H4(D10S170), a gene frequently rearranged in papillary thyroid carcinoma, is fused to the platelet-derived growth factor receptor beta gene in atypical chronic myeloid leukemia with t(5;10)(q33;q22)

The molecular cloning of the t(5;10)(q33; q22) associated with atypical chronic myeloid leukemia (CML) is reported. Fluorescence in situ hybridization (FISH), Southern blot, and reverse transcriptase-polymerase chain reaction analysis demonstrated that the translocation resulted in an H4/platelet-derived growth factor receptor βR (PDGFβR) fusion transcript that incorporated 5′ sequences from H4 fused in frame to 3′ PDGFβR sequences encoding the transmembrane, WW-like, and tyrosine kinase domains. FISH combined with immunophenotype analysis showed that t(5;10)(q33;q22) was present in CD13 + and CD14 + cells but was not observed in CD3 + or CD19 + cells. H4 has previously been implicated in pathogenesis of papillary thyroid carcinoma as a fusion partner of RET. The H4/RET fusion incorporates 101 amino acids of H4, predicted to encode a leucine zipper dimerization domain, whereas the H4/PDGFβR fusion incorporated an additional 267 amino acids of H4. Retroviral transduction of H4/PDGFβR, but not a kinase-inactive mutant, conferred factor-independent growth to Ba/F3 cells and caused a T-cell lymphoblastic lymphoma in a murine bone marrow transplantation assay of transformation. Mutational analysis showed that the amino-terminal H4 leucine zipper domain (amino acids 55-93), as well as H4 amino acids 101 to 386, was required for efficient induction of factor-independent growth of Ba/F3 cells. Tryptophan-to-alanine substitutions in the PDGFβR WW-like domain at positions 566/593, or tyrosine-to-phenylalanine substitutions at PDGFβR positions 579/581 impaired factor-independent growth of Ba/F3 cells. H4/PDGFβR is an oncoprotein expressed in t(5;10)(q33;q22) atypical CML and requires dimerization motifs in the H4 moiety, as well as residues implicated in signal transduction by PDGFβR, for efficient induction of factor-independent growth of Ba/F3 cells.