The absence of a novel intron 19-retaining ALK transcript (ALK-I19) and MYCN amplification correlates with an excellent clinical outcome in neuroblastoma patients.

Abdulraheem Alshareef,Nidhi Gupta,Hai-Feng Zhang,Sadeq Al-Dandan,Scott D Findlay,Moinul Haque,Raymond Lai,Justine Lai,Bo Kyung Alex Seong,Meredith S Irwin,Mohammed Rayis

doi:10.18632/oncotarget.24216

Abstract

ALK missense mutations are detected in 8% of neuroblastoma (NB) tumors at diagnosis and confer gain-of-function oncogenic effects. The mechanisms by which the expression of wild-type or mutant ALK, which is detectable in the majority of cases, is regulated are not well understood. We have identified a novel ALK transcript characterized by the retention of intron 19 (ALK-I19). ALK-I19 was detected in 4/4 NB cell lines, but not other non-NB cells with ALK aberrations. The functional significance of ALK-I19 was determined by specific siRNA knockdown of this transcript, which resulted in substantially decreased expression of the fully-spliced ALK transcripts (FS-ALK) and a significant reduction in cell growth. We also demonstrate that ALK-I19 is a precursor of FS-ALK. ALK-I19 was detected in 14/37 (38%) tumors from patients with newly diagnosed NB. ALK-I19 expression correlated with undifferentiated histology and strong ALK protein expression detectable by immunohistochemistry. Importantly, patients with tumors that did not express ALK-I19 and lacked MYCN amplification had an excellent clinical outcome, with 19/19 patients survived at 5-years. In conclusion, ALK-I19 is a novel ALK transcript that likely represents a marker of undifferentiated NB cells. The absence of ALK-I19 and MYCN amplification is a useful prognostic marker for NB patients.

Highlights

Anaplastic lymphoma kinase (ALK), which encodes a tyrosine kinase member of the insulin receptor superfamily, was initially identified as a potent oncogenic driver in anaplastic large-cell lymphoma (ALCL) [1, 2]
We were interested in the intron 19 region (I19) of ALK, since portions of I19 have been found in the mRNA transcripts of two ALK fusion genes, EML4-ALK and PPFIBP1-ALK, detectable in lung cancer and myofibroblastoma, respectively [18,19,20,21,22]
The key finding of this study is the identification of a novel ALK transcript, ALK-I19, which was detectable in 4/4 NB cell lines and in 38% of our cohort of NB tumors at time of diagnosis

Summary

Introduction

Anaplastic lymphoma kinase (ALK), which encodes a tyrosine kinase member of the insulin receptor superfamily, was initially identified as a potent oncogenic driver in anaplastic large-cell lymphoma (ALCL) [1, 2]. In ALCL, the tyrosine kinase of ALK is constitutively active, and this is directly resulted from the reciprocal chromosomal translocations fusing the portion of ALK that encodes the tyrosine kinase domain and different gene partners, with the nucleophosmin (NPM) gene being the most frequently implicated [2]. Other than ALCL, ALK genetic alterations were identified in a variety of tumors including neuroblastoma (NB), myofibroblastoma and non-small cell lung cancer (NSCLC) [3] These genetic alterations include chromosomal translocations involving fusion partners other than NPM, gene amplification and activating missense mutations, all of which are believed to result in constitutive activation of the ALK tyrosine kinase and the downstream cellular signaling pathways and biological processes [3]. In keeping with the pathogenetic importance of ALK in these human cancers, targeted inhibition of ALK using various tyrosine kinase inhibitors have shown therapeutic efficacy against subsets of ALK-positive tumors [3]

Methods

Results

Conclusion