Probing the mechanism of FET3 repression by Izh2p overexpression

Abstract

We previously reported a role for the IZH2 gene product in metal ion metabolism. Subsequently, Izh2p was also identified as a member of the PAQR family of receptors and, more specifically, as the receptor for the plant protein osmotin. In this report, we investigate the effect of Izh2p on iron homeostasis. We show that overproduction of Izh2p prevents the iron-dependent induction of the Fet3p component of the high-affinity iron-uptake system and is deleterious for growth in iron-limited medium. We demonstrate that the effect of Izh2p requires cAMP-dependent kinase and AMP-dependent kinase and is not mediated by general inhibition of the Aft1p iron-responsive transcriptional activator. We also show that Izh2p-overproduction negatively regulates Nrg1p/Nrg2p- and Msn2p/Msn4p-dependent reporters. Furthermore, we show that the Nrg1p/Nrg2p and Msn2p/Msn4p pairs are epistatic to each other with respect to their effects on FET3 expression. Finally, we show that the mechanism by which PAQR receptors activate signal transduction pathways is likely to be conserved from yeast to humans.

Sphingolipids Function as Downstream Effectors of a Fungal PAQR

“…Hence, we have already demonstrated the efficacy of this system for testing models of signal transduction and identifying novel players in the pathway. We also demonstrated that human PAQRs, when expressed in yeast, repress FET3 in response to activation by their respective agonists (Kupchak et al, 2007;Smith et al, 2008), thus demonstrating that the mechanism of signal transduction may be conserved in the PAQR family.…”

“…The ypc1⌬ydc1⌬ double mutant (MAT␣;ade2;his3;leu2;trp1;ura3;can1;ypc1::LEU2;ydc1::TRP1) and the isogenic W303-1A wild type (MAT␣;ade2;his3;leu2;trp1;ura3;can1) background strains were a gift from Dr. Howard Riezman at the University Basel, Switzerland (Schorling et al, 2001). FET3-lacZ was used as a FET3 promoter/lacZ reporter plasmid and was described previously (Kupchak et al, 2007). IZH2 and YPC1 were cloned into pRS316-GAL1 via gap repair as described previously (Lyons et al, 2004).…”

“…In addition, we determined that cAMP-dependent protein kinase (PKA) was essential for these effects (Kupchak et al, 2007). Most importantly, however, we demonstrated that the PAQR-dependent signaling pathway in yeast does not involve G␣ proteins, indicating that PAQRs are not likely to be GPCRs (Smith et al, 2008).…”

“…While attempting to elucidate the physiological role of Izh2p, we discovered that Izh2p negatively regulates the expression of a gene involved in iron uptake called FET3 (Kupchak et al, 2007). The reason for Izh2p-dependent regulation of FET3 is still poorly understood; however, it is not critical to the goals of this study to understand why Izh2p regulates FET3.…”

Xenopus oocyte prophase I meiotic arrest is released independently from a decrease in cAMP levels or PKA activity

“…meiotic arrest. mPRs and AdipoQ receptors can functionally couple to the same signal transduction pathway in yeast, suggesting a common mechanism of action (Kupchak et al, 2007). Adiponectin receptors signal through multiple pathways, including the adaptor protein APPL1, which links to the trafficking GTPase Rab5 (Buechler et al, 2010;Mao et al, 2006) or p38 MAPK (MAPK14) (Heiker et al, 2010).…”