Differential role of MEK5alpha and MEK5beta in BMK1/ERK5 activation.
Big mitogen-activated protein kinase 1/extracellular-regulated kinase 5 (BMK1/ERK5) is regulated sequentially by a series of upstream MAP kinase kinases (MEKs) in a signaling cascade. MEKs activate their downstream MAPK by phosphorylation of threonine and tyrosine in the T- X-Y motif. MEK5 is the upstream BMK1 kinase and exists as naturally occurring splice variants, MEK5alpha and MEK5beta. The full-length MEK5 (MEK5alpha) is 89 amino acids longer than MEK5beta at the N terminus, but the precise functional difference between the two splice variants is not known. Dual phosphorylation site mutation of MEK5alpha (Ser-311 --> Asp and Thr- 315 --> Asp; MEK5alpha(S311D/T315D)) activated BMK1, but the corresponding dual phosphorylation sites mutant of MEK5beta could not induce BMK1 kinase activation or nuclear translocation. Furthermore, MEK5beta inhibited epidermal growth factor-induced BMK1 activation and MEK5alpha(S311D/T315D)-induced MEF2 transcriptional activity. Both MEK5alpha and MEK5beta individually co-immunoprecipitated with BMK1, but the presence of MEK5beta prevented association of MEK5alpha with BMK1 suggesting a mechanistic basis for the dominant-negative behavior of MEK5beta on BMK1 activation. The ratio of MEK5alpha to MEK5beta expression was higher in cancer cell lines, and overexpression of MEK5beta-inhibited serum-induced DNA synthesis. These data suggest that alternative splicing of MEK5alpha and MEK5beta may play a critical role in BMK1 activation and subsequent cell proliferation.
Cameron
Scott J
SJ
Department of Pharmacology/Physiology, Center for Cardiovascular Research, Department of Anesthesiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
Abe
Jun-Ichi
J
Malik
Sundeep
S
Che
Wenyi
W
Yang
Jay
J
D021581:Active Transport, Cell Nucleus; D017398:Alternative Splicing; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002455:Cell Division; D002460:Cell Line; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D005799:Genes, Dominant; D049452:Green Fluorescent Proteins; D006801:Humans; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection
D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins