Positive and negative regulatory roles of the WW-like domain in TEL-PDGF R transformation

TEL–platelet-derived growth factor– receptor (TEL-PDGF R) is expressed in chronic myelomonocytic leukemias associated with t(5;12)(q33;p13), and the fusion tyrosine kinase retains a conserved WW-like domain in the PDGF R autoinhibitory juxtamembrane region. Here we report that mutation of the 2 conserved tryptophan residues of the WW-like domain has opposing effects on TELPDGF R kinase activation. Alanine substitution of W593, essential for proteinprotein interaction in the context of other WW domains, impaired TEL-PDGF R– mediated transformation of hematopoietic cells due to inhibition of TEL-PDGF R kinase activity. In contrast, alanine substitution of W566, essential for structural integrity of WW domain in other contexts, had no effect on TEL-PDGF R activation and oncogenic activity. Surprisingly, however, the W566A mutation suppressed the W593A phenotype. Double mutant W566A/ W593A was indistinguishable from the wild-type fusion protein with regard to kinase activity, ability to confer factorindependent growth to Ba/F3 cells, or ability to induce a myeloproliferative disease in mice. Additional mutational analysis identified other substitutions within the WW-like domain in addition to W566A that could also suppress the W593A phenotype, including mutations predicted to diminish the autoinhibitory function of the juxtamembrane region. Therefore, the WW-like domain in the context of TELPDGF R may have both positive and negative regulatory roles in kinase activation. (Blood. 2004;104:535-542)