Differential in vitro degradation of particular Fos family members expressed by kainic acid in nuclear and cytosolic fractions of murine hippocampus

Mice were injected with kainic acid (KA) at a convulsive dose, followed by homogenization of the hippocampus in the presence of different protease and phosphatase inhibitors, and subsequent preparation of nuclear and cytosoli c fractions. An intraperitoneal injection of KA resulted in marked expressi on of particular Fos family members, including c-Fos, Fra-2, and Fos-B, but not Fra-1 proteins, in both fractions 2 to 18 h after administration. Thes e fractions were individually incubated at 30 degreesC for 1 to 18 h for de termination of in vitro degradation. Similarly rapid degradation was seen w ith c-Fos protein between nuclear fractions obtained 2 and 18 h after admin istration, while no significant degradation was found for c-Fos protein in cytosolic fractions obtained 2 h after administration during incubation. By contrast, in vitro incubation led to rapid degradation of c-Fos protein in cytosolic fractions obtained 18 h after administration. Degradation profil es were peculiar to each member protein in nuclear and cytosolic fractions obtained 2 and 18 h after administration. Dialysis prevented degradation of c-Fos protein in nuclear fractions without markedly affecting that in cyto solic fractions in a manner independent of the time after administration. T he addition of inhibitors for phosphatases, but not for proteases, accelera ted the degradation of c-Fos protein in nuclear fractions previously dialyz ed. These results suggest that in vivo KA signals may modulate heterologous machineries responsible for breakdown of each Fos family member in a uniqu e manner in nuclear fractions, rather than cytosolic fractions, of murine h ippocampus. (C) 2001 Wiley-Liss, Inc.