c-kit ligand stimulates tyrosine phosphorylation of a similar pattern of phosphotyrosyl proteins in primary primitive normal hematopoietic progenitors that are constitutively phosphorylated in comparable primitive progenitors in chronic phase chronic myelogenous leukemia.
Characteristic of Philadelphia (Ph)+ chronic myelogenous leukemia (CML) is the presence of the chimeric BCR/ABL (p210) protein possessing elevated protein tyrosine kinase activity relative to the normal c-abl tyrosine kinase. Our previous studies demonstrated subtle differences in the growth, phenotypic and morphologic characteristics of the most primitive subpopulations of primary lin-Ph+ chronic phase CML blasts and comparable primary lin- normal blasts. Recently, in comparing proteins phosphorylated on tyrosine in these cell populations, we reported a prominent 62 kDa phosphotyrosyl (P-tyr) protein constitutively present in primary primitive lin- CML chronic phase blasts which was virtually undetectable in primary primitive lin- normal blasts. In the present studies, we demonstrate that this P-tyr p62 from primary primitive lin- chronic phase CML blasts co-immunoprecipitates with ras-GAP. Furthermore, in addition to the p210 protein, we show in whole cell lysates the presence of other clearly consistent but less prominent P-tyr proteins with molecular weights of approximately 155, 140, 110, 55 and 45 kDa as well as more minor P-tyr proteins of approximately 190, 85, 52, 42 and 39 kDa constitutively present in primary primitive lin- chronic phase CML blasts. In analyzing proteins tyrosine phosphorylated in primary primitive lin- normal blasts in response to various hematopoietic growth factors, we found a striking similarity in the phosphorylation of four major (approximately 140, 110, 62 and 56 kDa) and three minor (approximately 51, 45 and 42 kDa) P-tyr proteins after stimulation with c-kit ligand and the P-tyr proteins constitutively phosphorylated in primary primitive lin- chronic phase CML blasts. Other growth factors tested (ie GM-CSF, G-CSF, IL-3, FLT3 ligand and EPO) were much less active or stimulated phosphorylation of other proteins. It is provocative that at least seven proteins rapidly and transiently phosphorylated on tyrosine in the c-kit ligand signal transduction pathway in lin- normal blasts may be constitutive substrates for the p210 activated tyrosine kinase in comparable lin- chronic phase CML blasts. In addition, it is intriguing that some of the biological effects on hematopoietic progenitors attributed to the c-kit ligand may be similar to some of the observed biological consequences of the p210 protein, including survival and expansion of a more mature stem cell population, probably at the time of lineage commitment rather than at the level of the earliest self-renewing stem cell.
Wisniewski
D
D
Sloan-Kettering Institute for Cancer Research, New York, USA.
Strife
A
A
Berman
E
E
Clarkson
B
B
D019070:Cell Lineage; D004591:Electrophoresis, Polyacrylamide Gel; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism; D020690:GTPase-Activating Proteins; D016298:Hematopoietic Cell Growth Factors / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D015151:Immunoblotting; D015466:Leukemia, Myeloid, Chronic-Phase / Q000378:metabolism* / Q000473:pathology; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism*; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism*; D020703:ras GTPase-Activating Proteins
D020690:GTPase-Activating Proteins; D016298:Hematopoietic Cell Growth Factors; D011506:Proteins; D019089:Stem Cell Factor; D020703:ras GTPase-Activating Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D016044:Fusion Proteins, bcr-abl