title: Lyn kinase and ZAP70 are substrates of PTPROt in B-cells: Lyn inactivation by PTPROt sensitizes leukemia cells to VEGF-R inhibitor pazopanib.
abstract: We have recently shown that the gene encoding the truncated form of protein tyrosine phosphatase receptor-type O (PTPROt) expressed predominantly in hematopoietic cells is epigenetically silenced in human primary chronic lymphocytic leukemia (B-CLL). To determine whether increased phosphorylation of the PTPROt substrates following PTPROt suppression alters signal transduction pathway(s) that impart a growth advantage to the leukemic lymphocytes, it is critical to discern the key substrates of PTPROt. Here, we used substrate-trapping assay to identify two novel substrates of PTPROt, the tyrosine kinases Lyn and ZAP70. Both Lyn and ZAP70 were dephosphorylated by wild-type PTPROt, but not by its catalytic site (CS) mutant. A critical phosphorylation site in Lyn, Y397, essential for its activity was dephosphorylated by PTPROt. Consequently, the activity of Lyn kinase was compromised when co-expressed with PTPROt-WT compared to vector control or upon co-expression with PTPROt-CS. Ectopic expression of PTPROt in Raji cells reduced phosphorylation of Lyn in the absence of any change in its protein levels. These results have revealed the physiological importance of PTPROt in regulating B-cell receptor signaling at Lyn kinase. Further, ectopic expression of PTPROt also sensitized the cells to the VEGF-R inhibitor Pazopanib.
authors.affiliation: Department of Molecular and Cellular Biochemistry, College of Medicine, Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Tasneem
authors.initials: T
authors.lastname: Motiwala
authors.forename: Jharna
authors.initials: J
authors.lastname: Datta
authors.forename: Huban
authors.initials: H
authors.lastname: Kutay
authors.forename: Satavisha
authors.initials: S
authors.lastname: Roy
authors.forename: Samson T
authors.initials: ST
authors.lastname: Jacob
mesh_terms: D001402:B-Lymphocytes / Q000201:enzymology / Q000378:metabolism*; D001483:Base Sequence; D015153:Blotting, Western; D020134:Catalytic Domain; D045744:Cell Line, Tumor; D017931:DNA Primers; D006801:Humans; D007191:Indazoles; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D010766:Phosphorylation; D011743:Pyrimidines / Q000494:pharmacology*; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3 / Q000378:metabolism*; D040262:Receptors, Vascular Endothelial Growth Factor / Q000037:antagonists & inhibitors*; D013379:Substrate Specificity; D013449:Sulfonamides / Q000494:pharmacology*; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000378:metabolism*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D007191:Indazoles; D011743:Pyrimidines; D013449:Sulfonamides; C516667:pazopanib; D040262:Receptors, Vascular Endothelial Growth Factor; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3