SHP-2 phosphatase is required for hematopoietic cell transformation by Bcr-Abl

Abstract

SHP-2 phosphatase forms a stable protein complex with and is heavily tyrosine-phosphorylated by the oncogenic tyrosine kinase Bcr-Abl. However, the role of SHP-2 in Bcr-Abl-mediated leukemogenesis is unclear. In the present report, we provide evidence that SHP-2 is required for hematopoietic cell transformation by Bcr-Abl. In vitro biological effects of Bcr-Abl transduction were diminished in SHP-2 ⌬/⌬ hematopoietic cells, and the leukemic potential of Bcr-Abltransduced SHP-2 ⌬/⌬ cells in recipient animals was compromised. Further analyses showed that Bcr-Abl protein (p210) was degraded, and its oncogenic signaling was greatly decreased in SHP-2 ⌬/⌬ cells. Treatment with proteasome inhibitors or reintroduction of SHP-2 restored p210 level in Bcr-Abl-transduced SHP-2 ⌬/⌬ cells. Subsequent investigation revealed that SHP-2 interacted with heat shock protein 90, an important chaperone protein protecting p210 from proteasome-mediated degradation. The role of SHP-2 in the stability of p210 is independent of its catalytic activity. Blockade of SHP-2 expression in p210-expressing cells by antisense or small-interfering RNA approaches decreased p210 level, causing cell death. Inhibition of SHP-2 enzymatic activity by overexpression of catalytically inactive SHP-2 mutant did not destabilize p210 but enhanced serum starvationinduced apoptosis, suggesting that SHP-2 also plays an important role in downstream signaling of p210 kinase. These studies identified a novel function of SHP-2 and suggest that SHP-2 might be a useful target for controlling Bcr-Abl-positive leukemias. IntroductionChronic myeloid leukemia (CML) is a clonal hematopoietic cell malignancy associated with the reciprocal t(9;22)(q34;q11) chromosome translocation. 1,2 Translocation of c-Abl located on chromosome 9 to the breakpoint-cluster region (Bcr) on chromosome 22 generates a fusion oncogene Bcr-Abl, which primarily produces the chimeric tyrosine kinase p210. 3 Because of fusion of the autoinhibitory SH3 domain of c-Abl to Bcr, autoinhibition of Abl kinase by its SH3 domain is disrupted. As a result, the chimeric kinase is constitutively activated. [4][5][6] Constitutively active p210 kinase appears to play a fundamental role as the primary causative factor in CML. The presence of this kinase is essential and sufficient for malignant transformation of hematopoietic cells in culture, 7,8 and expression of p210 in transgenic mice causes a CML-like myeloproliferative disease. 9,10 Treatment of Bcr-Abl-transformed hematopoietic cells with potent inhibitors of the p210 kinase, such as Gleevec (also known as imatinib mesylate or STI-571) [11][12][13]14 leads to growth inhibition and apoptosis. The therapeutic efficacy of imatinib mesylate has been demonstrated in patients with CML. 12,13 Although biological effects mediated by Bcr-Abl tyrosine kinase have been extensively characterized, the molecular mechanisms by which the oncogenic kinase transforms hematopoietic cells are not fully understood. Bcr-Abl kinase induces hematopoietic cell transformation by a...

Charting the molecular network of the drug target Bcr-Abl

“…These included spectrin-␣, 2 of the catalytic subunits of phosphatidylinositol-3-kinase (p110␣ and p110␤), the SH2-domain containing tyrosine phosphatase SHP-2, the tyrosine kinase Csk, the Grb2 adapter binding protein Gab2, and the guanine nucleotide exchange factor Sos1. Many of these proteins are protooncogenes and have been described to form critical links to downstream signaling pathways (p110␣/␤ for the PI3K/Akt pathway; Sos1, Gab2, and SHP-2 for the Ras/MAPK pathway) and were shown to be necessary for Bcr-Abl dependent transformation, e.g., SHP-2 and Gab2 (39,40).…”

Shp2, a novel oncogenic tyrosine phosphatase and potential therapeutic target for human leukemia

“…Over the past few years, a number of disease-associated Shp2 mutants have been identified in human leukemia and other malignancies [1,3,4]. Recently, studies from our laboratories and others strongly suggest that dysregulation of wild-type Shp2 enzyme may be involved in the pathogenesis of adult leukemia [4][5][6][7]. These findings not only provide new insights into the role of Shp2 in leukemogenesis and other tumors, but also suggest new therapeutic targets for anti-leukemia drugs.…”

“…Chen and co-workers reported that blockade of Shp2 expression in p210-expressing cells by antisense or small-interfering RNA approaches decreased p210 level, causing cell death. Inhibition of Shp2 enzymatic activity by overexpression of catalytically inactive Shp2 mutant did not destabilize p210 but enhanced serum starvation-induced apoptosis, suggesting that Shp2 also plays an important role in downstream signaling of the p210 kinase [5]. Interestingly, 8-hydroxy-7-(6-sulfonaphthalen-2-yl) diazenyl-quinoline-5-sulfonic acid (NSC-87877) has been identified as a small molecule with a potent inhibition effect on Shp2 protein-tyrosine phosphatase [10].…”

“…A recent study reported that Shp2 is required for hematopoietic cell transformation by Bcr-Abl [5]. In vitro biological effects of Bcr-Abl transduction were diminished in Shp2Delta/Delta hematopoietic cells, and the leukemic potential of Bcr-Abltransduced Shp2Delta/Delta cells in recipient animals was compromised.…”

“…Further analyses showed that the Bcr-Abl protein (p210) was degraded, and its oncogenic signaling was greatly decreased in Shp2Delta/Delta cells. Subsequent investigation revealed that Shp2 interacted with heat shock protein 90, an important chaperone protein protecting p210 from proteasome-mediated degradation [5].…”