Apoptosis of human breast cancer cells induced by hemagglutinin from Phaseolus vulgaris cv. Legumi secchi

A dimeric hemagglutinin with a relative molecular mass of 62000 was purified from seeds of Phaseolus vulgaris cultivar “Legumi secchi”. The chromatographic protocol included the use of Blue-Sepharose, Q-Sepharose, and Superdex 75. The N-terminal amino acid sequence of the hemagglutinin resembled those of other Phaseolus hemagglutinins. Its hemagglutinating activity was stable from 0 °C to 60 °C, and pH 4–11. It inhibited HIV-1 reverse transcriptase (IC50 of 17.3 μM) and suppressed the proliferation of breast cancer MCF-7 cells (IC50 of 0.2 μM). However, it was devoid of antifungal activity. The hemagglutinin-treated MCF-7 cells showed a number of changes, including cell cycle arrest in G2/M phase, phosphatidylserine externalisation and mitochondrial membrane depolarisation. The hemagglutinin-induced apoptosis through the death receptor-mediated pathway involved Fas ligands, caspase-8 activation, BID truncation, p53 release, caspase-9 activation and Lamin A/C truncation. The understanding of the apoptotic mechanism may be of value for application in tumor therapy.