Previous studies demonstrated that nuclear EGFR is associated with malignancy and resistance to tyrosine kinase inhibitor (TKI). To decipher the cellular compartmentalized functions and underlying mechanism of EGFR, we generated EGFR mutants at nuclear translocation signal (NLS) and nuclear export signal (NES). The results showed that EGFR NLS mutant with decreased nuclear translocation sensitized the cancer cells to TKI and impaired invasiveness and stemness of the cancer cells. In contrast, EGFR NES mutant with increased nuclear accumulation promoted aggressiveness of the cancer cells including TKI resistance. Next, we generated genetically engineered mouse model (GEMM) to validate the resulting phenotypes of the EGFR mutants. To this end, CRISPR-Cas9-mediated genome editing approach was used for generating EGFR mutant knock-in mouse, which harbors an internalization-deficient mutation (EGFRLL/AA), pro-nuclear (NES) mutation (EGFRL749P(S)) and the dual mutations. Upon EGF stimulation nuclear EGFR (nEGFR) accumulation in the hepatocytes from EGFRL749P heterozygous mice was increased. Conversely, a significant reduction of nEGFR was observed in the hepatocyte from EGFTRLL/AA homozygous mice. We found that germline expression of EGFRL749P(S) gave rise to deficiency in breeding. However, EGFRLL/AA mutant mice displayed no gross abnormal even in homozygous offspring, suggesting that depletion of nEGFR has no significant phenotype. We failed to generate homozygotes of EGFR NES mutant mice due to embryonic lethality. Of note, the female and male founders and F1 EGFRL798P(S) mice developed tumors with huge spleen. The IHC staining results indicated that the infiltrating lymphocytes in liver, stomach and kidney were B cells. The latency of the B cell lymphomagenesis was from 17 to 23 months, and tumor incidence of F1 offspring of EGFRL749P(S) knock-in mice was 10 of 15 (66.7%). These findings indicated that single allele mutation in EGFR NES domain is capable of driving lymphomagenesis, suggesting that the EGFR NES mutant possesses a strong oncogenic activity. Surprisingly, by searching database of EGFR mutation in human tumors (Cosmic database https://cancer.sanger.ac.uk/cosmic ), we noticed that among the somatic mutations in EGFR gene the gene amplification represents only small part of the gene alternations in human cancers, and EGFR L747P and L747S mutation occur in the lung cancer patients with intrinsic TKI resistance. In addition, the majority of human B lymphocyte originated tumors harboring EGFR NES mutation are also heterozygotes. Cosmic database shows that somatic mutations at the EGFR NES region occur in the patients with plasma cell lymphoma. Taken together, our findings suggest that nEGFR contributes to malignant potential of the tumors and EGFR with NES mutation is a tumor driver.
Citation Format: Lei Nie, Junwei Hou, Yu-Yi Chu, Ying-Nai Wnag, Li-Chuan Chan, Longfei Huo, Paul Chiao, Shao-Chun Wang, Mien-Chie Hung, Michael Wang. Compartmentalized functions of epidermal growth factor receptor (EGFR) in tumorigenesis and malignant phenotypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 120.