Transcriptional Regulation of Tissue-Specific Genes by the ERK5 Mitogen-Activated Protein Kinase

Abstract

The ERK5 mitogen-activated protein kinase (MAPK) differs from other MAPKs in possessing a potent transcriptional activation domain. ERK5^−/− embryos die from angiogenic defects, but the precise physiological role of ERK5 remains poorly understood. To elucidate molecular functions of ERK5 in the development of vasculature and other tissues, we performed gene profile analyses of erk5^−/− mouse embryos and erk5^−/− fibroblast cells reconstituted with ERK5 or ERK5(1-740), which lacks the transactivation domain. These experiments revealed several potential ERK5 target genes, including a proapoptotic gene bnip3, known angiogenic genes flt1 and lklf (lung Krüppel-like factor), and genes that regulate cardiovascular development. Among these, LKLF, known for its roles in angiogenesis, T-cell quiescence, and survival, was found to be absolutely dependent on ERK5 for expression in endothelial and T cells. We show that ERK5 drives lklf transcription by activating MEF2 transcription factors. Expression of erk5 short hairpin or a dominant-negative form of the ERK5 upstream activator, MEK5, in T cells led to downregulation of LKLF, increased cell size and upregulation of activation markers. Thus, through its kinase and transcriptional activation domains, ERK5 regulates transcriptional responses of cell survival and quiescence critical for angiogenesis and T-cell function.

ACKNOWLEDGMENTS

We thank Herbert Kasler for cloning the MSCV-ERK5 and MSCV-ERK5(1-740) constructs, Martin Guerbadot for technical assistance, and Laurel Lenz for reading the manuscript. We are indebted to the following investigators for their generous gifts: Richard Bruick (University of Texas Southwestern) for the bnip3 reporter (Nip3 prom-pGL3 Basic), José Alberola-Ila for retroviral constructs, and Roger Davis (HHMI, University of Massachusetts) for pCDNA3-Flag-MKK6, pCDNA3-Flag-MKK6(glu), and pCMV-Flag-p38 plasmids. We also thank Michael Cooke (Genomics Institute of the Novartis Research Foundation) for the erk5 shRNA sequences and Jamie Geier and Na Xiong for technical advice on the ChIP assays.