ARACHIDONIC-ACID AND LIPOXYGENASE PRODUCTS STIMULATE GONADOTROPIN ALPHA-SUBUNIT MESSENGER-RNA LEVELS IN PITUITARY ALPHA-T3-1 CELL-LINE - ROLE IN GONADOTROPIN-RELEASING-HORMONE ACTION
D. Benmenahem et al., ARACHIDONIC-ACID AND LIPOXYGENASE PRODUCTS STIMULATE GONADOTROPIN ALPHA-SUBUNIT MESSENGER-RNA LEVELS IN PITUITARY ALPHA-T3-1 CELL-LINE - ROLE IN GONADOTROPIN-RELEASING-HORMONE ACTION, Biochemistry, 33(43), 1994, pp. 12795-12799
The role of arachidonic acid (AA) and its lipoxygenase metabolites in
gonadotropin releasing hormone (GnRH) induced cu-subunit gene expressi
on was investigated in the transformed gonadotroph cell line alpha T3-
1. The stable analog [D-Trp(6)]GnRH (GnRHa) stimulated [H-3]AA release
from prelabeled cells after a lag of 1-2 min. Addition of AA stimulat
ed or-subunit mRNA levels in a dose-dependent manner, a significant ef
fect being detected at 5 mu M AA. Among various lipoxygenase metabolit
es of AA, only the 5-lipoxygenase products 5-hydroxyeicosatetraenoic a
cid (5-HETE) and leukotriene C-4 (LTC(4)) stimulated alpha-subunit mRN
A levels. However, while 5-HETE and LTC(4) (0.1 nM each) were active a
lready after 30 min of incubation, similar to GnRHa, AA (20 mu M) stim
ulated alpha-mRNA levels after 1 h of incubation. Addition of the phos
pholipase A(2) inhibitor 4-bromophenacyl bromide (BPB) or the selectiv
e 5-lipoxygenase inhibitor L-656,224 inhibited GnRHa elevation of alph
a-subunit mRNA by 65%, while the cyclooxygenase inhibitor indomethacin
had no effect. Addition of AA (20 mu M) or LTC(4) (0.1 nM) to normal
cultured rat pituitary cells mimicked the rapid (30 min) stimulatory e
ffect of GnRH (1 nM) upon alpha-subunit, LH beta, and FSH beta mRNA le
vels, while 5-HETE (0.1 nM) stimulated only FSH beta mRNA levels at th
is time point. Thus AA and selected 5-lipoxygenase products, in partic
ular LTC(4), participate in GnRHa-induced alpha-subunit mRNA elevation
.