PROTEIN-KINASE-C-MEDIATED INTERPHASE LAMIN-B PHOSPHORYLATION AND SOLUBILIZATION

Disassembly of the sperm nuclear envelope at fertilization is one of t he earliest events in the development of the male pronucleus. We repor t that nuclear lamina disassembly in interphase sea urchin egg cytosol is a result of lamin B phosphorylation mediated by protein kinase C ( PKC). Lamin B of permeabilized sea urchin sperm nuclei incubated in fe rtilized egg G(1) phase cytosolic extract is phosphorylated within 1 m in of incubation and solubilized prior to sperm chromatin decondensati on. Phosphorylation is Ca2+-dependent. It is reversibly inhibited by t he PKC-specific inhibitor chelerythrine, a PKC pseudosubstrate inhibit or peptide, and a PKC substrate peptide, but not by inhibitors of PKA, p34(cdc2) or calmodulin kinase II. Phosphorylation is inhibited by im munodepletion of cytosolic PKC and restored by addition of purified ra t brain PKC. Sperm lamin B is a substrate for rat brain PKC in vitro, resulting in lamin B solubilization. Two-dimensional phosphopeptide ma ps of lamin B phosphorylated by the cytosolic kinase and by purified r at PKC are virtually identical. These data suggest that PKC is the maj or kinase required for interphase disassembly of the sperm lamina.