HAMLET: Functional Properties and Therapeutic Potential

James Ho CS; Anna Rydström; Maria Trulsson; Johannes Bålfors; Petter Storm; Manoj Puthia; Aftab Nadeem; Catharina Svanborg


Future Oncol. 2012;8(10):1301-1313. 

In This Article

Apoptosis & Macroautophagy

HAMLET-treated cells show signs of apoptosis such as cell shrinkage, nuclear condensation, caspase activation and DNA fragmentation.[9] However, inhibition of apoptosis by the pan-caspase inhibitor zVAD-FMK does not prevent cells from dying and overexpression of the antiapoptotic BCL-2 and BCL-XL proteins does not change the sensitivity of tumor cells towards HAMLET. HAMLET-induced cell death is also p53-independent.[54]

BAMLET has been shown to induce caspase activation in several tumor cell lines.[55] In addition, BAMLET colocalizes with lysosomes in tumor cells and causes lysosomal membrane permeabilization followed by leakage of cathepsin L from the lysosome into the cytoplasm.[55]

In parallel with apoptosis, HAMLET triggers macroautophagy.[56] Extreme responses may cause so-called autophagic/type II cell death.[57–59] Evidence of macroautophagy was first obtained by electron microscopy, when double membrane vesicles were observed after HAMLET treatment. Subsequently, other changes typical of macroautophagy were also observed, including LC3 translocation and accumulation.[56] Inhibition by Beclin 1 and Atg5 siRNAs reduced HAMLET-induced macroautophagy and showed marginal effects on cell death, suggesting that autophagy is one of several responses occurring in cells that die in response to HAMLET.