An 85-amino-acid polypeptide from Myrmeleon bore larvae (antlions) homologous to heat shock factor binding protein 1 with antiproliferative activity against MG-63 osteosarcoma cells in vitro

Abstract

Abstract Background Venomous arthropods have substances in their venom with antiproliferative potential for neoplastic cells. Objectives To identify a polypeptide from Myrmeleon bore (antlion) with antiproliferative activity against neoplastic cells, and to elucidate the molecular mechanism of the activity. Methods We used gel filtration and ion exchange chromatography to purify a polypeptide with antiproliferative activity against MG-63 human osteosarcoma cells from a proteinaceous extract of antlion. The polypeptide was sequenced and the stability of its antiproliferative activity was tested under a range of conditions in vitro. An 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the antiproliferative activity of the polypeptide against the MG-63 osteosarcoma cells and MC3T3-E1 mouse calvarial osteoblasts, which were used as a non-neoplastic control. We used western blotting to compare the levels of expression of heat shock transcription factor 1 (HSF1), heat shock protein 90 (HSP90), cyclin-dependent kinase 4 (CDK4), and protein kinase B alpha (ATK1) in MG-63 osteosarcoma cells and their mouse homologs in MC3T3-E1 osteoblasts after their treatment with the antlion antiproliferative polypeptide (ALAPP). Results The 85-amino-acid ALAPP has a 56% sequence identity with the human heat shock factor binding protein 1 (HSBP1). The antiproliferative activity of the polypeptide is relatively insensitive to temperature, pH, and metal ions. ALAPP has a strong concentration-dependent antiproliferative activity against MG-63 osteosarcoma cells compared with its effect on MC3T3-E1 osteoblasts. ALAPP significantly upregulates the expression of HSF1 in MC3T3-EL osteoblasts, but not in MG-63 osteosarcoma. ALAPP significantly downregulated the expression of HSP90, CDK4, and AKT1 expression in MG-63 osteosarcoma, but not in the osteoblasts. Conclusions ALAPP has significant antiproliferative activity against MG-63 osteosarcoma cells, but not nonneoplastic MC3T3-E1 osteoblasts. We speculate that non-neoplastic cells may evade the antiproliferative effect of ALAPP by upregulating HSF1 to maintain their HSP90, CDK4, and AKT1 expression at a relatively constant level.