Monitoring signal transduction in cancer: Tyrosine kinase gene expression profiling

Abnormal expression of tyrosine kinase (TK) genes is common in tumors, in w hich it is believed to alter cell growth and response to external stimuli s uch as growth factors and hormones. Although the etiology and pathogenesis of carcinomas of the thyroid or breast remain unclear, there is evidence th at the expression of TK genes, such as receptor tyrosine kinases, or mitoge n-activated protein kinases, is dysregulated in these tumors, and that over expression of particular TK genes due to gene amplification, changes in gen e regulation, or structural alterations leads to oncogenic transformation o f epithelial cells. We developed a rapid scheme to measure semiquantitative ly the expression levels of 50-100 TK genes. Our assay is based on RT-PCR w ith mixed based primers that anneal to conserved regions in the catalytic d omain of TK genes to generate gene-specific fragments. PCR products are the n labeled by random priming and hybridized to DNA microarrays carrying know n TK gene targets. Inclusion of differently labeled fragments from referenc e or normal cells allows identification of TK genes that show altered expre ssion levels during malignant transformation or tumor progression. Examples demonstrate how this innovative assay might help to define new markers for tumor progression and potential targets for disease intervention.