Control of Signaling in a MAP-kinase Pathway by an RNA-Binding Protein

Abstract

Signaling-protein mRNAs tend to have long untranslated regions (UTRs) containing binding sites for RNA-binding proteins regulating gene expression. Here we show that a PUF-family RNA-binding protein, Mpt5, represses the yeast MAP-kinase pathway controlling differentiation to the filamentous form. Mpt5 represses the protein levels of two pathway components, the Ste7 MAP-kinase kinase and the Tec1 transcriptional activator, and negatively regulates the kinase activity of the Kss1 MAP kinase. Moreover, Mpt5 specifically inhibits the output of the pathway in the absence of stimuli, and thereby prevents inappropriate cell differentiation. The results provide an example of what may be a genome-scale level of regulation at the interface of signaling networks and protein-RNA binding networks.

Mutations in the Saccharomyces cerevisiae Kinase Cbk1p Lead to a Fertility Defect That Can Be Suppressed by the Absence of Brr1p or Mpt5p (Puf5p), Proteins Involved in RNA Metabolism

“…Deletion of BRR1 leads to a modest hyperpolarization in a CBK1 background (axial ratio 1.29 compared to 1.2 for the wild type) and a limited restoration of polarity in cbk1T3HA or Dcbk1. In contrast, deletion of MPT5 leads to a clear hyperpolarization (axial ratio 1.43 compared to 1.2 for the wild type, Figure 5; see also Prinz et al 2007) and restores cellular polarity in a cbk1T3HA or Dcbk1 background, leading to a slightly hyperpolarized axial ratio (1.3 and 1.29 compared to 1.2 for the wild-type strain).…”

“…Several Mpt5p mRNA targets are well characterized such as HO, involved in mating type switching, and STE7 and TEC1, two components of the (f )-MAPK pathway. Mpt5p has also been implicated in the regulation of many other pathways, such as silencing and replicative life span, although the mechanisms involved remain unclear (Kennedy et al 1997;Cockell et al 1998;Tadauchi et al 2001;Irie et al 2002;Ohkuni et al 2006;Prinz et al 2007). Mpt5p also regulates, at least in part, the cell wall integrity (CWI) pathway.…”

“…Finally, the deletion of MPT5 suppresses the mating defect of a fus3 mutant (Chen and Kurjan 1997;Bardwell 2005;Prinz et al 2007). In general Mpt5p seems to regulate pathways, or individual proteins, by binding to the 39-UTR of mRNAs, leading to degradation or a reduction of translation.…”

“…In cbk1T3HA cells, Dmpt5 stimulates the expression of some of the mating type-specific genes, restores polarity, and accelerates the mating process. Prinz et al (2007) have shown that the hyperpolarization of Dmpt5 strains requires the presence of TEC1. In conjunction with Ste12p, Tec1p activates the filamentation pathway; Mpt5p binds the TEC1 mRNA and inhibits the expression of Tec1p.…”

Patterns and plasticity in RNA-protein interactions enable recruitment of multiple proteins through a single site

“…A six-flipped site, which binds Puf5p, will continue to be controlled even under conditions in which Puf4p is down-regulated. Interactions between Puf5p and components of signaling pathways suggest it may respond to signals that Puf4p does not (45,46). PUF protein networks hinge on the specificity of PUF-RNA interactions.…”