A new variant anaplastic lymphoma kinase (ALK)-fusion protein (ATIC-ALK) in a case of ALK-positive anaplastic large cell lymphoma

Anaplastic lymphoma kinase (ALK)-positive lymphomas ("ALKomas") constitute a distinct molecular and clinicopathological entity within the heterogeneou s group of CD30-positive large cell Lymphomas, In 80-85% of cases tumor cel ls express a M-r 80,000 hybrid protein comprising the nucleolar phosphoprot ein nucleophosmin (NPM) and the ALK. We report here the cloning and express ion of a novel ALK-fusion protein from an ALK-positive lymphoma. This case was selected for molecular investigation because of (a) the absence of NPM- ALK transcripts; (b) the atypical staining patterns for ALK (cytoplasm-rest ricted) and for NPM (nucleus-restricted); and (c) the presence of a M-r 96, 000 ALK-protein differing in size from NPM-ALK, Nucleotide sequence analysi s of ALK transcripts isolated by 5'-rapid amplification of cDNA ends reveal ed a chimeric mRNA corresponding to an ATIC-ALK in-frame fusion. ATIC is a bifunctional enzyme (5-aminoimidazole-4-carboxamide ribonucleotide transfor mylase and IMP cyclohydrolase enzymatic activities) that catalyzes the penu ltimate and final enzymatic activities of the purine nucleotide synthesis p athway. Expression of full-length ATIC-ALK cDNA in mouse fibroblasts reveal ed that the fusion protein (a) possesses constitutive tyrosine kinase activ ity; (b) forms stable complexes with the signaling proteins Grb2 and Shc; ( c) induces tyrosine-phosphorylation of Shc; and (d) provokes oncogenic tran sformation. These findings point to fusion with ATIC as an alternative mech anism of ALK activation.