Background: Cassane-type diterpenoids are widely distributed in the medical plants of genus Caesalpinia.
To date, plenty of cassane diterpenoids have been isolated from the genus Caesalpinia, and some of
them were documented to exhibit multiple biological activities. However, the effects of these compounds on
autophagy have never been reported.
Objective: To investigate the effects and mechanisms of the cassane diterpenoids including Phanginin R (PR) on
autophagy in Non-Small Cell Lung Cancer (NSCLC) A549 cells.
Methods: Western blot analysis and immunofluorescence assay were performed to investigate the effects of the
compounds on autophagic flux in A549 cells. The pathway inhibitor and siRNA interference were used to investigate
the mechanism of PR. MTT assay was performed to detect cell viability.
Results: PR treatment upregulated the expression of phosphatidylethanolamine-modified microtubule-associated
protein Light-Chain 3 (LC3-II) in A549 cells. Immunofluorescence assay showed that PR treatment increased
the production of red-fluorescent puncta in mRFP-GFP-LC3 plasmid-transfected cells, indicating PR promoted
autophagic flux in A549 cells. PR treatment activated the c-Jun N-terminal Kinase (JNK) signaling pathway
while it did not affect the classical Akt/mammalian Target of Rapamycin (mTOR) pathway. Pretreatment with
the JNK inhibitor SP600125 or siRNA targeting JNK or c-Jun suppressed PR-induced autophagy. In addition,
cotreatment with the autophagy inhibitor Chloroquine (CQ) or inhibition of the JNK/c-Jun signaling pathway
increased PR-induced cytotoxicity.
Conclusion: PR induced cytoprotective autophagy in NSCLC A549 cells via the JNK/c-Jun signaling pathway,
and autophagy inhibition could further improve the anti-cancer potential of PR.