Ambient pH Controls Glycogen Levels by Regulating Glycogen Synthase Gene Expression in Neurospora crassa. New Insights into the pH Signaling Pathway

Author(s)

Cupertino, Fernanda Barbosa ^[1] ; Freitas, Fernanda Zanolli ^[1] ; de Paula, Renato Magalhaes ^[2] ; Bertolini, Maria Celia ^[1]

Affiliation

^[1] Univ Estadual Paulista, UNESP, Inst Quim, Dept Bioquim & Tecnol Quim, Sao Paulo - Brazil

^[2] Nalco Co, Sugar Land, TX - USA

• Document type: Journal article
• Source: PLoS One; v. 7, n. 8 AUG 31 2012.
• Web of Science Citations: 18

Abstract

Glycogen is a polysaccharide widely distributed in microorganisms and animal cells and its metabolism is under intricate regulation. Its accumulation in a specific situation results from the balance between glycogen synthase and glycogen phosphorylase activities that control synthesis and degradation, respectively. These enzymes are highly regulated at transcriptional and post-translational levels. The existence of a DNA motif for the Aspergillus nidulans pH responsive transcription factor PacC in the promoter of the gene encoding glycogen synthase (gsn) in Neurospora crassa prompted us to investigate whether this transcription factor regulates glycogen accumulation. Transcription factors such as PacC in A. nidulans and Rim101p in Saccharomyces cerevisiae play a role in the signaling pathway that mediates adaptation to ambient pH by inducing the expression of alkaline genes and repressing acidic genes. We showed here that at pH 7.8 pacC was overexpressed and gsn was down-regulated in wild-type N. crassa coinciding with low glycogen accumulation. In the pacC(KO) strain the glycogen levels and gsn expression at alkaline pH were, respectively, similar to and higher than the wild-type strain at normal pH (5.8). These results characterize gsn as an acidic gene and suggest a regulatory role for PACC in gsn expression. The truncated recombinant protein, containing the DNA-binding domain specifically bound to a gsn DNA fragment containing the PacC motif. DNA-protein complexes were observed with extracts from cells grown at normal and alkaline pH and confirmed by ChIP-PCR analysis. The PACC present in these extracts showed equal molecular mass, indicating that the protein is already processed at normal pH, in contrast to A. nidulans. Together, these results show that the pH signaling pathway controls glycogen accumulation by regulating gsn expression and suggest the existence of a different mechanism for PACC activation in N. crassa. (AU)

• FAPESP's process: 08/57566-8 - The Neurospora crassa filamentous fungus as a model organism for the identification and characterization of new proteins/transcription factors regulating the glycogen metabolism
• Grantee: Maria Celia Bertolini
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 07/07766-8 - Functional characterization of transcription factors involved in the glycogen metabolism regulation in Neurospora crassa
• Grantee: Fernanda Barbosa Cupertino
• Support Opportunities: Scholarships in Brazil - Doctorate