Background and purpose: Drug resistance is a major cause of failure in lung cancer chemotherapy. This study aimed to investigate the effect of YAP on doxorubicin resistance in lung cancer and its underlying mechanism. Methods: Doxorubicin resistant lung cancer cell clones were established from parental sensitive cancer PC9 cell line via in vitro induction

and the expression of YAP was analyzed. YAP was down-regulated via shRNA to different levels. MTS assay was employed to determine cell proliferation and drug

sensitivity. Flow cytometry was used to determine cell cycle distribution

apoptosis and uptake of Rh-123. Western blot and quantitative real-time polymerase chain reaction (QRTPCR) assay were used to determine the expression of ABCB1

ABCC1

p53

Runx2

ITGB2 and ErbB4. The phosphorylation of serine/threonine kinase (AKT) was determined as well. Results: Doxorubicin resistant PC9/Adr cell clone was obtained with over-expressed YAP. Expression of YAP in PC9/Adr cells was down-regulated to different levels via shRNA. After YAP silencing

cell proliferation was reduced

while sensitivity to doxorubicin was increased. The cell cycle was significantly halted by G

0

/G

1

phase. Doxorubicin induced-apoptotic rate and cellular uptake of Rh-123 were increased

with positive correlation to YAP silencing level. Western blot and QRT-PCR results showed that after YAP silencing

ABCB1

ABCC1

Runx2

ITGB2

and ErbB4 proteins were down-regulated

while the expression of p53 was up-regulated. Phosphorylation of AKT was inhibited as well. Conclusion: Over-expression of YAP is involved in doxorubicin resistance in PC9/Adr cell line. Silencing of YAP could restore doxorubicin sensitivity. The mechanism involves regulation of drug resistance-related genes and promotion of apoptosis.