PtdIns(4,5)P2 and phospholipase C-independent Ins(1,4,5)P3 signals induced by a nitrogen source in nitrogen-starved yeast cells

Abstract

Addition of ammonium sulphate to nitrogen-depleted yeast cells resulted in a transient increase in Ins(1,4,5)P3, with a maximum concentration reached after 7–8min, as determined by radioligand assay and confirmed by chromatography. Surprisingly, the transient increase in Ins(1,4,5)P3 did not trigger an increase in the concentration of intracellular calcium, as determined in vivo using the aequorin method. Similar Ins(1,4,5)P3 signals were also observed in wild-type cells treated with the phospholipase C inhibitor 3-nitrocoumarin and in cells deleted for the only phospholipase C-encoding gene in yeast, PLC1. This showed clearly that Ins(1,4,5)P3 was not generated by phospholipase C-dependent cleavage of PtdIns(4,5)P2. Apart from a transient increase in Ins(1,4,5)P3, we observed a transient increase in PtdIns(4,5)P2 after the addition of a nitrogen source to nitrogen-starved glucose-repressed cells. Inhibition by wortmannin of the phosphatidylinositol 4-kinase, Stt4, which is involved in PtdIns(4,5)P2 formation, did not affect the Ins(1,4,5)P3 signal, but significantly delayed the PtdIns(4,5)P2 signal. Moreover, wortmannin addition inhibited the nitrogen-induced activation of trehalase and the subsequent mobilization of trehalose, suggesting a role for PtdIns(4,5)P2 in nitrogen activation of the fermentable-growth-medium-induced signalling pathway.

FgTep1p is linked to the phosphatidylinositol‐3 kinase signalling pathway and plays a role in the virulence of Fusarium graminearum on wheat

“…The generation of PtdIns(3,4,5)P3 at the plasma membrane is critical for the regulation of mammalian cell proliferation and survival (Cantley, 2002). However, S. cerevisiae and plant cells do not contain detectable amounts of PtdIns(3,4,5)P3 (Bergsma et al ., 2001; Dove et al ., 1997). Therefore, the physiological substrates for TEP1 in yeast and plant cells could be different from those in mammalian cells.…”

Phosphoinositides in yeast: genetically tractable signalling

“…Pro¢lin can bind in a mutually exclusive way to either globular actin, thereby promoting polymerization, or to PtdIns(4,5)P 2 . Concomitant with such a role, a transient increase in PtdIns(4,5)P 2 levels has been observed during nutrient-induced signal transduction [23]. Although, besides pro¢lin, other factors certainly contribute to the organization of the actin cytoskeleton, these experiments indicate a function for PtdIns(4,5)P 2 in cytoskeletal organization.…”

Ethanol-induced pseudohyphal transition in the cells of Candida tropicalis: participation of phosphoinositide signal transduction

“…Following the classical pathway, mainly established in mammalian cells, IP 3 is generated by cleavage of PIP 2 into diacylglycerol and IP 3 in a reaction catalysed by phospholipase C (Nishizuka, 1988). Recently, however, an alternative mechanism for the generation of IP 3 in eukaryotic cells was discovered in Dictyostelium (Van Dijken et al ., 1997) and S. cerevisiae (Bergsma et al ., 2001). When nitrogen becomes the limiting factor for yeast growth and division, the re‐addition of the lacking nutrients to the growth medium causes yeast cells to activate several signal‐transduction pathways to quickly adapt to the improved conditions.…”

“…This increase is due to the mechanism involving dephosphorylation of inositol (1,3,4,5,6)P 5 , inositol (1,3,4,5)P 4 and inositol (1,4,5,6) P 4 to IP 3 , by an inositol polyphosphatase (Van Dijken et al ., 1997). However, in this study, the nitrogen source was sufficient and an increase in IP 3 levels lasted for 2 to 3 h instead of 5 to 15 min, which had been reported in the case of activating FGM pathway (Bergsma et al ., 2001). In order to examine the possibility of the involvement of the FGM pathway in C. tropicalis pseudohyphal transition, further analyses, including investigations into inositol tetrakisphosphate and inositol pentakisphosphate levels, will be needed.…”