Expression and activation of SHC/MAP kinase pathway in primary acute myeloid leukemia blasts

Introduction: We report the results of a study investigating signaling proteins in 26 cases of primary acute myelogenous leukemia. We studied the Shc adaptor proteins p52/p46Shc, which can activate the RAS/Mitogen Activated Protein kinase pathway, p66Shc which is uncoupled from RAS/MAP kinases and the MAP kinase family members Extracellular signal Regulated Kinase (ERK) and c-Jun NH2-terminal protein Kinase (JNK) or Stress Activated Protein Kinase (SAPK). Material and methods: CD34⁺ and CD34^- fractions of four human normal bone marrow and unfractionated bone marrow samples were investigated. Immunoblottings, immunoenzymatic and in vitro assays were performed. Results: Shc protein isoforms were constitutively expressed in all the AML cases examined. Tyrosine-phosphorylation of p53/p46Shc isoforms were found in CD34⁺ but not in the majority of CD34^- cases. p66Shc isoform was not tyrosine-phosphorylated in CD34^-, and was tyrosine-phosphorylated only in some CD34⁺ cases. Expression and activation of ERK was constitutively present in the majority of AML patients analysed. JNK/SAPK was expressed but not activated in the AMLs examined. Activation occurred after treatment of the leukemic cells by anisomycin, etoposide, and cytarabine. ERK and JNK/SAPK activation were not detectable in the hematopoietic precursors of human normal bone-marrow. Conclusion: These data bear implications for the role of Shc-MAP kinase pathway in normal hemopoiesis and AML leukemogenesis.