elafin and Leukemia--Myeloid

Shp2 has been known to mediate growth factor-stimulated cell proliferation, but its role in cell survival is less clear. Gain-of-function Shp2 mutants such as Shp2E76K are associated with myeloid leukemias. We found that Shp2E76K could transform cytokine-dependent human TF-1 myeloid cells into cytokine independence and further characterized the Shp2E76K-induced cell survival mechanism in this study. Expression of Shp2E76K suppressed the cytokine withdrawal-induced intrinsic/mitochondrial apoptosis pathway, which is controlled by the Bcl-2 family proteins. Analysis of Bcl-2 family proteins showed that Bcl-XL and Mcl-1 were up-regulated in Shp2E76K-transformed TF-1 (TF-1/Shp2E76K) cells. Knockdown of Bcl-XL but not Mcl-1 with short hairpin RNAs prevented Shp2E76K-induced cytokine-independent survival. Roscovitine, which down-regulated Mcl-1, also did not prevent cytokine-independent survival of TF-1/Shp2E76K cells, whereas the Bcl-XL inhibitor HA14-1 did. Ras and mitogen-activated protein kinases Erk1 and Erk2 (Erk1/2) were constitutively activated in TF-1/Shp2E76K cells, whereas little active Akt was detected under cytokine-free conditions. Shp2E76K-induced Bcl-XL expression was suppressed by Mek inhibitors and by a dominant-negative Mek1 mutant but not by the phosphoinositide 3-phosphate inhibitor LY294002 and the Akt inhibitor API-2. Inhibition of Erk1/2 blocked cytokine-independent survival of TF-1/Shp2E76K cells, whereas inhibition of Akt had a minimal effect on cytokine-independent survival of TF-1/Shp2E76K cells. These results show that Shp2E76K can evoke constitutive Erk1/2 activation in TF-1 cells. Furthermore, Shp2E76K induces cytokine-independent survival of TF-1 cells by a novel mechanism involving up-regulation of Bcl-XL through the Erk1/2 pathway.

Topics: Amino Acid Substitution; Apoptosis; bcl-X Protein; Benzopyrans; Cell Line; Cell Survival; Chlorpropamide; Chromones; Down-Regulation; Elafin; Enzyme Activation; Granulocyte-Macrophage Colony-Stimulating Factor; Humans; Interleukin-3; Leukemia, Myeloid; MAP Kinase Signaling System; Mitochondria; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Morpholines; Mutation, Missense; Myeloid Cell Leukemia Sequence 1 Protein; Myeloid Progenitor Cells; Neoplasm Proteins; Nitriles; Oncogene Protein p21(ras); Protein Kinase Inhibitors; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-bcl-2; Purines; Roscovitine; Up-Regulation