A Novel Specificity Protein 1 (SP1)-like Gene Regulating Protein Kinase C-1 (Pkc1)-dependent Cell Wall Integrity and Virulence Factors in Cryptococcus neoformans

Abstract

Eukaryotic cells utilize complex signaling systems to detect their environments, responding and adapting as new conditions arise during evolution. The basidiomycete fungus Cryptococcus neoformans is a leading cause of AIDS-related death worldwide and utilizes the calcineurin and protein kinase C-1 (Pkc1) signaling pathways for host adaptation and expression of virulence. In the present studies, a C-terminal zinc finger transcription factor, homologous both to the calcineurin-responsive zinc fingers (Crz1) of ascomycetes and to the Pkc1-dependent specificity protein-1 (Sp1) transcription factors of metazoans, was identified and named SP1 because of its greater similarity to the metazoan factors. Structurally, the Cryptococcus neoformans Sp1 (Cn Sp1) protein was found to have acquired an additional zinc finger motif from that of Crz1 and showed Pkc1-dependent phosphorylation, nuclear localization, and whole genome epistatic associations under starvation conditions. Transcriptional targets of Cn Sp1 shared functional similarities with Crz1 factors, such as cell wall synthesis, but gained the regulation of processes involved in carbohydrate metabolism, including trehalose metabolism, and lost others, such as the induction of autophagy. In addition, overexpression of Cn Sp1 in a pkc1⌬ mutant showed restoration of altered phenotypes involved in virulence, including cell wall stability, nitrosative stress, and extracellular capsule production. Cn Sp1 was also found to be important for virulence of the fungus using a mouse model. In summary, these data suggest an evolutionary shift in C-terminal zinc finger proteins during fungal evolution, transforming them from calcineurin-dependent to PKC1-dependent transcription factors, helping to shape the role of fungal pathogenesis of C. neoformans.

Rewiring of Signaling Networks Modulating Thermotolerance in the Human Pathogen Cryptococcus neoformans

“…One is CNAG_01727 and the other is CNAG_01750. Adler et al (2011) first characterized CNAG_01727 (named Ssa1), which is orthologous to an Hsp70 member protein, Ssa1, in S. cerevisiae. Intriguingly, Ssa1 is a DNA-binding transcriptional coactivator of laccase in C. neoformans (Zhang et al 2006).…”

ALL2 , a Homologue of ALL1 , Has a Distinct Role in Regulating pH Homeostasis in the Pathogen Cryptococcus neoformans

“…Next, we sought to investigate whether All1p and All2p proteins colocalize, since both the ALL1 and the ALL2 transcripts are coregulated (9). For these studies, ALL2 was fused with C. neoformans codon-optimized mCherry under an ACT1 promoter (ALL2-mCherry).…”

“…Loss of ALL1 function resulted in a hypervirulent phenotype in both serotype A-and D-null mutants (all1⌬). Furthermore, it was shown that ALL1 is regulated during capsule induction (8) and by the transcription factor Sp1 and the PKC1 gene under glucose starvation (9), as well as by CIR1 in response to changes in iron concentration (10). Under starvation, VAD1 downregulates ALL1 transcripts via degradation of mRNA (11).…”

“…Extensive homology search for ALL1 revealed a highly homologous uncharacterized cryptococcal gene, CNM02200 (JEC21), which was subsequently named ALL2. Similarly to ALL1, ALL2 is also regulated by Sp1 and PKC1 under glucose starvation and during capsule induction (9).…”

Calcineurin in fungal virulence and drug resistance: Prospects for harnessing targeted inhibition of calcineurin for an antifungal therapeutic approach

“…To date, one of the well characterized substrates of calcineurin is the mammalian NFAT ortholog, Crz1, which mediates transcriptional response triggered by calcineurin activation in response to stress conditions in Candida species, C. neoformans 64,[95][96][97] and A. fumigatus. 98,99 As mentioned earlier, another important binding partner of calcineurin is the calcineurin binding protein, Cbp1, an element involved in fine tuning of calcineurin signaling that was also characterized from C. neoformans and A. fumigatus.…”