Abstract
Mutations in the kinase domain of the ALK kinase have emerged recently as important players in the genetics of the childhood tumor neuroblastoma. Here, we report the appearance of a novel ALK mutation in neuroblastoma, correlating with aggressive tumor behavior. Analyses of genomic DNA from biopsy samples initially showed ALK sequence to be wild type. However, during disease progression, mutation of amino acid F1174 to a serine within the ALK kinase domain was observed, which correlated with aggressive neuroblastoma progression in the patient. We show that mutation of F1174 to serine generates a potent gain-of-function mutant, as observed in 2 independent systems. First, PC12 cell lines expressing ALK(F1174S) display ligand-independent activation of ALK and further downstream signaling activation. Second, analysis of ALK(F1174S) in Drosophila models confirms that the mutation mediates a strong, rough eye phenotype upon expression in the developing eye. Thus, we report a novel ALK(F1174S) mutation that displays ligand-independent activity in vivo, correlating with rapid and treatment-resistant tumor growth. The study also shows that initial screening in the first tumor biopsy of a patient may not be sufficient and that further molecular analysis, in particular in tumor progression and/or tumor relapse, is warranted for better understanding of the treatment of neuroblastoma patients.
Highlights
The ALK gene (OMIM: 105590) was initially characterized as a fusion partner of the NPM-ALK oncogene and is recognized as the active component in multiple fusion proteins in a variety of cancers [1]
We have identified a novel activating mutation in ALK in a neuroblastoma patient in the course of analysis of genomic DNA from patient biopsy samples
In inducible cell lines expressing the F1174 ALK mutant as well as in the Drosophila model system, we are able to show that the F1174 ALK variant is potently activated in the absence of ligand stimulation, leading to the activation of downstream signaling events
Summary
The ALK gene (OMIM: 105590) was initially characterized as a fusion partner of the NPM-ALK oncogene and is recognized as the active component in multiple fusion proteins in a variety of cancers [1]. The very rapid progress of the tumor and development of refractoriness to chemotherapy coincided with the acquirement of a homozygous ALK tyrosine kinase domain mutation not present in the germline DNA of the patient (Fig. 2). Ectopic expression of human UAS-ALK in the Drosophila eye employing the pGMR-Gal4 driver line, which directs protein expression in the developing photoreceptors of the eye, does not result in any obvious phenotype in adult flies (Fig. 3B and F) and is similar to wild-type controls (Fig. 3A and E).
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