¹Department of Haematology, Faculty of Medicine, Imperial College, Hammersmith Campus, London, UK

Correspondence: Professor MY Gordon, Department of Haematology, Faculty of Medicine, Imperial College, Hammersmith Campus, London W12 0NN, UK. E-mail: myrtle.gordon@imperial.ac.uk

Received 30 August 2007; Revised 18 October 2007; Accepted 5 November 2007; Published online 6 December 2007.

Abstract

We analysed the subcellular distribution of p210^BCR-ABL protein using a junction-specific anti-BCR-ABL monoclonal antibody and confocal laser scanning microscopy (CLSM). Our studies have shown that p210^BCR-ABL is arranged in discrete foci in the cytoplasm of cell lines and primary CD34⁺ cells but not mononuclear cells suggesting the foci may be a feature of immature chronic myeloid leukaemia cells. We have devised a strategy to score the foci and found the mean number of foci varies between the cell types. The number of foci per cell is directly related to the level of p210^BCR-ABL expression. CLSM was also used to analyse the distribution and colocalization of CT10 regulator-like (CRKL) p210^BCR-ABL. CRKL-p210^BCR-ABL foci were completely or partially associated, touching or separate in different regions of the same cell. We also analysed the distribution of phosphorylated CRKL (pCRKL) with p210^BCR-ABL and unexpectedly found only a small proportion of pCRKL in complex with p210^BCR-ABL. The foci distribution and high levels of uncomplexed p210^BCR-ABL, pCRKL and CRKL protein suggested the possibility of a dynamic equilibrium. Imatinib promoted nuclear transport of p210^BCR-ABL-positive foci. It also disrupted complex formation between p210^BCR-ABL and casitas B-cell lymphoma and CRKL but not between p210^BCR-ABL and GRB2. Our observations of the CRKL and p210^BCR-ABL complex may be important for understanding the function of CRKL.