Functional analyses of mutations in receptor tyrosine kinase genes in non-small cell lung cancer: double-edged sword of DDR2

Purpose: This study investigated whether mutations of receptor tyrosine kinase (RTK) genes detected using next-generation sequencing (NGS) are suitable therapeutic targets. Experimental design: Fifty surgically resected NSCLC samples were target-resequenced using NGS. We then investigated the functions of the identified RTK gene mutations, including their oncogenic potential, in vitro. Results: Mutations in RTK genes were found in 20 samples (EGFR, 15; ERBB4, 1; ALK, 1; DDR2, 2; FGFR1, 1), mutations in MAPK pathway genes were found in 9 samples (KRAS, 7; NRAS, 1; BRAF, 2), and mutations in PI3K pathway genes were found in 3 samples (PIK3CA, 1; PTEN, 3). Among the mutations in RTKs, the functions of 4 mutations were unclear (ERBB4 D245G; DDR2 H246R and E655K; FGFR1 A263V). These mutations did not exhibit any transformational activities. Neither the phosphorylation nor the protein expressions of RTKs were changed by the DDR2 H246R, ERBB4 D245G, and FGFR1 A263V mutations, although the expression level of the DDR2 protein harboring the E655K mutation was particularly low. Collagen stimulation decreased cellular proliferation through p38 activation in the DDR2 wild-type-overexpressed cell lines, whereas the growth suppressive effect was weakened in DDR2 E655K-overexpressed cell lines. Furthermore, the DDR2 E655K protein strongly bound to ubiquitin ligase E3 (Cbl-b), and the mutant protein expression was increased after treatment with a proteasome inhibitor. Conclusion: Our experimental findings suggest that RTK mutations are not always suitable as therapeutic targets. The DDR2 E655K mutation can play a role in cancer progression by reducing the growth inhibitory effect of collagen.

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