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Global regulatory roles of the cAMP/PKA pathway revealed by phenotypic, transcriptomic, and phosphoproteomic analyses in a null mutant of PKA catalytic subunit in Candida albicans

ABSTRACT: The conserved cAMP-dependent protein kinase (PKA) holoenzyme is composed of two catalytic and two regulatory subunits. It plays critical roles in the regulation of many biological processes in eukaryotic organisms. In the human fungal pathogen Candida albicans, the PKA kinase has been extensively investigated for its importance in the regulation of morphological transitions and virulence. It has been long thought that the PKA catalytic subunit is essential for cell viability in C. albicans. Paradoxically, the single adenylyl cyclase-encoding gene, CRY1, which is required for the production of cAMP in C. albicans, is not essential for cell growth. In this study, we successfully generated a null double mutant of TPK1 and TPK2 (tpk2/tpk2 tpk1/tpk1 or t2t1), which encode two isoforms of the PKA catalytic subunit in C. albicans. We reevaluated the roles of the PKA catalytic subunit in cell growth and phenotypic transitions. Inactivation of the PKA catalytic subunit by deletion of both TPK1 and TPK2 blocked filamentation and dramatically attenuated the ability of white-to-opaque switching, but promoted sexual mating in C. albicans. Tpk2 plays a major role in these regulations, while Tpk1 generally functions as a negative regulator in morphological transitions and sexual mating. A comparative transcriptomic analysis demonstrated that the t2t1 and cyr1/cyr1 mutants exhibited similar global gene expression profiles. Compared to the WT strain, the general transcriptional activity and expression of genes involved in metabolism, translation, biosynthesis, adhesion and filamentation are significantly decreased in both the t2t1 and cyr1/cyr1 mutants. And a portion of stress-response and cell wall-related genes were upregulated in these mutants, which is consistent with their increased ability of anti-stresses. To further explore the global regulatory role of the PKA kinase, we performed quantitative phosphoproteomics analysis. Combining with bioinformatics analyses, we identified 181 potential PKA phosphorylation targets, which represent 148 unique proteins involved in a wide spectrum of biological processes. Cell wall and membrane-related proteins (e.g. Ecm3, Bni1, and Smi1) were enriched in Tpk1-specific targets, while Tpk2-specific substrates include transporters, filamentation and cytoskeleton-related proteins (e.g. Smf3, Sep7, and Mhp1). There were also many Tpk1 and Tpk2 overlapped and coordinately regulated-substrates. Our study clarifies the essentiality of the PKA catalytic subunit and shed new insights into the global regulatory features of the cAMP/PKA pathway in C. ablicans. The t2t1 null mutant generated in this study would also be a new resource for the field to study this important pathway.

ORGANISM(S): Candida albicans

PROVIDER: GSE92621 | GEO | 2017/08/18

SECONDARY ACCESSION(S): PRJNA358190

REPOSITORIES: GEO

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Project description:The pattern of gene transcription in Saccharomyces cerevisiae is strongly affected by the presence of glucose. An increased activity of protein kinase A (PKA), triggered by a rise in the intracellular concentration of cAMP, can account for many of the effects of glucose on transcription. To investigate the requirement of PKA for glucose control of gene expression, we have analyzed global transcription in strains devoid of PKA activity. In S. cerevisiae three genes, TPK1, TPK2, TPK3, encode catalytic subunits of PKA and the triple mutant tpk1 tpk2 tpk3 is unviable. We have worked, therefore, with two strains, tpk1 tpk2 tpk3 yak1 and tpk1 tpk2 tpk3 msn2 msn4, that bear suppressor mutations,. We have identified different classes of genes that can be induced, or repressed, by glucose in the absence of PKA. Among these genes, some are also controlled by a redundant signalling pathway involving PKA activation, while others do not respond to an increase in cAMP concentration. On the other hand, among genes which do not respond to glucose in the absence of PKA, some show a full response to increased cAMP levels, even in the absence of glucose, while others appear to require the cooperation of different signalling pathways. The goal of the present study was to investigate the occurrence of PKA-independent glucose signalling in S. cerevisiae. To this end, we have used global transcription analysis to study the effects of glucose on yeast strains completely devoid of PKA activity. In S. cerevisiae three genes TPK1, TPK2,and TPK3 encode catalytic subunits of PKA. While strains expressing only one of these genes grow normally, a triple null mutant (tpk1 tpk2 tpk3) is not viable (Toda et al 1987). Identification of different mutations able to suppress the growth defect of the triple mutant (Garrett and Broach 1989, Reinders et al 1998, Smith et al 1998) has allowed to determine what is the crucial function of PKA. As shown in Fig.1, PKA is needed to counteract the negative effect of the protein kinase Yak1 on yeast growth (Hartley et al 1994, Moriya et al 2001). In the presence of PKA the protein kinase Rim15 (Reinders et al 1998) and the transcription factors Msn2 and Msn4 (Görner et al 1998) can be phosphorylated and exported to the cytoplasm, transcription of the YAK1 gene, which is activated by Msn2/Msn4 (Smith et al 1998), is reduced, Yak1 levels remain low and growth is not hindered. In the absence of PKA, Rim15 remains in the nucleus where it can activate Msn2/Msn4 (Cameroni et al 2004) that turn on YAK1 transcription, thus blocking growth. This explains why strains lacking Rim15, Msn2/Msn4 or Yak1 no longer require PKA for growth. In this work we have used two isogenic strains lacking PKA and carrying the suppressor mutations msn2 msn4 or yak1. Two different suppressor mutants were used with the aim to enable a dissection of effects of the lack of PKA and effects of the suppressor mutations themselves.

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Global regulatory roles of the cAMP/PKA pathway revealed by phenotypic, transcriptomic, and phosphoproteomic analyses in a null mutant of PKA catalytic subunit in Candida albicans

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