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-t