Bisleuconothine A Induces Autophagosome Formation by Interfering with AKT-mTOR Signaling Pathway

• Published in: Journal of natural products (Washington, D.C.) D.C.), 2015-07, Vol.78 (7), p.1656-1662
• Main Authors: Wong, Chin Piow, Seki, Ari, Horiguchi, Kaori, Shoji, Tomokazu, Arai, Takashi, Nugroho, Alfarius Eko, Hirasawa, Yusuke, Sato, Fumiaki, Kaneda, Toshio, Morita, Hiroshi
• Format: Article
• Language: English
• Subjects: Annexin A5 - metabolism; Apoptosis - drug effects; Apoptosis Regulatory Proteins - metabolism; Autophagy; Cell Line, Tumor; Cytostatic Agents - chemistry; Cytostatic Agents - pharmacology; Down-Regulation; Female; Humans; Indole Alkaloids - chemistry; Indole Alkaloids - isolation & purification; Indole Alkaloids - pharmacology; Malaysia; Molecular Structure; Phosphorylation; Proto-Oncogene Proteins c-akt - metabolism; TOR Serine-Threonine Kinases - drug effects; Vinblastine - pharmacology
• ISSN: 0163-3864; 1520-6025
• DOI: 10.1021/acs.jnatprod.5b00258

We have previously reported that bisleuconothine A (Bis-A), a novel bisindole alkaloid isolated from Leuconotis griffithii, showed cytostatic activity in several cell lines. In this report, the mechanism of Bis-A-induced cytostatic activity was investigated in detail using A549 cells. Bis-A did not cause apoptosis, as indicated by analysis of annexin V and propidium iodide staining. Expression of all tested apoptosis-related proteins was also unaffected by Bis-A treatment. Bis-A was found to increase LC3 lipidation in MCF7 cells as well as A549 cells, suggesting that Bis-A cytostatic activity may be due to induction of autophagy. Subsequent investigation via Western blotting and immunofluorescence staining indicated that Bis-A induced formation but prevented degradation of autophagosomes. Mechanistic studies showed that Bis-A down-regulated phosphorylation of protein kinase B (AKT) and its downstream kinase, PRAS40, which is an mTOR repressor. Moreover, phosphorylation of p70S6K, an mTOR-dependent kinase, was also down-regulated. Down-regulation of these kinases suggests that the increase in LC3 lipidation may be due to mTOR deactivation. Thus, the cytostatic activity shown by Bis-A may be attributed to its induction of autophagosome formation. The Bis-A-induced autophagosome formation was suggested to be caused by its interference with the AKT-mTOR signaling pathway.