Generation of rac3 Null Mutant Mice: Role of Rac3 in Bcr/Abl-Caused Lymphoblastic Leukemia

Abstract

Numerous studies indirectly implicate Rac GTPases in cancer. To investigate if Rac3 contributes to normal or malignant cell function, we generated rac3 null mutants through gene targeting. These mice were viable, fertile, and lacked an obvious external phenotype. This shows Rac3 function is dispensable for embryonic development. Bcr/Abl is a deregulated tyrosine kinase that causes chronic myelogenous leukemia and Ph-positive acute lymphoblastic leukemia in humans. Vav1, a hematopoiesis-specific exchange factor for Rac, was constitutively tyrosine phosphorylated in primary lymphomas from Bcr/Abl P190 transgenic mice, suggesting inappropriate Rac activation. rac3 is expressed in these malignant hematopoietic cells. Using lysates from BCR/ABL transgenic mice that express or lack rac3, we detected the presence of activated Rac3 but not Rac1 or Rac2 in the malignant precursor B-lineage lymphoblasts. In addition, in female P190 BCR/ABL transgenic mice, lack of rac3 was associated with a longer average survival. These data are the first to directly show a stimulatory role for Rac in leukemia in vivo. Moreover, our data suggest that interference with Rac3 activity, for example, by using geranyl-geranyltransferase inhibitors, may provide a positive clinical benefit for patients with Ph-positive acute lymphoblastic leukemia.

ACKNOWLEDGMENTS

We thank Michael Anderson and his lab for help, advice, and access to real-time PCR, Aljona Antipova for involvement in cloning murine rac3 genomic DNA, Jess Cunnick for help with optimizing lymphoma culture and imaging of the cells, Hyungtaek Lee for help with evaluation of rac3^−/− and rac3^+/+ mice injected with LPS, Dinithi Silva for assistance with construction of the targeting vector, Ana Romero for help with isolation of mouse tail DNAs, Donna Foster for excellent care of the mice, and Bianca Hemmeryckx for preparation of some of the lymphoma lysates. Gary Bokoch and Ulla Knaus (Scripps Research Institute, La Jolla, CA) are acknowledged for GST-Pak-RBD.

This work was supported by PHS grants CA50248 and CA90321 (N.H.), HL060231 and HL071945 (J.G.), the Kenneth T and Eileen L Norris Foundation (B.Z. and J.G.), and the T. J. Martell Foundation (J.G. and N.H.).