Suppression on POLQ by PTEN Implicates a New SACC Treatment

Objectives: To detect the relationship between POLθ and PTEN in human salivary gland adenoid cystic carcinoma (SACC) and to investigate the effect of suppressing POLQ expression combined with etoposide on SACC-83 cells.
Methods: To investigate the mechanism of PTEN in SACC, siRNA targeting PTEN was transfected into SACC-83 cells and then these cells were analyzed with agilment human whole gene 4*4K expression profiling chip to find a differentially expressed gene POLQ. Detected the expression patterns of POLθ and PTEN by immunohistochemistry in SACC tissues and analyzed the relationship between POLθ and PTEN. Analyzes the relationship between POLθ and clinical prognosis by using Kaplan-Meier cumulative survival analysis. Added etoposide and suppressed POLQ expression by shRNA in SACC-83 cells, and detected the changes of γH2AX and several DNA repair related genes by western blot and real-time PCR.
Results: Compared with control group, 3131 genes were significantly differentially expressed in SACC-83 cells transfected with siPTEN, and then we found up-regulated gene POLQ. Most cases of cribriform and tubular SACCs where PTEN expressed high exhibited undetectable or low levels of POLθ. High levels of cytoplasmic and nucleus staining of POLθ were shown in solid SACCs where PTEN was nearly undetectable. POLθ was negatively correlated with PTEN. Compared with POLθ(-) patients, POLθ(+) patients had poorer outcomes. Compared with etoposide+shControl group, significantly higher level of γH2AX protein and lower levels of DNA repair related gene mRNAs (H2AFX, RAD51, MSH2, ATM, ATR, BRCA1) were found in etoposide+shPOLQ group.
Conclusions: POLQ is negatively regulated by PTEN in SACC and higher levels of POLθ mean poorer outcomes in SACC patients. Etoposide and shPOLQ have a synergistic effect on promoting DNA damage in SACC-83 cells.These results indicate combination POLQ related small molecular inhibitor with etoposide makes it possible to improve therapeutic effect on SACC