Immunohistochemical screening for oncogenic tyrosine kinase activation

Tyrosine kinases causing the abnormal phosphorylation of intracellular prot eins have been shown to contribute to oncogenic transformation in a number of human neoplasms. Immunohistological staining Of routine biopsy sections for increased levels of phosphotyrosine may therefore provide a simple mean s of screening for tumours containing activated tyrosine kinases. In this s tudy, monoclonal antibodies to phosphotyrosine were used to immunostain a c ell line and tumour biopsies from lymphomas known to contain the activated anaplastic-lymphoma-kinase (ALK) tyrosine kinase. A range of normal and oth er neoplastic tissues were also immunostained for comparison. An anaplastic large cell lymphoma(ALCL) cell line carrying the (2;5) translocation, whic h creates the activated nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) tyrosine kinase, was strongly labelled. Routine tissue biopsies from five c ases of ALK-positive ALCL were also strongly positive for phosphotyrosine. The characteristic granular cytoplasmic labelling pattern for phosphotyrosi ne observed in a B-cell lymphoma (expressing full length ALK kinase) was id entical to that obtained using an ALK-specific antibody, thus confirming th at labelling for phosphotyrosine in lymphoma fells reflects the presence of an activated kinase. When normal lymphoid tissues were stained, there was little or no labelling for phosphotyrosine,but stronger labelling was seen in other cells and tissues; for example, endothelial cells and some carcino ma samples. Whilst the strong labelling for phosphotyrosine observed in the lymphoma cells is due to the presence of activated ALK, the strong stainin g of some normal cells presumably represents physiologically active kinases and this should be taken into account when interpreting the immunostaining of non-lymphoid tumours. The simplicity of this method, however, means tha t it offers a new rapid approach to the screening of large numbers of tumou rs for the presence of aberrant tyrosine kinase activation, particularly if they arise from tissues which normally contain only background levels of p hosphotyrosine, Copyright (C) 1999 John Wiley & Sons, Ltd.