Da. Fruman et al., CHARACTERIZATION OF A MUTANT CALCINEURIN A-ALPHA GENE EXPRESSED BY EL4 LYMPHOMA-CELLS, Molecular and cellular biology, 15(7), 1995, pp. 3857-3863
The calmodulin-stimulated phosphatase calcineurin plays a critical rol
e in calcium-dependent T-lymphocyte activation pathways. Here, we repo
rt the identification of a missense mutation in the calcineurin A alph
a gene expressed by EL4 T-lymphoma cells. This mutation changes an evo
lutionarily conserved aspartic acid to asparagine within the autoinhib
itory domain of the calcineurin A alpha protein. A comparison of wild-
type and mutant autoinhibitory peptides indicates that this amino acid
substitution greatly reduces inhibition of calcineurin phosphatase ac
tivity. Additional peptide inhibition studies support a pseudosubstrat
e model of autoinhibitory function, in which the conserved aspartic ac
id residue may serve as a molecular mimic of either phosphoserine or p
hosphothreonine. Expression of the mutant calcineurin appears to affec
t cellular signal transduction pathways, as EL4 cells can be activated
by suboptimal concentrations of calcium ionophore in the presence of
phorbol esters. Moreover, this phenotype can be transferred to Jurkat
T cells by transfection of the mutated calcineurin gene. These finding
s implicate a conserved aspartic acid in the mechanism of calcineurin
autoinhibition and suggest that mutation of this residue is associated
with aberrant calcium-dependent signaling in vivo.