RESUMO
The anticancer therapeutic effects of usnic acid (UA), a lichen secondary metabolite, have been demonstrated in vitro and in vivo. However, the mechanism underlying the anticancer effect of UA remains to be clarified. In this study, the target protein of UA was identified using a UA-linker-Affi-Gel molecule, which showed that UA binds to the 14-3-3 protein. UA binds to 14-3-3, causing the degradation of proteasomal and autophagosomal proteins. The interaction of UA with 14-3-3 isoforms modulated cell invasion, cell cycle progression, aerobic glycolysis, mitochondrial biogenesis, and the Akt/mTOR, JNK, STAT3, NF-κB, and AP-1 signaling pathways in colorectal cancer. A peptide inhibitor of 14-3-3 blocked or regressed the activity of UA and inhibited its effects. The results suggest that UA binds to 14-3-3 isoforms and suppresses cancer progression by affecting 14-3-3 targets and phosphorylated proteins.
RESUMO
Lichens produce various unique chemicals that are used in the pharmaceutical industry. To screen for novel lichen secondary metabolites that inhibit the stemness potential of colorectal cancer cells, we tested acetone extracts of 11 lichen samples collected in Chile. Tumidulin, isolated from Niebla sp., reduced spheroid formation in CSC221, DLD1, and HT29 cells. In addition, mRNA expressions and protein levels of cancer stem markers aldehyde dehydrogenase-1 (ALDH1), cluster of differentiation 133 (CD133), CD44, Lgr5, and Musashi-1 were reduced after tumidulin treatment. Tumidulin decreased the transcriptional activity of the glioma-associated oncogene homolog zinc finger protein (Gli) promoter in reporter assays, and western blotting confirmed decreased Gli1, Gli2, and Smoothened (SMO) protein levels. Moreover, the tumidulin activity was not observed in the presence of Gli and SMO inhibitors. Together, these results demonstrate for the first time that tumidulin is a potent inhibitor of colorectal cancer cell stemness.