Antimicrobial peptaibols, novel suppressors of tumor cells, targeted calcium-mediated apoptosis and autophagy in human hepatocellular carcinoma cells

Abstract

BackgroundHepatocellular carcinoma (HCC) is one of the most common cancers in the world which is highly chemoresistant to currently available chemotherapeutic agents. Thus, novel therapeutic targets are needed to be sought for the successful treatment of HCC. Peptaibols, a family of peptides synthesized non-ribosomally by the Trichoderma species and other fungi, exhibit antibiotic activities against bacteria and fungi. Few studies recently showed that peptaibols exerted cytotoxicity toward human lung epithelial and breast carcinoma cells. However, the mechanism involved in peptaibol-induced cell death remains poorly understood.ResultsHere, we showed that Trichokonin VI (TK VI), a peptaibol from Trichoderma pseudokoningii SMF2, induced growth inhibition of HCC cells in a dose-dependent manner. It did not obviously impair the viability of normal liver cells at lower concentration. Moreover, the suppression of cell viability resulted from the programmed cell death (PCD) with characteristics of apoptosis and autophagy. An influx of Ca2+ triggered the activation of μ-calpain and proceeded to the translocation of Bax to mitochondria and subsequent promotion of apoptosis. On the other hand, typically morphological characteristics consistent with autophagy were also observed by punctate distribution of MDC staining and the induction of LC3-II, including extensive autophagic vacuolization and enclosure of cell organelles by these autophagosomes. More significantly, specific depletion of Bak expression by small RNA interfering (siRNA) could partly attenuate TK VI-induced autophagy. However, siRNA against Bax led to increased autophagy.ConclusionTaken together, these findings showed for the first time that peptaibols were novel regulators involved in both apoptosis and autophagy, suggesting that the class of peptaibols might serve as potential suppressors of tumor cells.

Unique amalgamation of primary and secondary structural elements transform peptaibols into potent bioactive cell-penetrating peptides

“…Alamethicin, an archetypical peptaibol, was eightfold less potent than 1 against PANC-1 cells (SI Appendix, Table S19). This agrees with widely reported cytotoxic properties described for most known peptaibols (18)(19)(20)(21)(22)(23)(24)(25). To provide an overall better understanding of the antiproliferative and cytotoxic properties of 1, the 10 helix is shown that was generated with Φ-and Ψ-angles of −49°and −29°for poly-Ala dodecamer using the PepMake 1.2 server at pepmake.wishartlab.com/.…”

“…T2, the fungus was grown in several types of broth media. Growth of the fungus in a modified potato dextrose broth (PDB) resulted in the generation of numerous new and known members of the malettinin family of polyketides [malettinins A (27), B (28), and F-H (16)(17)(18)(19)(20), respectively] ( Fig. 2A).…”

“…The peptaibols have been intensively studied because of their abilities to form pores in the outer membranes of cells; these pore-forming capabilities result in most compounds in this class exhibiting nonspecific cytotoxic properties toward bacterial, fungal, and mammalian cells (15,17). The effects of peptaibols on mammalian cells tend to be relatively modest, causing the loss of cell viability at concentrations in the mid-to-high micromolar range (18)(19)(20)(21)(22)(23)(24)(25). With many hundreds of peptaibols reported, finding new peptaibol analogs that possess an alternative mode of biological activity would be an impracticable prospect if one relied solely on either chemically driven or genome-based approaches to identify candidate molecules.…”

“…The mechanism of cell cytotoxicity induced by the peptaibols has been extensively studied and it has been consistently demonstrated that their abilities to induce cell death are related to their pore-forming capabilities (18)(19)(20)(21)(22)(23)(24)(25). Considering the increased potencies and unique structural features of the gichigamins, we first investigated whether these peptaibols incorporate into membranes to form pores.…”

Anti-tumoral action of cannabinoids on hepatocellular carcinoma: role of AMPK-dependent activation of autophagy

“…17 Although functional autophagy acts as a metabolic stress buffer, many lines of evidence support a role for autophagy in antagonizing cell survival and in promoting cell death and apoptosis. [18][19][20] Autophagy has an important role in cancer, and inhibition of this cellular process has been proposed to contribute to HCC progression, 21,22 and, therefore, it is a potentially very important target for liver cancer prevention and treatment.…”