet-myc-over-HuR plasmid, D. A. Cantrell for the rCD2-p110 plasmid, and K. R. Chien for the pcDNA-MKK7D plasmid. We also thank S. Degen for constructing the TTP mutant, B. Gross for performing FACS analysis, and M. Colombi for valuable help in preparing the figures.

This work was supported by grant 31-40816.94 of the Schweizerische Nationalfonds to C.M.