Identification of Translational Regulation Target Genes during Filamentous Growth in Saccharomyces cerevisiae : Regulatory Role of Caf20 and Dhh1

Abstract

The dimorphic transition of yeast to the hyphal form is regulated by the mitogen-activated protein kinase and cyclic AMP-dependent protein kinase A pathways in Saccharomyces cerevisiae. Signaling pathway-responsive transcription factors such as Ste12, Tec1, and Flo8 are known to mediate filamentation-specific transcription. We were interested in investigating the translational regulation of specific mRNAs during the yeast-tohyphal-form transition. Using polyribosome fractionation and RT-PCR analysis, we identified STE12, GPA2, and CLN1 as translation regulation target genes during filamentous growth. The transcript levels for these genes did not change, but their mRNAs were preferentially associated with polyribosomes during the hyphal transition. The intracellular levels of Ste12, Gpa2, and Cln1 proteins increased under hyphal-growth conditions. The increase in Ste12 protein level was partially blocked by mutations in the CAF20 and DHH1 genes, which encode an eIF4E inhibitor and a decapping activator, respectively. In addition, the caf20 and dhh1 mutations resulted in defects in filamentous growth. The filamentation defects caused by caf20 and dhh1 mutations were suppressed by STE12 overexpression. These results suggest that Caf20 and Dhh1 control yeast filamentation by regulating STE12 translation.The cellular morphology of diploid Saccharomyces cerevisiae frequently switches between the yeast and filamentous forms depending on nutritional signals (16). Several signal transduction modules, including the mitogen-activated protein kinase (MAPK) cascade and the cyclic AMP-dependent protein kinase A (PKA) pathway, are known to participate in this switch (14,21,31,36). The MAPK cascade involves Ste20, Ste11, Ste7, Kss1, and the transcription factors Ste12 and Tec1 (15,21,29,30). The PKA pathway involves Gpr1, Gpa2, Ras2, Tpk2, and the transcription factors Flo8 and Sfl1 (22,26,31,32). These signaling pathways control the transcription of a number of filamentation-specific genes, including FLO11 (19,23,29).Although the signaling pathways and transcriptional regulation of yeast filamentous growth have been studied in considerable detail, little is known about translational regulation related to the transition from the yeast to the filamentous form. In this study, we searched for specific mRNAs that are preferentially translated during the yeast-to-hyphal-form transition. Genome-wide analysis of mRNA translation profiles indicates that the loading of ribosomes onto individual mRNA species varies broadly (20, 28). The association of mRNA transcripts in polyribosomes reflects the rate of synthesis of their corresponding proteins (3, 45). By purifying polyribosome fractions and employing RT-PCR analysis, we found that the mRNA transcripts of STE12, GPA2, and CLN1 were preferentially recruited to polyribosomes during filamentation compared to during normal vegetative growth, even though their levels in the total cell extracts were not changed. Consistently, the protein levels of Ste12, Gpa2, and Cln1 also increased during...

The mRNA Decay Pathway Regulates the Expression of the Flo11 Adhesin and Biofilm Formation inSaccharomyces cerevisiae

“…All mutants were compromised for adhesion to 2% agar plates, albeit to a different degree, and pop2Δ and dhh1Δ also for invasion ( Figure S2). In agreement with our data, defective adherence to agar for the dhh1Δ strain has been previously observed (Park et al 2006).…”

Gcn4 Is Required for the Response to Peroxide Stress in the Yeast Saccharomyces cerevisiae

“…Two such proteins have been identified in yeast, Caf20 and Eap1 (Altmann et al, 1997;Cosentino et al, 2000). These 4E-BPs have broad functions in cell growth, proliferation, and development (Ibrahimo et al, 2006;Park et al, 2006). Disruption of EAP1 (but not CAF20) was found to impair cadmiumand diamide-induced regulation of translation initiation.…”

The Saccharomyces Homolog of Mammalian RACK1, Cpc2/Asc1p, Is Required for FLO11-dependent Adhesive Growth and Dimorphism

“…These include Caf20p and Eap1p, the decapping activator Dhh1p, and the RNA helicase eIF4A (78,79). It is tempting to speculate that the eIF4G-interacting protein Cpc2p might have a similar role in derepressing translation of specific transcripts and that the underlying mechanism requires various kinases and eIF2␣, eIF4A, and the RAC subunit Ssz1p as targets for these kinases.…”