Identification of the mitochondrial protein ADCK2 as a therapeutic oncotarget of NSCLC.

The aarF domain containing kinase 2 (ADCK2) is a mitochondria-locating protein, important for fatty acid metabolism and coenzyme Q biosynthesis. The bioinformatics results show that elevated ADCK2 transcripts in NSCLC correlate with poor overall survival and poor anti-PD-1/PD-L1 therapy response. ADCK2 is overexpressed in local human NSCLC tissues and various primary and established NSCLC cells. In NSCLC cells, ADCK2 shRNA or CRISPR/Cas9 knockout remarkably suppressed cell viability, proliferation, cell cycle progression, cell mobility, and provoked cell apoptosis. Moreover, ADCK2 depletion disrupted mitochondrial functions in NSCLC cells, causing cytochrome C release, mitochondrial depolarization, DNA damage and ATP reduction. Contrarily, ectopic ADCK2 overexpression promoted NSCLC cell growth. Further studies revealed that ADCK2 depletion inactivated Akt-mTOR signaling in primary NSCLC cells. NSCLC xenograft growth in nude mice was significantly hindered after ADCK2 silencing or knockout. ADCK2 depletion, apoptosis induction and oxidative injury as well as ATP reduction and Akt-mTOR inactivation were detected in ADCK2-silenced or ADCK2-knockout NSCLC xenograft tissues. Together overexpressed ADCK2 is important for the growth of NSCLC cells, representing an important therapeutic molecular oncotarget.

Radiation alters PD-L1/NKG2D ligand levels in lung cancer cells and leads to immune escape from NK cell cytotoxicity via IL-6-MEK/Erk signaling pathway.

We investigated whether radiation influences the susceptibility of non-small cell lung cancer (NSCLC) cells to NK cell mediated cytotoxicity. We found radiation treatment increased expression of programmed cell death ligand 1 (PD-L1), but decreased NK group 2, member D (NKG2D) ligand expressions in A549 and H157 NSCLC cells. Both types of changes would have protected tumor cells from the cytotoxic action of NK cells. Consistently, we detected similar alteration in these molecules in radioresistant A549R26-1 and H157R24-1 subline cells. Higher PD-L1 level was also observed in tumors of A549R26-1 cell-derived xenografts than tumors of parental A549 (A549P) cell-derived xenografts. Accordingly, we found radioresistant cells were more resistant to the cytotoxic action of NK cells than parental cells, and such resistance was decreased when neutralizing antibody (Ab) of PD-L1 was added to the radioresistant cell/NK cell co-cultures. In mechanism studies, we found that IL-6-MEK/Erk signaling contributed most significantly to the up-regulation of PD-L1/down-regulation of NKG2D ligands in radioresistant cells. The addition of the MEK/Erk inhibitor increased the susceptibility of A549R26-1 and H157R24-1 cells to NK-cell cytotoxicity while no significant effect was observed in parental cells. Moreover, we detected enhanced NK-cell cytotoxicity to radioresistant cells when PD-L1 Ab and MEK/Erk inhibitor were added together to co-cultures of tumor/NK cells compared to when PD-L1 Ab was used alone. We suggest that combined use of PD-L1 Ab and MEK/Erk inhibitor may offer better therapeutic benefits than PD-L1 Ab alone to treat NSCLC patients who are receiving radiotherapy or who are at the radioresistant stage.