Novel germline mutation in the transmembrane domain of HER2 in familial lung adenocarcinomas

Abstract

We encountered a family of Japanese descent in which multiple members developed lung cancer. Using whole-exome sequencing, we identified a novel germline mutation in the transmembrane domain of the human epidermal growth factor receptor 2 (HER2) gene (G660D). A novel somatic mutation (V659E) was also detected in the transmembrane domain of HER2 in one of 253 sporadic lung adenocarcinomas. Because the transmembrane domain of HER2 is considered to be responsible for the dimerization and subsequent activation of the HER family and downstream signaling pathways, we performed functional analyses of these HER2 mutants. Mutant HER2 G660D and V659E proteins were more stable than wild-type protein. Both the G660D and V659E mutants activated Akt. In addition, they activated p38, which is thought to promote cell proliferation in lung adenocarcinoma. Our findings strongly suggest that mutations in the transmembrane domain of HER2 may be oncogenic, causing hereditary and sporadic lung adenocarcinomas.

Figure 1.

Pedigree chart of a Japanese family in which multiple members developed lung cancer. The boxes and circles indicate men and women, respectively. The numbers at the bottom of each member indicate the age at the time of death or the time of the analysis. An oblique line shows deceased family members. The proband (III-4) had multiple lung adenocarcinomas (arrow). Tumor tissue, nonmalignant lung tissue, and peripheral blood samples were obtained from III-4. The proband’s mother (II-4) also had multiple lung adenocarcinomas, and tumor and nonmalignant lung tissue samples were available. The proband’s father (II-5) and sister (III-5) were both unaffected, and peripheral blood samples were obtained from these individuals. Some family members who were not considered as critical for this study were excluded from the pedigree chart to preserve confidentiality. Whole-exome sequencing was performed for individuals II-4, II-5, III-4, and III-5.

Figure 2.

DNA and amino acid sequences in the transmembrane domain of HER2. A) Direct Sanger sequencing of the proband (III-4), her affected mother (II-4), and her unaffected sister (III-5). The results indicated that G660D was a germline mutation. B) Direct sequencing of a sporadic lung adenocarcinoma with a HER2 V659E mutation. V659E was found to be of somatic origin based on the sequencing results of the peritumoral lung tissue from the same specimen. All the sequence variants were confirmed by independent polymerase chain reaction amplifications and were sequenced in both directions. C) Interspecies conservation of the transmembrane domain of HER2 (UCSC Genome Browser, http://genome.ucsc.edu, accessed September 12, 2013). The yellow highlight indicates the N-terminal glycine zipper motif Thr⁶⁵²-X₃-Ser⁶⁵⁶-X₃-Gly⁶⁶⁰, a tandem variant of a GG4-like motif of human HER2. Codons 659 and 660 in human HER2 are highly conserved among the listed vertebrate species (shown in red). X. tropicalis = Xenopus tropicalis.