Epidermal Growth Factor Receptor Inhibition by Tyrphostin 51 Induces Apoptosis in Luteinized Granulosa Cells

Abstract

Growth factors may be involved in the control of ovarian cell fate and could contribute to regulation of ovarian cell apoptosis. Our objective is to test the hypothesis that, in human luteinized granulosa cells, epidermal growth factor (EGF) works through the MAPK signaling pathway and inhibition of EGF receptor by a specific tyrosine kinase inhibitor, tyrphostin 51, will inhibit the activation of MAPK and induce apoptosis. Luteinized granulosa cells from human in vitro fertilization aspirates were treated as follows: 1) vehicle (dimethylsulfoxide:ethanol), 2) EGF, 3) tyrphostin 51, and 4) tyrphostin 51 plus EGF. Blockage of EGF receptor by tyrphostin 51 reduced the MAPK activity and inhibited phosphorylation and nuclear translocation of activated MAPK. Blockage of EGF receptor also induced apoptosis as demonstrated by the activation of caspase-3, an executioner protease of the apoptotic pathway, and by an increased percentage of subdiploid apoptotic nuclei. These results support the hypothesis that in human luteinized granulosa cells, EGF works through the MAPK signaling pathway and that its inhibition by tyrphostin 51 inhibits MAPK phosphorylation and induces apoptotic nuclear changes. Our data thus provide additional information regarding regulation of apoptosis in luteinized granulosa cells.