title: CD45 tyrosine phosphatase inhibits erythroid differentiation of umbilical cord blood CD34+ cells associated with selective inactivation of Lyn.
abstract: CD45 is a membrane-associated tyrosine phosphatase that dephosphorylates Src family kinases and Janus kinases (JAKs). To clarify the role of CD45 in hematopoietic differentiation, we examined the effects of anti-CD45 monoclonal antibody NU-L(PAN) on the proliferation and differentiation of umbilical cord blood CD34(+) cells. NU-L(PAN) showed a prominent inhibition of the proliferation of CD34(+) cells induced by the mouse bone marrow stromal cell line MS-5 or erythropoietin (EPO). However, NU-L(PAN) did not affect the proliferation induced by interleukin 3. NU-L(PAN) also inhibited MS-5-induced or EPO-induced erythroid differentiation of CD34(+) cells. The cells stimulated with EPO in the presence of NU-L(PAN) morphologically showed differentiation arrest at the stage of basophilic erythroblasts after 11 days of culture, whereas the cells treated with EPO without NU-L(PAN) differentiated into mature red blood cells. The Src family kinase Lyn and JAK2 were phosphorylated when erythroblasts obtained after 4 days of culture of CD34(+) cells in the presence of EPO were restimulated with EPO. Overnight NU-L(PAN) treatment before addition of EPO reduced the phosphorylation of Lyn but not that of JAK2. Simultaneously, the enhancement of Lyn kinase activity after restimulation with EPO was reduced by NU-L(PAN) treatment. These results indicate selective inactivation of Lyn by CD45 activated with NU-L(PAN) and could partly explain the inhibitory mechanism on erythropoiesis exhibited by EPO. These findings suggest that CD45 may play a pivotal role in erythropoiesis.
authors.affiliation: Fujisaki Cell Center, Hayashibara Biochemical Labs, and the Kurashiki Medical Center, Kurashiki, Okayama, Japan. fcch@hayashibara.co.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Harashima
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Suzuki
authors.forename: Ayumi
authors.initials: A
authors.lastname: Okochi
authors.forename: Mayuko
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Motoda
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Yoshioka
authors.forename: Kunzo
authors.initials: K
authors.lastname: Orita
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D018920:Coculture Techniques; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000187:drug effects; D004920:Erythropoiesis / Q000187:drug effects*; D004921:Erythropoietin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005312:Fetal Blood / Q000166:cytology*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D053614:Janus Kinase 2; D017493:Leukocyte Common Antigens / Q000276:immunology / Q000502:physiology*; D051379:Mice; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D017154:Stromal Cells / Q000166:cytology / Q000502:physiology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors*
chemical_list: D000911:Antibodies, Monoclonal; D007377:Interleukin-3; D011518:Proto-Oncogene Proteins; D004921:Erythropoietin; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases