Immobilization of Bioactive Growth Factors into Cubic Proteinous Microcrystals (Cypovirus Polyhedra) and Control of Cell Proliferation and Differentiation

Certain insect viruses produce stable infectious microcrystals called polyhedra which function to protect the virus after the death of infected larvae. Polyhedra form within infected cells and contain numerous virus particles embedded in a crystalline lattice of the viral protein polyhedrin. We have previously demonstrated that the Nterminal 75 amino acids of the Bombx mori cypovirus (BmCPV) turret protein can function as a polyhedrin recognition signal leading to the incorporation of foreign proteins into polyhedra. Foreign proteins tagged with the VP3 polyhedrin recognition signal were incorporated into polyhedra by co-expression with polyhedrin in insect cells. We have also reported that the N-terminal α-helix of polyhedrin directs the incorporation of foreign proteins into polyhedra. Here we show the successful occlusion of human cytokines (FGF-2, FGF-7, EGF, etc) into the BmCPV polyhedra. The polyhedra are proteinous cubic crystals of several microns in size that are insoluble in the extracellular milieu. We demonstrate that BmCPV polyhedra microcrystals that occlude extracellular signaling proteins are a novel and versatile tool that can be employed to analyze cellular behavior at the single cell level.