Previous results showed that
GnRH signaling is altered in cells from rat luteinized ovarian
tumors (
tumor group) because it did not activate the
phospholipase C pathway, in contrast to control ovarian cells from superovulated prepubertal rats (SPO). In the present work, alternate
GnRH-induced second messengers such as
phospholipase A(2) and
phospholipase D activation, cAMP production, ERK1/2 phosphorylation, and the presence of
G proteins were evaluated to determine
GnRH mechanism of action in
tumor cells.
G proteins examined were present in both cell types.
Buserelin, a
GnRH agonist, (1, 10, and 100 ng/ml) increased
phosphatidylethanol in SPO, indicating
phospholipase D activation. Only 100 ng/ml
buserelin induced a significant response in the
tumor group.
Buserelin (100 ng/ml) increased (3)H-arachidonic
acid in
culture media in SPO, indicating
phospholipase A(2) activation; no effect was observed in the
tumor group.
Buserelin (100 and 1000 ng/ml) induced
pertussis toxin-insensitive cAMP increases in both cell types, with similar potencies. In the
tumor group,
buserelin (100 ng/ml) inhibited
human chorionic gonadotropin-induced cAMP and
progesterone; this effect was
protein kinase C (PKC) dependent (inhibited by
GF109203X, a PKC inhibitor).
Buserelin (100 and 1000 ng/ml) induced ERK1/2 phosphorylation in both cell kinds.
Buserelin-induced ERK1/2 activation was G(i/0) independent and PKC dependent. Only in the
tumor group,
buserelin-induced ERK1/2 activation was cAMP dependent (abolished by
SQ 22536, the
adenylyl cyclase inhibitor). Furthermore, dibutyryl cAMP-induced ERK1/2 activation in the
tumor group was PKC dependent (inhibited by
GF109203X). In conclusion, activation of
phospholipases in
tumor cells does not seem to mediate
GnRH effects.
GnRH signaling seems to involve
adenylyl cyclase activation, PKC stimulation, and ERK1/2 phosphorylation.