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Okadaic acid inhibits dephosphorylation of cytoplasmic p53 during lymphocyte activation
J E McClure1, C A Noonan, W T Shearer
1Department of Pediatrics, Baylor College of Medicine, Houston, Texas.
Abstract:
A competition radioimmunoassay specific for conserved Domain V of p53 revealed that Domain V was masked in highly phosphorylated cytosolic p53 of resting T lymphocytes and unmasked through dephosphorylation during lymphocyte activation. Phosphatase type 2A was shown to act upon immunopurified p53 in a manner that increased the immunoreactivity of the molecule in the Domain V RIA. Treatments of T cells with okadaic acid (1nM) prior to addition of Concanavalin-A/serum inhibited completely the dephosphorylation of cytosolic p53 observed to occur within 10-20min of stimulation. Brief exposure of T cells to okadaic acid during the first hour of activation by mitogens produced increased rates of cellular proliferation. Sustained inhibition of the dephosphorylation of cytoplasmic p53 in cells undergoing mitogenic stimulation may affect adversely the ability of p53 to exert its anti-proliferative effect and could contribute to unregulated cell growth.
Insights
p53 protein phosphorylation controls its function in T lymphocytes. Dephosphorylation during activation unmasks p53 Domain V, impacting cell proliferation. Inhibiting this process may lead to unregulated cell growth.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Cytosolic p53 phosphorylation status influences T lymphocyte function.
- The role of p53 Domain V in lymphocyte activation is not fully understood.
Purpose of the Study:
- To investigate the role of p53 Domain V masking and unmasking during T lymphocyte activation.
- To determine the effect of dephosphorylation on p53 function and cellular proliferation.
Main Methods:
- Competition radioimmunoassay (RIA) specific for p53 Domain V.
- Immunopurification of p53.
- Treatment of T cells with okadaic acid (a phosphatase inhibitor) and mitogens (Concanavalin-A/serum).
Main Results:
- p53 Domain V is masked in phosphorylated cytosolic p53 of resting T lymphocytes.
- Dephosphorylation during lymphocyte activation unmasks p53 Domain V, increasing immunoreactivity.
- Okadaic acid treatment inhibited p53 dephosphorylation and enhanced cellular proliferation rates.
- Sustained inhibition of p53 dephosphorylation may impair its anti-proliferative effect.
Conclusions:
- p53 Domain V unmasking via dephosphorylation is a key event during T lymphocyte activation.
- Modulating p53 dephosphorylation impacts T cell proliferation.
- Inhibition of p53 dephosphorylation may contribute to uncontrolled cell growth.