Heat shock protein 90 as a vital signalling hub in Schistosoma mansoni: a master regulator of stem cell proliferation, development and survival

Heat shock protein 90s (HSP90s) are molecular chaperones often produced by cells in response to hostile conditions. Here, we characterized the importance of HSP90 to growth/development and survival of the blood fluke Schistosoma mansoni, focusing on life stages that parasitize the human host. Western blotting revealed striking HSP90 upregulation in developing schistosomula in vitro, and pharmacological assays revealed that the HSP90 inhibitors gedunin, 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) and 5-(2-amino-4-chloro-7-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-7H-pyrrolo[2,3-d]pyrimidin-5-yl)-2-methylpent-4-yn-2-ol (EC-144) profoundly attenuated the viability/development of skin schistosomula to lung and liver stages. In vitro liver stage, ex vivo adult male/female worms and eggs were also killed. Strikingly, 17-AAG and EC-144 blocked stem cell proliferation in the skin, lung and liver schistosomula, and the testicular lobes and ovaries of adult worms. Small interfering RNA-mediated knockdown of the cytoplasmic HSP90 alpha isoform 2 (Smp_072330) also attenuated stem cell proliferation and restricted schistosomulum growth, supporting the importance of this isoform. 17-AAG and EC-144 attenuated the phosphorylation of schistosomula Akt/protein kinase B, extracellular signal-regulated kinase and p38 mitogen-activated protein kinase, suggesting HSP90 regulates core 'system-based' signalling pathways in the parasite; glucose uptake was also reduced. Collectively, these novel findings highlight the importance of HSP90 to intra-mammalian schistosome life stages and identify HSP90 as a possible drug target to control human schistosomiasis.