PI3K/AKT/mTOR Pathway Regulate CA916798: Research Of How CA916798Induces Lung Cancer Cisplatin Resistance

Background：Resistant to chemotherapy is a major cause of treating failure in patients with lungcancer. Cisplatin is a first-line chemotherapy medicine for the lung cancer treatment, itsmain function is through inhibition of DNA synthesis to induce tumor cell apoptosis.Resistance to cisplatin is seriously affecting the clinical efficacy of lung cancer, and its mainmechanism is not elucidated clearly.Recent studies showed that: PI3K/AKT pathway play an important role in cisplatinresistance. AKT1overexpression causes cisplatin resistance of ordinary lung cancer cells,and cisplatin resistance can be reversed by AKT1inhibition in multi-drug resistance(MDR) lung adenocarcinoma cell (A549/CDDP). A further study found that AKT1induced lung cancer cells to cisplatin resistance through mTOR-P70S6K1signalingpathway.CA916798is a new drug resistance-related gene found by SSH technology in humanMDR lung adenocarcinoma cell line SPC-A-1/CDDP. CA916798overexpression inducedcisplatin-sensitive small cell lung cancer cell lines H446resistant to cisplatin. Similar toAKT1, CA916798may also induce chemotherapy drug resistance though inhibition ofapoptosis pathway. Thus we speculate that there may be some interaction betweenCA916798and AKT1pathway in vivo. Studying their relationship would undoubtedly helpus understanding how CA916798induces cisplatin resistance of lung cancer.Bioinformatics forecast showed CA916798protein may contain a sulfuric acid tyrosinesites, three protein kinase C phosphorylation sites and three casein kinase Ⅱ phosphor-ylation sites, suggesting that this protein maybe associated with signal transduction. In thePI3K-AKT-mTOR-P70S6K1pathway, in addition to PI3K, the other three components areall serine and threonine kinases, which can phosphorylate substrates on the serine orthreonine residue sites. Thus we speculated that resistance-related genes CA916798maybe substrates or targets of AKT signaling pathway. However, we know little about CA916798for this protein had no homology with other known proteins. Therefore, it could not beexcluded that CA916798may be upstream signal of PI3K/AKT pathway. On the basis ofthis speculation, we attempts to use human lung adenocarcinoma A549cells to observeeffect of inhibiting CA916798expression to PI3K/AKT pathway, while observing theinfluence of inhibition or activation of PI3K/AKT pathway on CA916798, preliminarilyelucidates the relationship between PI3K/AKT pathway and CA916798through bothpositive and negative aspects.Objective：To explore interaction between CA916798and PI3K/AKT pathway, which mayprovide basis for further study of how CA916798induces lung cancer cisplatin resistance.Method：(1)CA916798, P-AKT1, P-mTOR expression were compared between chemotherapy-resistant and chemotherapy-sensitive tumor pathological specimens.(2)Interaction and joint distribution of CA916798and P-AKT1in A549andA549/CDDP cell lines were observed by co-immunoprecipitation and immuno-histochemistry dual fluorescence, preliminary to explore the role of the interaction whichbetween CA916798and AKT pathway in lung cancer cisplatin-resistance.(3)Sustained activation or inhibition of AKT1were carried out in A549andA549/CDDP cell lines, and then mRNA and protein expression (including total protein andphosphorylated proteins)of CA916798AKT1and mTOR were observed.(4)we inhibited PI3K CA916798mTORC1/2expression respectively, and thendetect mRNA and protein expression changes of CA916798AKT1and mTOR.Results：(1)CA916798P-AKT P-mTOR expression were all significantly higher in chemo-therapy-resistance lung cancer specimens than sensitive patients respectively. Theirchanging tendency were similar.(2)CA916798interacted with P-AKT1in vivo, and the interaction were moreremarkable in cisplatin resistant pulmonary adenocarcinoma A549/CDDP cell line than itsparental A549cell line.(3)Inhibition of P-AKT1(AKT1-K179MAKT1-siRNAand LY294002)dramaticly reduced CA916798expression in both A549and A549/CDDP cell lines, while activation ofP-AKT1increase CA916798expression in both A549and A549/CDDP cell linesrespectively.(4)MTORC1inhibition through Rapamycin reduced CA916798expression in A549and A549/CDDP cell lines, while mTORC2inhibition by Rictor-siRNA also suppressedCA916798expression as well.(5)CA916798inhibition showed no obvious affection on expression of mainmembers of PI3K/AKT pathway in both A549and A549/CDDP cell lines.Conclusion：(1)CA916798located in downstream of PI3K/AKT/mTOR pathway.(2)PI3K/AKT/mTOR pathway may regulate CA916798in transcriptional level, andthat maybe important mechanism of how CA916798induces cisplatin resistance in lungcancer.