Efg1 Directly RegulatesACE2Expression To Mediate Cross Talk between the cAMP/PKA and RAM Pathways during Candida albicans Morphogenesis

Abstract

The cyclic AMP/protein kinase A (cAMP/PKA) and regulation of Ace2 and morphogenesis (RAM) pathways are important regulators of the yeast-to-hypha transition in Candida albicans that interact genetically during this process. To further understand this interaction, we have characterized the expression of ACE2 during morphogenesis. In normoxic, planktonic conditions, ACE2 expression is very low in stationary-phase cells at both the mRNA and protein levels. Upon shifting to Spider medium, ACE2/Ace2p levels increase. Although Ace2 is not absolutely required for hypha formation, ace2⌬/⌬ mutants show delayed hypha formation in Spider medium (but not others) and morphological changes to the hyphal tip and lateral yeast. We also show that Efg1 directly binds the promoter of Ace2 in stationary phase, and ACE2 levels are increased in strains lacking Efg1 and the protein kinase A proteins Tpk1 and Tpk2, indicating that the PKA pathway directly regulates ACE2 expression. ACE2 expression is positively regulated by Tec1 and Brg1, which bind the promoters of ACE2 in hyphal cells but not in the yeast phase. Under embedded conditions, Efg1 is dispensable for filamentation and Ace2 is required. We have found that ACE2 expression is much higher in embedded cells than in planktonic cells, providing a potential rationale for this observation. Taken together, our observations indicate that the PKA pathway directly regulates the RAM pathway under specific conditions and are consistent with a model where the two pathways carry out similar functions that depend on the specific environmental context.

Candida albicans responds to glycostructure damage by Ace2‐mediated feedback regulation of Cek1 signaling

“…Ace2 was first identified in S. cerevisiae as target of the regulation of Ace2 and morphogenesis (RAM) pathway, which is conserved in fungi and ensures cell separation (Kurischko et al, 2005). Recently, cross-interaction of the RAM pathway with the PKA pathway was reported, in which Ace2 and the major hyphal regulator Efg1 determine morphogenesis of C. albicans in specific environments (Wang et al, 2009;Bharucha et al, 2011;Saputo et al, 2014;Desai et al, 2015). In this article we report that the transcription factor Ace2 functions downstream of the Cek1 MAP kinase pathway and is required to overcome impaired N-and O-glycosylation in C. albicans.…”

Complex Haploinsufficiency-Based Genetic Analysis of the NDR/Lats Kinase Cbk1 Provides Insight into Its Multiple Functions in Candida albicans

“…The Cbk1-Ace2 axis affects serum-induced filamentation One of our hypotheses at the outset of this screen was that a serum-based screen would identify unique CBK1 interactors because Ace2 was not required for filamentation (Kelly et al 2004) on serum but did affect Spider medium-induced filamentation (Saputo et al 2014). In our Spider medium screen, we identified a large number of Ace2 targets as CBK1 interactors.…”

“…In contrast, reduced gene dosage of the transcriptional regulator Ace2 affects that expression of the entire set of targets and, through this more global effect, leads to activation of compensatory pathways. Specifically, we have previously shown that the PKA pathway is hyperactivated in the absence of a fully functional Cbk1-Ace2 axis (Bharucha et al 2011) and contributes to the increased filamentation of ace2D/D under noninducing conditions (Saputo et al 2014). We further propose that one of the advantages of haploinsufficient phenotypes is that they may reveal subtle effects of pathways that otherwise may be overwhelmed by the compensatory response to complete loss of that pathway.…”

“…It is, however, important to note that the serum screen identified Efg1 and the Spider medium screen revealed that the RAM pathway and the PKA pathway interact during morphogenesis (Bharucha et al 2011). Subsequent work in our laboratory has also shown that Efg1, the major transcriptional regulator of the PKA pathway, directly regulates the expression of Ace2 (Saputo et al 2014). Interestingly, despite the almost entirely distinct natures of the individual genes identified by screens in the two conditions, the major GO terms enriched in the data sets were identical: regulation of metabolism and filamentation.…”

“…Gutierrez-Escribino et al (2011) have shown that Cdc28 phosphorylates Mob2 and Cdc28 also regulates Fkh2 (Grieg et al 2015), indicating that the RAM pathway as well as its output are interconnected with this important cell cycle regulator. In a previous application of complex haploinsufficiency screening to Cbk1 (Bharucha et al 2011), we found that the RAM and PKA-cAMP pathways interact and subsequent mechanistic studies revealed that Efg1 (FungiDB: orf19.610 ), the main transcription factor regulated by the cAMP-PKA pathway, suppresses ACE2 expression early in morphogenesis (Saputo et al 2014). The previous complex haploinsufficiency screen was performed using Spider medium as the filament-inducing conditions (Bharucha et al 2011) and, in addition to revealing the PKA pathway interaction, identified a large number of Ace2 targets.…”