Enhanced autophagy is required for survival in EGFR-independent EGFR-mutant lung adenocarcinoma cells.
Lung cancers harboring epidermal growth factor receptor (EGFR) mutations depend on constitutive activation of the kinase for survival. Although most EGFR-mutant lung cancers are sensitive to EGFR tyrosine kinase inhibitors (TKIs) and shrink in response to treatment, acquired resistance to TKI therapy is common. We demonstrate here that two EGFR-mutated lung adenocarcinoma cell lines, HCC827 and HCC4006, contain a subpopulation of cells that have undergone epithelial-to-mesenchymal transition and survive independent of activated EGFR. These EGFR-independent cancer cells, herein termed gefitinib-resistant (GR) cells, demonstrate higher levels of basal autophagy than their parental cells and thrive under hypoxic, reduced-serum conditions in vitro; this somewhat simulates the hypoxic environment common to cancerous tissues. We show that depletion of the essential autophagy gene, ATG5, by small interfering RNA (siRNA) or chloroquine, an autophagy inhibitor, markedly reduces GR cell viability under hypoxic conditions. Moreover, we show a significant elevation in caspase activity in GR cells following knockdown of ATG5. These results suggest that GR cells can evade apoptosis and survive in hostile, hypoxic environments with constant autophagic flux. We also show the presence of autophagosomes in some cancer cells from patient samples, even in untreated EGFR-mutant lung cancer tissue samples. Together, our results indicate that autophagy inhibitors alone or in combination with EGFR TKIs may be an effective approach for the treatment of EGFR-mutant lung cancers, where basal autophagy of some cancer cells is upregulated.
1] Molecular Pathology and Genetics Division, Kanagawa Cancer Center Research Institute, Yokohama, Japan [2] Laboratory for Molecular Diagnostics, Kanagawa Cancer Center Hospital, Yokohama, Japan [3] Department of Pathology, Jichi Medical University, Tochigi, Japan.
Yuji
Y
Sakuma
Shoichi
S
Matsukuma
Yoshiyasu
Y
Nakamura
Mitsuyo
M
Yoshihara
Shiro
S
Koizume
Hironobu
H
Sekiguchi
Haruhiro
H
Saito
Haruhiko
H
Nakayama
Yoichi
Y
Kameda
Tomoyuki
T
Yokose
Sachiko
S
Oguni
Toshiro
T
Niki
Yohei
Y
Miyagi
D000230:Adenocarcinoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D000077192:Adenocarcinoma of Lung; D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects; D000071187:Autophagy-Related Protein 5; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival; D019008:Drug Resistance, Neoplasm; D058750:Epithelial-Mesenchymal Transition; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D008168:Lung / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D050505:Mutant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010588:Phagosomes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference
C502778:ATG5 protein, human; D000970:Antineoplastic Agents; D000071187:Autophagy-Related Protein 5; D008869:Microtubule-Associated Proteins; D050505:Mutant Proteins; D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; C512478:EGFR protein, human; D066246:ErbB Receptors