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A conserved family of calcineurin regulators
T J Kingsbury1, K W Cunningham
1Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.
Abstract:
The protein phosphatase calcineurin mediates many cellular responses to calcium signals. Using a genetic screen in yeast, we identified a new family of proteins conserved in fungi and animals that inhibit calcineurin function when overexpressed. Overexpression of the yeast protein Rcn1p or the human homologs DSCR1 or ZAKI-4 inhibited two independent functions of calcineurin in yeast: The activation of the transcription factor Tcn1p and the inhibition of the H(+)/Ca(2+) exchanger Vcx1p. Purified recombinant Rcn1p and DSCR1 bound calcineurin in vitro and inhibited its protein phosphatase activity. Signaling via calmodulin, calcineurin, and Tcn1p induced Rcn1p expression, suggesting that Rcn1p operates as an endogenous feedback inhibitor of calcineurin. Surprisingly, rcn1 null mutants exhibited phenotypes similar to those of Rcn1p-overexpressing cells. This effect may be due to lower expression of calcineurin in rcn1 mutants during signaling conditions. Thus, Rcn1p levels may fine-tune calcineurin signaling in yeast. The structural and functional conservation between Rcn1p and DSCR1 suggests that the mammalian Rcn1p-related proteins, termed calcipressins, will modulate calcineurin signaling in humans and potentially contribute to disorders such as Down Syndrome.
Insights
Researchers discovered Rcn1p, a conserved protein that acts as a feedback inhibitor for calcineurin signaling. This finding reveals a new mechanism for regulating calcium responses and may offer insights into Down Syndrome.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Calcineurin is a crucial protein phosphatase regulating cellular responses to calcium signals.
- Understanding calcineurin's regulation is vital for deciphering various cellular processes.
Purpose of the Study:
- To identify novel regulators of calcineurin function.
- To investigate the role of a newly identified protein family in calcineurin signaling.
Main Methods:
- Genetic screening in yeast to identify calcineurin inhibitors.
- Biochemical assays using purified recombinant proteins (Rcn1p, DSCR1) to assess calcineurin inhibition.
- Analysis of gene expression changes in yeast strains with altered Rcn1p levels.
Main Results:
- A conserved protein family, including yeast Rcn1p and human DSCR1/ZAKI-4, was identified as calcineurin inhibitors.
- Overexpression of Rcn1p or DSCR1 inhibited key calcineurin functions in yeast.
- Purified Rcn1p and DSCR1 directly bound and inhibited calcineurin's phosphatase activity in vitro.
- Rcn1p expression is induced by calcineurin signaling, indicating a feedback inhibition loop.
- Rcn1 null mutants showed phenotypes similar to overexpression, suggesting complex regulation of calcineurin levels.
Conclusions:
- Rcn1p acts as an endogenous feedback inhibitor of calcineurin, fine-tuning calcium signaling in yeast.
- The conserved nature of Rcn1p and its human homologs (calcipressins) suggests a similar role in mammalian systems.
- Dysregulation of calcipressins may contribute to human disorders like Down Syndrome.