Role of inositol polyphosphates in programed cell death in Dictyostelium discoideum and its developmental life cycle.

Programed cell death or apoptosis is a key developmental process that maintains tissue homeostasis in multicellular organisms. Inositol polyphosphates (InsPs) are key signaling molecules known to regulate a variety of cellular processes including apoptosis in such organisms. The signaling role of InsPs in unicellular organisms such as Dictyostelium discoideum (D. discoideum) is not well understood. We investigated whether InsPs also play any role in apoptosis in D. discoideum and whether InsPs-mediated apoptosis follows a mechanism similar to that present in higher multicellular eukaryotes. We measured known apoptotic markers in response to exogenously administered InsP6, the major InsPs in the cell. We found that InsP6 was able to cause cell death in D. discoideum cell culture in a dose- and time-dependent manner as determined by cytotoxicity assays. Fluorescence staining with acridine orange/ethidium bromide and flow cytometry results confirmed that the cell death in D. discoideum by InsP6 was due to apoptotic changes. Poly(ADP-ribose) expression, a known apoptotic marker used in D. discoideum, was also increased following InsP6 treatment suggesting a role for InsP6-mediated apoptosis in this organism. InsP6-mediated cell death was accompanied by production of reactive oxygen species and a decrease in mitochondrial membrane potential. Additionally, we studied the effects of InsP6 on the developmental life cycle of D. discoideum, the process likely affected by apoptosis. In conclusion, our studies provide evidence that InsP6-mediated cell death process is conserved in D. discoideum and plays an important signaling role in its developmental life cycle.