Differential Regulation of the Cell Wall Integrity Mitogen-Activated Protein Kinase Pathway in Budding Yeast by the Protein Tyrosine Phosphatases Ptp2 and Ptp3

Abstract

Mitogen-activated protein kinases (MAPKs) are inactivated by dual-specificity and protein tyrosine phosphatases (PTPs) in yeasts. In Saccharomyces cerevisiae, two PTPs, Ptp2 and Ptp3, inactivate the MAPKs, Hog1 and Fus3, with different specificities. To further examine the functions and substrate specificities of Ptp2 and Ptp3, we tested whether they could inactivate a third MAPK, Mpk1, in the cell wall integrity pathway. In vivo and in vitro evidence indicates that both PTPs inactivate Mpk1, but Ptp2 is the more effective negative regulator. Multicopy expression of PTP2, but not PTP3, suppressed growth defects due to the MEK kinase mutation, BCK1-20, and the MEK mutation, MKK1-386, that hyperactivate this pathway. In addition, deletion of PTP2, but not PTP3, exacerbated growth defects due to MKK1-386. Other evidence supported a role for Ptp3 in this pathway. Expression of MKK1-386 was lethal in the ptp2⌬ ptp3⌬ strain but not in either single PTP deletion strain. In addition, the ptp2⌬ ptp3⌬ strain showed higher levels of heat stress-induced Mpk1-phosphotyrosine than the wild-type strain or strains lacking either PTP. The PTPs also showed differences in vitro. Ptp2 was more efficient than Ptp3 at binding and dephosphorylating Mpk1. Another factor that may contribute to the greater effectiveness of Ptp2 is its subcellular localization. Ptp2 is predominantly nuclear whereas Ptp3 is cytoplasmic, suggesting that active Mpk1 is present in the nucleus. Last, PTP2 but not PTP3 transcript increased in response to heat shock in a Mpk1-dependent manner, suggesting that Ptp2 acts in a negative feedback loop to inactivate Mpk1.

Reciprocal Regulation between Slt2 MAPK and Isoforms of Msg5 Dual-specificity Protein Phosphatase Modulates the Yeast Cell Integrity Pathway

“…In yeast, consistent with its role in adaptation of the mating pathway, Msg5 transcription is up-regulated in response to pheromone treatment (14). Although the existence of adaptation in the cell integrity pathway has been reported in a particular background (9), in most of the strains the level of phosphorylated Slt2 remained high and does not decrease for several hours upon stim- ulation (15,36). The absence of an increase in MSG5 transcription following heat shock is consistent with the lack of a Msg5-mediated negative feedback mechanism in this signaling pathway.…”

“…In all of the strains tested, the exploration of dual Slt2 phosphorylation before and during thermal treatment in a wild type and a msg5 strain revealed that Msg5 played a fundamental role in down-regulating the basal activity of Slt2. The absence of either Ptp2 or Ptp3 does not lead to a significant increase in the amount of basal dually phosphorylated Slt2 (9,16). Furthermore, the dual-specificity protein phosphatase Sdp1 does not seem to be involved in maintaining a low basal Slt2 phosphorylation (16).…”

“…For example, the tyrosine phosphatases Ptp2 and Ptp3 have been shown to down-regulate the mating, the HOG, and the cell integrity pathways in S. cerevisiae by acting on Fus3, Hog1, and Slt2 MAPKs, respectively (7)(8)(9)(10). Furthermore, the same protein phosphatase is able to regulate a pathway at different stages of the signaling process.…”

In Saccharomyces cerevisiae an unbalanced level of tyrosine phosphorylation down-regulates the Ras/PKA pathway

“…Protein tyrosine phosphatases and dual specificity phosphatases are known to affect MAPKs activity in yeast. For instance, Ptp2 and Ptp3 affect localization of the Hog1 MAPK, but are also known to regulate Fus3 and Slt2 (Mattison & Ota, 2000;Mattison, Spencer, Kresge, Lee, & Ota, 1999;Zhan, Deschenes, & Guan, 1997). The upper part of the Ste/MAPK cascade is shared between the pseudohyphal/invasive growth pathway and the mating pheromone response pathway and Kss1, the MAPK of the pseudohyphae/invasive growth module, has been indicated as a bona fide component of the mating pathway (Breitkreutz & Tyers, 2002).…”

Cell Differentiation and Spatial Organization in Yeast Colonies: Role of Cell-Wall Integrity Pathway

“…( Mattison et al 1999). Based on the high levels of colony sporulation in the W303 strain background and the involvement of multiple components of the CWI pathway in this sporulation, the W303 background was used for all remaining experiments in this study.…”