Inhibition of apoptosis in HeLa cell by silkworm storage protein 1, SP1

Silkworm contains several distinct proteins that have anti-apoptotic activities in mammalian and insect cells. Although the characteristics of 30K proteins have been well investigated, those of SPs (Storage Proteins) have not been examined. In this article, an anti-apoptotic effect of SP1 was investigated in HeLa cell apoptosis. SP1, a type of insect hemocyanin protein, is a female-specific protein in silkworm and consists of high portion of methionine. Transient expression of SP1 in HeLa cells slightly increased cell viability after the treatment with staurosporine, which induced apoptosis via intrinsic mitochondrial pathway. To investigate the anti-apoptotic effect of SP1, the stable cell line expressing SP1 were screened and constructed. The anti-apoptotic effect of the cell line was assessed using trypan blue exclusion assay, microscopic analysis of nuclear fragmentation, and flow cytometry. SP1 expressing cell line showed strong antiapoptotic activity against the treatment of staurosporine but not TNFa, meaning that SP1 is a protein inhibitor of apoptosis caused by intrinsic apoptosis pathway. As the SP1 is the novel anti-apoptotic protein, the regulation of apoptosis by SP1 will offer a new strategy that can be utilized in biopharmaceutical industry when the focus is on minimization of cell death and maximization of productivity.