Ca+2 Signal is Generated Only Once in the Mating Pheromone Response Pathway in Saccharomyces cerevisiae.

Abstract

ABSTRACT. The mating pheromone, α-factor, of the yeast Saccharomyces cerevisiae binds to the heterotrimeric G protein-coupled cell surface receptor of MATa cells and induces cellular responses necessary for mating. In higher eukaryotic cells, many hormones and growth factors rapidly mobilize a second messenger, Ca 2+ , by means of receptor-G protein signaling. Although striking similarities between the mechanisms of the receptor-G protein signaling in yeast and higher eukaryotes have long been known, it is still uncertain whether the pheromone rapidly mobilizes Ca 2+ necessary for early events of the pheromone response. Here we reexamine this problem using sensitive methods for detecting Ca 2+ fluxes and mobilization, and find no evidence that there is rapid Ca 2+ influx leading to a rapid increase in the cytosolic free Ca 2+ concentration. In addition, the yeast PLC1 deletion mutant lacking phosphoinositide-specific phospholipase C, a key enzyme for generating Ca 2+ signals in higher eukaryotic cells, responds normally to the pheromone. These findings suggest that the receptor-G protein signaling does not utilize Ca 2+ as a second messenger in the early stage of the pheromone response pathway. Since the receptor-G protein signaling does stimulate Ca 2+ influx after early events have finished and this stimulation is essential for late events in the pheromone response pathway {Iida et al., (1990) J. Biol. Chem., 265: 13391-13399} Ca 2+ may be used only once in the signal transduction pathway in unicellular eukaryotes such as yeast.

A Monochromatically Excitable Green–Red Dual-Fluorophore Fusion Incorporating a New Large Stokes Shift Fluorescent Protein

“…We expressed the GA-MatryoshCaMP6s sensor in budding yeast to visualize calcium spiking to the α-MF. Cytosolic calcium elevations have been implicated in α-MF signaling. , Initial results from population-scale assays using radiolabeled calcium ions ( 45 Ca 2+ ) or the chemiluminescent calcium sensor aequorin indicated the occurrence of a single calcium elevation during the yeast mating response . Consistent with a recent study that concluded that α-MF treatment strongly increased the frequency of calcium spiking, we observed a 4-fold increase in the frequency of calcium spikes in response to treatment with the α-MF .…”

Differential Phosphorylation Provides a Switch to Control How α-Arrestin Rod1 Down-regulates Mating Pheromone Response in Saccharomyces cerevisiae

“…If Rod1 is a target for Fus3 , and phosphorylation by Fus3 is also inhibitory to Rod1 -mediated stimulation of Ste2 internalization, such a circuit would provide a self-reinforcing mechanism for maintaining Ste2 at the PM and thereby more sustained pheromone signaling at least in the early phase of mating pathway activation. However, at the latter stage of pheromone response, there is a marked influx of Ca 2+ ( Ohsumi and Anraku 1985 ; Nakajima-Shimada et al 2000 ; Martin et al 2011 ) sufficient to stimulate activation of CN ( Withee et al 1997 ), which we showed previously is necessary to activate the adaptation-promoting function of Rod1 ( Alvaro et al 2014 ). As we documented here, CN activates Rod1 function by removing the phosphorylations at both the Ypk1 and Snf1 sites.…”

Specific α-Arrestins Negatively Regulate Saccharomyces cerevisiae Pheromone Response by Down-Modulating the G-Protein-Coupled Receptor Ste2

“…One hallmark of the later stages of pheromone response is a robust influx of Ca 2ϩ (133,134). This rise in intracellular Ca 2ϩ is sufficient to activate the Ca 2ϩ -dependent phosphatase calcineurin (135).…”