Activation of the gene for the PDGF receptor beta1 (PDGFRbeta) in interleukin-3-dependent myeloid cells by retroviral insertional mutagenesis: implications for the transforming potential of PDGFRbeta

Retroviral insertional mutagenesis has proven to be a powerful tool to identify genetic lesions disrupting normal hematopoiesis. The gene encoding the beta receptor for platelet-derived growth factor (PDGFRbeta) was identified as a target of retroviral mutagenesis in mutants selected for interleukin-3 (IL3)-independent growth. Expression of PDGFRbeta in the parental cells using a retroviral vector increased the frequency of factor-independent growth, confirming the significance of the retroviral integration site. Significantly, however, expression of the receptor did not induce IL3-independent growth in one step. In contrast, TEL-PDGFRbeta, the fusion protein generated by the t(5;12) translocation associated with chronic myelomonocytic leukemia, induced factor-independent growth in all transductants, demonstrating that the TEL-PDGFRbeta fusion protein is a more potent mitogenic signal. Nevertheless PDGFRbeta overexpression is sufficient to give a selective advantage to IL3-dependent cells under adverse conditions, allowing the selection of secondary mutations that impart IL3-independent growth. These results underline the power of insertional mutagenesis to identify subtle but initiating mutations that synergize with other lesions in oncogenic transformation.