Loss of Growth Arrest DNA Damage 45a,b (GADD45a,b) Enhances Oncogenicity in BCR/ABL-Driven Chronic Myelogenous Leukemia.

Abstract 3264

Poster Board III-1

The bcr/abl oncogene causes chronic myelogenous leukemia (CML) in human. BCR/ABL induces the transformation of myeloid lineage through MAPK, JNK/SAPK, PI3K signaling pathways. Growth arrest DNA damage 45A (GADD45A) and GADD45B are upregulated during myeloid lineage terminal differentiation. They are involved in G2/M cell cycle arrest and apoptosis in response to exogenous stress stimuli through MAPK and JNK/SAPK pathways. To investigate the effect of GADD45A and GADD45B in the development of CML, syngeneic wild type lethally irradiated mice were reconstituted with wild type, gadd45a or gadd45b null myeloid progenitors transduced with a retrovirally expressed 210-kD BCR/ABL fusion oncoprotein. We found that loss of gadd45a or gadd45b accelerated the development of CML-like disease in wild type recipients. BCR/ABL transformed gadd45a or gadd45b deficient progenitor recipients exhibited a significantly accelerated kinetics of increase in the number of WBC and percentage of myeloid blasts in blood compared to mice reconstituted with the same number of wild type bone marrow cells transduced with BCR/ABL. There was also increase in the rate of accumulation of CD11b+Gr1+ cells in the bone marrow and spleen. Using in vitro and in vivo BrdU assays, enhanced proliferation capacity was observed for both BCR/ABL transduced gadd45a and gadd45b deficient myeloid progenitors. BCR/ABL transduced gadd45a and gadd45b deficient primary myeloid progenitors formed more and bigger colonies compared to BCR/ABL transformed wild type progenitors. Impaired apoptosis was showed in BCR/ABL transduced gadd45a deficient myeloid progenitors. These results indicate that both gadd45a and gadd45b function as suppressors of the development of BCR/ABL driven CML, where gadd45a appears to suppress CML via mechanism involving inhibition of cell proliferation enhancement of apoptosis, whereas gadd45b appears to only inhibit cellular proliferation. Dissecting the molecular nature of signaling paths involved in the suppressive function of gadd45a and gadd45b in BCR/ABL driven CML, as well as analysis of Gadd45 in CML patients, is underway.