Role of mitochondrial DNA copy number alteration in non-small cell lung cancer

Background: Mitochondrial dysfunction may involve in the progression of human non-small cell lung cancers (NSCLCs). We analyzed the mitochondrial DNA (mtDNA) copy number, the expression levels of mitochondrial biogenesis-related proteins including pyruvate dehydrogenase, mitochondrial transcription factor A (TFAM) and mtDNA-encoded peptide NADH dehydrogenase subunit 1 (ND1), and the expression level of hexokinase II (HK-II) in human NSCLCs both ex vivo and in vitro. Materials and Methods: Paired cancerous and non-cancerous pathological specimens from 20 resected NSCLCs and an NSCLC cell line, the H23, were used in this study. H23 was infected by lentiviral particles to knockdown (KD) the expression of TFAM. TFAM-Null and TFAM-KD represent the control and TFAM knocked-down H23 cells, respectively. The mtDNA copy number was measured by quantitative real-time polymerase chain reaction and the protein expression levels were measured by immunohistochemical staining and Western blotting, respectively. Results: Low TFAM expression (P = 0.066) and low mtDNA copy number of NSCLCs (P = 0.009) were poor prognostic variables in NSCLC patients. Advanced T4 NSCLCs had lower TFAM expression (P = 0.021), lower expression of mtDNA-encoded ND1 polypeptide (P = 0.049), and lower mtDNA copy number (P = 0.050) than did T1 or T2/T3 NSCLCs, respectively. TFAM-KD cells expressed lower levels of TFAM protein (P < 0.005), ND1 polypeptide (P < 0.005) and mtDNA copy number (P = 0.003), but higher level of vimentin protein (P = 0.045) and higher transwell migration activity (P = 0.003) than did TFAM-Null cells. Conclusion: Mitochondrial dysfunction caused by lower levels of TFAM, mtDNA copy number, and mtDNA-encoded ND1 polypeptide may play an important role in the progression of NSCLCs.