KIF5B-ALK, a Novel Fusion Oncokinase Identified by an Immunohistochemistry-based Diagnostic System for ALK-positive Lung Cancer

The Cancer Institute, Japanese Foundation for Cancer Research, Japan.
Clinical Cancer Research (Impact Factor: 8.72). 05/2009; 15(9):3143-9. DOI: 10.1158/1078-0432.CCR-08-3248
Source: PubMed


EML4-ALK is a transforming fusion tyrosine kinase, several isoforms of which have been identified in lung cancer. Immunohistochemical detection of EML4-ALK has proved difficult, however, likely as a result of low transcriptional activity conferred by the promoter-enhancer region of EML4. The sensitivity of EML4-ALK detection by immunohistochemistry should be increased adequately.
We developed an intercalated antibody-enhanced polymer (iAEP) method that incorporates an intercalating antibody between the primary antibody to ALK and the dextran polymer-based detection reagents.
Our iAEP method discriminated between tumors positive or negative for EML4-ALK in a test set of specimens. Four tumors were also found to be positive for ALK in an archive of lung adenocarcinoma (n = 130) and another 4 among fresh cases analyzed in a diagnostic laboratory. These 8 tumors were found to include 1 with EML4-ALK variant 1, 1 with variant 2, 3 with variant 3, and 2 with previously unidentified variants (designated variants 6 and 7). Inverse reverse transcription-PCR analysis revealed that the remaining tumor harbored a novel fusion in which intron 24 of KIF5B was ligated to intron 19 of ALK. Multiplex reverse transcription-PCR analysis of additional archival tumor specimens identified another case of lung adenocarcinoma positive for KIF5B-ALK.
The iAEP method should prove suitable for immunohistochemical screening of tumors positive for ALK or ALK fusion proteins among pathologic archives. Coupling of PCR-based detection to the iAEP method should further facilitate the rapid identification of novel ALK fusion genes such as KIF5B-ALK.

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    • ". The intercalated antibody-enhanced polymer method was used for the sensitive detection of ALK, as described previously (Takeuchi et al., 2009). "
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    • "The rearrangement results from a short inversion in chromosome 2p, whereby ALK signaling is activated by the creation of oncogenic fusions of the intron 10 of ALK gene within an upstream partner intron 13 of echinoderm microtubule associated protein-like 4 (EML4)6. More recently, less than 1% of ALK rearrangements cases have different partner genes including kinesin family member 5B (KIF5B), TFG, and KLC-111,18. ALK rearrangements occur in approximately 4% of lung adenocarcinoma patients, usually young, non-smokers with clinically advanced disease6,7,8. "
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    • "Together with dimerization through the coiled-coil domain, the RET tyrosine kinase activity of the fusion protein may be activated aberrantly, thus facilitating oncogenesis in the lung. This hypothesis corroborates the oncogenic mechanism proposed for the fusion gene KIF5B-ALK, in which the coiled-coil domain of KIF5B is always preserved, and its constitutive expression in lung is believed to activate ALK and downstream oncogenic effects [30,33]. "
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