Abstract
In filamentous fungi, intracellular signaling pathways which are mediated by changing calcium levels and/or by activated protein kinase C (Pkc), control fungal adaptation to external stimuli. A rise in intracellular Ca2+ levels activates calcineurin subunit A (CnaA), which regulates cellular calcium homeostasis among other processes. Pkc is primarily involved in maintaining cell wall integrity (CWI) in response to different environmental stresses. Cross-talk between the Ca2+ and Pkc-mediated pathways has mainly been described in Saccharomyces cerevisiae and in a few other filamentous fungi. The presented study describes a genetic interaction between CnaA and PkcA in the filamentous fungus Aspergillus nidulans. Overexpression of pkcA partially rescues the phenotypes caused by a cnaA deletion. Furthermore, CnaA appears to affect the regulation of a mitogen-activated kinase, MpkA, involved in the CWI pathway. Reversely, PkcA is involved in controlling intracellular calcium homeostasis, as was confirmed by microarray analysis. Furthermore, overexpression of pkcA in a cnaA deletion background restores mitochondrial number and function. In conclusion, PkcA and CnaA-mediated signaling appear to share common targets, one of which appears to be MpkA of the CWI pathway. Both pathways also regulate components involved in mitochondrial biogenesis and function. This study describes targets for PkcA and CnaA-signaling pathways in an A. nidulans and identifies a novel interaction of both pathways in the regulation of cellular respiration.
Highlights
Cellular responses to environmental stimuli are often mediated through G-proteins, which consist of a G-protein coupled receptor (GPCR) and the associated heterotrimeric G-proteins [1]
The alcA::pkcA DcnaA strain was constructed by sexually crossing an alcA::pkcA strain with a DcnaA strain
The pkcA mRNA accumulation is increased about 3 to 42fold when alcA::pkcA and alcA::pkcA DcnaA growth in 2% glycerol+ 100 mM threonine was compared to glucose 2% for both, respectively (Figure 1)
Summary
Cellular responses to environmental stimuli are often mediated through G-proteins, which consist of a G-protein coupled receptor (GPCR) and the associated heterotrimeric G-proteins [1]. One such G-protein is phospholipase C which produces the second messengers diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3) from the cell membrane phospholipid phosphatidylinositol 4,5-bisphosphate. These second messengers subsequently cause an increase in intracellular Ca2+ levels [2]. A rise in intracellular Ca2+ levels causes the activation of the calcineurin phosphatase and the protein kinase C (Pkc) pathways [2]. Crosstalk between Pkc and the unfolded protein response (UPR) or other MAP (mitogen-activated protein) kinase cascades has been observed [10,11]
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