Role of calcium calmodulin kinases in modification of the p53 signalling pathway
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Date
2009Author
Faulkner, Jennifer A.
Metadata
Abstract
P53 is a tetrameric transcription factor which exhibits DNA binding activity through its
core domain which encompasses the conserved domains (known as Box II, III, IV and
V). The N-terminal domain of p53 provides a scaffold for binding of components of the
transcriptional machinery. Phosphorylation at residues within the N-terminal
transactivation domain of p53 such as Serine 20 is a crucial event in the activation of
p53. It stabilises the binding of the co-activator p300, reduces the binding of the
inhibitory partner Mdm2 and enhances activation of p53 target genes. The identification
of enzymes that phosphorylate p53 transactivation domain is an important development
in the ongoing mapping of signaling pathways that control p53-dependent transcription
and resultant tumour suppression. Environmental and physiological stresses activate
p53 which has led to the creation of several hypothetical models in which tumour
suppressor kinases mediate p53 activation by phosphorylation at Serine 20. Although
much researched the identity of the main Serine 20 kinase in cells remains undefined. In
this study we have identified Calcium Calmodulin kinase superfamily (CAMK)
members as potent Serine 20 kinases in cells and show that the co-transfection of p53
peptides derived from the conserved domains can modify this response. Moreover, we
show that the multi-protein docking site, p53 Box V domain, is required for Serine 20
phosphorylation and ubiquitination of p53. To further define the domains required for
the interaction of p53 with CAMK superfamily members, mutagenesis of p53 was
performed. Using transcriptional and binding based assays we were able to establish
that p53 does indeed form an interaction with Chk1 and DAPK1. Development of cell
models and gene expression studies demonstrated that depletion of Chk1 and DAPK1
results in activation of the p53 signalling pathway. There may therefore be a role for
kinases as negative regulators of p53 and a potential for the development of kinases as
drug targets for reactivation of the p53 pathway.