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

Abstract

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). 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. 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. These data bear implications for the role of Shc-MAP kinase pathway in normal hemopoiesis and AML leukemogenesis.