Pak and Rac GTPases promote oncogenic KIT–induced neoplasms
Holly Martin, Raghuveer Singh Mali, Peilin Ma, Anindya Chatterjee, Baskar Ramdas, Emily Sims, Veerendra Munugalavadla, Joydeep Ghosh, Ray R. Mattingly, Valeria Visconte, Ramon V. Tiu, Cornelis P. Vlaar, Suranganie Dharmawardhane, Reuben Kapur
Holly Martin, Raghuveer Singh Mali, Peilin Ma, Anindya Chatterjee, Baskar Ramdas, Emily Sims, Veerendra Munugalavadla, Joydeep Ghosh, Ray R. Mattingly, Valeria Visconte, Ramon V. Tiu, Cornelis P. Vlaar, Suranganie Dharmawardhane, Reuben Kapur
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Research Article Oncology

Pak and Rac GTPases promote oncogenic KIT–induced neoplasms

Abstract

An acquired somatic mutation at codon 816 in the KIT receptor tyrosine kinase is associated with poor prognosis in patients with systemic mastocytosis and acute myeloid leukemia (AML). Treatment of leukemic cells bearing this mutation with an allosteric inhibitor of p21–activated kinase (Pak) or its genetic inactivation results in growth repression due to enhanced apoptosis. Inhibition of the upstream effector Rac abrogates the oncogene-induced growth and activity of Pak. Although both Rac1 and Rac2 are constitutively activated via the guanine nucleotide exchange factor (GEF) Vav1, loss of Rac1 or Rac2 alone moderately corrected the growth of KIT-bearing leukemic cells, whereas the combined loss resulted in 75% growth repression. In vivo, the inhibition of Vav or Rac or Pak delayed the onset of myeloproliferative neoplasms (MPNs) and corrected the associated pathology in mice. To assess the role of Rac GEFs in oncogene-induced transformation, we used an inhibitor of Rac, EHop-016, which specifically targets Vav1 and found that EHop-016 was a potent inhibitor of human and murine leukemic cell growth. These studies identify Pak and Rac GTPases, including Vav1, as potential therapeutic targets in MPN and AML involving an oncogenic form of KIT.

Authors

Holly Martin, Raghuveer Singh Mali, Peilin Ma, Anindya Chatterjee, Baskar Ramdas, Emily Sims, Veerendra Munugalavadla, Joydeep Ghosh, Ray R. Mattingly, Valeria Visconte, Ramon V. Tiu, Cornelis P. Vlaar, Suranganie Dharmawardhane, Reuben Kapur

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Figure 3

In vivo inhibition of Rac prolongs survival and rescues myeloid cell infiltration associated with KITD814V-bearing mice.

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In vivo inhibition of Rac prolongs survival and rescues myeloid cell inf...
C3H/HeJ mice were transplanted with 2 million cells bearing KITD814V, with or without RacN17. (A) Kaplan-Meier survival analysis of syngeneic C3H/HeJ mice transplanted with cells bearing KITD814V (n = 16) or KITD814V plus RacN17 (n = 26). *P < 0.001 for KITD814V versus KITD814V plus RacN17. (B) White blood cell (WBC) and NE counts in mice bearing cells transplanted with KITD814V (n = 9) or KITD814V plus RacN17 (n = 12) and C3H/HeJ control mice (n = 5). *P < 0.05 for KITD814V versus KITD814V plus RacN17. Histopathologic analysis of spleen (C) and lung (D) from mice transplanted with cells bearing KITD814V alone or in combination with RacN17. Shown are representative tissue sections after fixing them in 10% buffered formalin, sectioning them, and staining them with H&E. Original magnification, ×10 (left panels), ×20 (center panels), and ×40 (right panels). Normal erythroid and myeloid components in lungs, liver, and spleen were replaced by leukemic cells in KITD814V-bearing mice, which were significantly rescued in tissues from mice bearing RacN17 along with KITD814V. (E) Cell lysates derived from spleens of mice described above were subjected to a Rac activity assay as described in Figure 2. Shown is the level of Rac1 GTP, Rac2 GTP, total Rac1, and total Rac2 in each lane from the indicated genotypes.