MRK, a mixed lineage kinase-related molecule that plays a role in gamma-radiation-induced cell cycle arrest.
Mitogen-activated protein (MAP) kinase pathways are three-kinase modules that mediate diverse cellular processes and have been highly conserved among eukaryotes. By using a functional complementation screen in yeast, we have identified a human MAP kinase kinase kinase (MAPKKK) that shares homology with members of the mixed lineage kinase (MLK) family and therefore was called MRK (MLK-related kinase). We report the structure of the MRK gene, from which are generated two splice forms of MRK, MRK-alpha and MRK-beta, encoding for proteins of 800 and 456 amino acids, respectively. By using a combination of solid phase protein kinase assays, transient transfections in cells, and analysis of endogenous proteins in stably transfected Madin-Darby canine kidney cells, we found that MRK-beta preferentially activates ERK6/p38gamma via MKK3/MKK6 and JNK through MKK4/MKK7. We also show that expression of wild type MRK increases the cell population in the G(2)/M phase of the cell cycle, whereas dominant negative MRK attenuates the G(2) arrest caused by gamma-radiation. In addition, exposure of cells to gamma-radiation induces MRK activity. These data suggest that MRK may mediate gamma-radiation signaling leading to cell cycle arrest and that MRK activity is necessary for the cell cycle checkpoint regulation in cells.
Gross
Eleanore A
EA
Picower Institute for Medical Research, Manhasset, New York 11030, USA.
Callow
Marinella G
MG
Waldbaum
Linda
L
Thomas
Suzanne
S
Ruggieri
Rosamaria
R
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D019556:COS Cells; D002453:Cell Cycle / Q000528:radiation effects*; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004285:Dogs; D005720:Gamma Rays; D015723:Gene Library; D005799:Genes, Dominant; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D048291:Mitogen-Activated Protein Kinase 12; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014018:Tissue Distribution; D015533:Transcriptional Activation; D014162:Transfection
D018076:DNA, Complementary; C097276:CILK1 protein, human; D048291:Mitogen-Activated Protein Kinase 12; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases