engleski

Phospholipase C isoforms have different subnuclear localization and mechanisms of activation

Phospholipase C (PLC) was purified from the membrane-depleted rat liver nuclei. About 60% of the total PLC-activity corresponded to beta1b-isoform, 30% to PLC-gamma1 and less then 10% to PLC-delta1. PLC-beta1b and gamma1 were found in the nuclear matrix, while PLC-delta1 was detected in the chromatin. Two peaks of increase in the total PLC-activity were detected occurring at 6 h and 20 h after partial hepatectomy. An early increase in PLC-beta1b-activity in the nuclear matrix was associated with serine phosphorylation of the enzyme, while the later increase paralleled the increase in the amount of protein. The increase in the PLC-gamma1-activity measured at 6 h and 20 h after partial hepatectomy were associated with tyrosine phosphorylation of the enzyme. The activity of PLC-delta1 and the amount of the protein found in the chromatin was increased only at 20 h after partial hepatectomy. Furthermore, when activity of nuclear PLC was investigated in HL-60 cells blocked at G2/M phase by the addition of nocodazole, and released into medium as synchronously progressing cells, two peaks in the nuclear PLC activities were detected ; an early peak reached a maximum at 1 h after release from the nocodazole block, and a second increase was detected at 8.5 h after the release. Immunoprecipitation studies indicated that the increase in the activity was due to the activation of the beta1b-isoform. An increase in the serine-phosphorylation of beta1b-isoform was detected in the nuclei isolated at 1 and 8.5 h after the block, and the presence of MEK-inhibitor PD98059 completely inhibited both the serine phosphorylation and the increase in the nuclear PLC activities in vitro. The presence of PLC inhibitor prevented the progression of HL-60 cells through the G1 into S phase of cell cycle. These results show that increase in the nuclear PLC activity, due to a phosphorylation of beta1b-isoform on serine, occur at the G2/M and late G1 phase and is necessary for the progression of the cells through the cell cycle.

phospholipase C; nuclei; rat liver; HL-60 cells; activation

nije evidentirano