Does oligosaccharide-phosphatidylinositol (glycosyl-phosphatidylinositol) hydrolysis mediate prolactin signal transduction in granulosa cells?
Initial biosynthetic radiolabelling experiments with cultured granulosa cells revealed the presence of an oligosaccharide-phosphatidylinositol (glycosyl-phosphatidylinositol; (Ose)nPtdIns) structurally related to (Ose)nPtdIns-lipids isolated from other cell types. Prolactin (PRL) stimulated [3H]glucosamine-(Ose)nPtdIns turnover and the rapid generation of [3H]myristoyl-diacylglycerol in cultured follicle-stimulating hormone-(FSH)-primed granulosa cells endowed with PRL receptors. In parallel experiments performed with [3H]myo-inositol-labelled granulosa cells, treatment with PRL stimulated (Ose)nPtdIns hydrolysis in a similar manner, whereas no effect on phosphoinositide (PtdIns, PtdInsP and PtdInsP2) turnover could be observed. These results strongly suggest that the cleavage of (Ose)nPtdIns by phosphodiesterase followed by the subsequent generation of diacylglycerol and a soluble phosphoinositol-oligosaccharide (inositol-phosphoglycan; (Ose)nInsP) moiety could be part of the signal-transduction mechanism linking PRL receptors to their biological effects in granulosa cells. To test this hypothesis, we examined the effect of PRL and purified (Ose)nInsP moiety (from rat liver membranes) on granulosa cell 3 beta-hydroxysteroid dehydrogenase/delta 5-4 isomerase (3 beta-HSD) enzyme activity. Results presented show that, in FSH-primed granulosa cells, PRL (40 nM) and (Ose)nInsP (5 microM) prevented gonadotropin-stimulated 3 beta-HSD activity. Furthermore, in undifferentiated granulosa cells where PRL receptors are absent, no effect of the hormone on 3 beta-HSD activity could be observed, whereas (Ose)nInsP (1-10 microM) inhibited enzyme activity in a dose-dependent manner.
Fanjul
L F
LF
Departamento de Endocrinología Celular y Molecular, Universidad de Las Palmas de Gran Canaria, Spain.
Marrero
I
I
González
J
J
Quintana
J
J
Santana
P
P
Estévez
F
F
Mato
J M
JM
Ruiz de Galarreta
C M
CM
D000818:Animals; D002454:Cell Differentiation; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006107:Granulosa Cells / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006868:Hydrolysis; D008099:Liver / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D011375:Progesterone Reductase / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011981:Receptors, Prolactin / Q000378:metabolism; D015398:Signal Transduction; D013251:Steroid Isomerases / Q000378:metabolism
C021425:3 beta-hydroxysteroid oxidoreductase-delta(5) 3-ketosteroid isomerase; D017261:Glycosylphosphatidylinositols; D009097:Multienzyme Complexes; D011981:Receptors, Prolactin; D011388:Prolactin; D005640:Follicle Stimulating Hormone; D011375:Progesterone Reductase; D013251:Steroid Isomerases