title: The tyrosine kinase CSK associates with FLT3 and c-Kit receptors and regulates downstream signaling.
abstract: Type III receptor tyrosine kinases (RTKs), FLT3 and c-Kit play important roles in a variety of cellular processes. A number of SH2-domain containing proteins interact with FLT3 and c-Kit and regulate downstream signaling. The SH2-domain containing non-receptor protein tyrosine kinase CSK is mainly studied in the context of regulating Src family kinases. Here we present an additional role of this kinase in RTK signaling. We show that CSK interacts with FLT3 and c-Kit in a phosphorylation dependent manner. This interaction is facilitated through the SH2-domain of CSK. Under basal conditions CSK is mainly localized throughout the cytosolic compartment but upon ligand stimulation it is recruited to the inner side of cell membrane. CSK association did not alter receptor ubiquitination or phosphorylation but disrupted downstream signaling. Selective depletion of CSK using siRNA, or inhibition with CSK inhibitor, led to increased phosphorylation of Akt and Erk, but not p38, upon FLT3 ligand (FL) stimulation. Stem cell factor (SCF)-mediated Akt and Erk activation was also elevated by CSK inhibition. However, siRNA mediated CSK knockdown increased SCF stimulated Akt phosphorylation but decreased Erk phosphorylation. CSK depletion also significantly increased both FL- and SCF-induced SHC, Gab2 and SHP2 phosphorylation. Furthermore, CSK depletion contributed to oncogenic FLT3- and c-Kit-mediated cell proliferation, but not to cell survival. Thus, the results indicate that CSK association with type III RTKs, FLT3 and c-Kit can have differential impact on receptor downstream signaling.
authors.affiliation: Experimental Clinical Chemistry, Department of Laboratory Medicine, Wallenberg Laboratory, Lund University, Skåne University Hospital, 20502 Malmö, Sweden.
authors.forename: Julhash U
authors.initials: JU
authors.lastname: Kazi
authors.forename: Marica
authors.initials: M
authors.lastname: Vaapil
authors.forename: Shruti
authors.initials: S
authors.lastname: Agarwal
authors.forename: Enrico
authors.initials: E
authors.lastname: Bracco
authors.forename: Sven
authors.initials: S
authors.lastname: Påhlman
authors.forename: Lars
authors.initials: L
authors.lastname: Rönnstrand
mesh_terms: D000818:Animals; D019556:COS Cells; D000081247:CSK Tyrosine-Protein Kinase; D002460:Cell Line; D002522:Chlorocebus aethiops; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D060066:Protein Interaction Maps; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D054875:Ubiquitination; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D018909:src Homology Domains; D019061:src-Family Kinases / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; C084881:flt3 ligand protein; D019009:Proto-Oncogene Proteins c-kit; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases