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The role of Ahi-1 and BCR-ABL in leukemic transformation Kennedy, Sean


Ahi-1 was first identified as an insertional target of Abelson virus in murine leukemias. Subsequently Ahi-1 was shown to encode a protein containing a SH3 domain and multiple WD40 repeats. Certain isoforms of Ahi-1 are upregulated in a variety of human leukemic cells, including primitive leukemic cells from patients with chronic myeloid leukemia. To investigate the types of effects that increased levels of Ahi-1 protein(s) may have on hematopoietic cells (both in the presence and absence of p210[superscript]BCR-ABL), I compared both the biological and biochemical properties of several cloned lines of BaF/3 cells that had been transduced with either BCR-ABL or Ahi-1 or both control vectors. Overexpression of Ahi-1 mimicked the effect of BCR-ABL in reducing the growth factor dependence of BaF/3 cells and in enhancing their growth in response to IL-3. The response of the doubly-transduced cells was even greater. However, of these many signalling intermediates surveyed by Western blot analysis, only a few showed significant changes. In cells transduced with Ahi-1 alone and cultured in the presence of IL-3 (but not in the absence of IL-3), STAT5 phosphorylation was increased. SHIP expression was also increased in the same cells but only when they were cultured in the absence of IL-3. In cells that had been co-transduced with BCR-ABL and Ahi-1, both the level and kinase activity of p210[superscript]BCR-ABL appe a r e (j enhanced and in these co-transduced cells, the known ability of BCR-ABL to suppress SHIP expression was dominant over the stimulating effect of overexpressing Ahi-1. Unexpectedly, BCR-ABL transduction of BaF/3 cells strongly upregulated their endogenous Ahi-1 expression. Taken together, these preliminary findings are consistent with a model in which Ahi-1 alone can behave as a weak oncogene in hematopoietic cells, and can also co-operate with BCR-ABL to enhance the combined effect achieved.

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