title: CHK down-regulates SCF/KL-activated Lyn kinase activity in Mo7e megakaryocytic cells.
abstract: The Csk Homologous Kinase (CHK) has been shown to have an enzymatic activity similar to the tyrosine kinase Csk in that it down-regulates Src family kinase activity by causing phosphorylation of the Src C-terminal tyrosine residue. In megakaryocytic Mo7e cells, CHK associates with a specific phosphotyrosine juxtamembrane sequence of the SCF/KL-activated c-Kit receptor. Here, we show that in Mo7e cells, the major Src family kinase activity is p53/56(Lyn). Studies using immobilized c-Kit phosphopeptides show that Lyn is able to specifically associate with the tyrosine-phosphorylated juxtamembrane 568Y*VY*IDPT sequence of c-Kit which has previously been shown to associate with CHK. In cells over-expressing CHK by means of a recombinant vaccinia virus, we observed an elimination of the SCF/KL-stimulated Lyn kinase peak of activity observed at 2-5 minutes in cells infected with the helper T7-expressing vaccinia virus by itself. Examination of total tyrosine phosphorylation by Western blotting showed that over-expression of CHK resulted in a reduction in the levels of tyrosine phosphorylations in the range of 50-60 kDa, but had no apparent effect on c-Kit autophosphorylation. Taken together, these findings show that CHK is able to down-regulate SCF/KL-stimulated Lyn activity in megakaryocytes.
authors.affiliation: Divisions of Experimental Medicine and Hematology/Oncology, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, 4 Blackfan Circle, Boston, Massachusetts, 02115, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Price
authors.forename: B
authors.initials: B
authors.lastname: Rivnay
authors.forename: H
authors.initials: H
authors.lastname: Avraham
mesh_terms: D002460:Cell Line; D015536:Down-Regulation; D008533:Megakaryocytes / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D016392:Proto-Oncogene Proteins pp60(c-src); D013997:Time Factors; D014616:Vaccinia virus / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D011505:Protein-Tyrosine Kinases; C085377:MATK protein, human; D016392:Proto-Oncogene Proteins pp60(c-src); C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases