p56lck phosphorylation by Ca2+/calmodulin-dependent protein kinase type II

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• Calcium/calmodulin-dependent protein kinases (CaMKs) are crucial regulators of T cell activation and thymocyte selection.
• T cell receptor signaling involves the activation of the protein tyrosine kinase p56lck.
• T cell activation and IL-2 receptor signaling lead to Ca(2+)-mediated phosphorylation of p56lck on serine/threonine residues.

Purpose of the Study:

• To investigate the role of CaM kinase-II and CaM kinase-Gr in T cell signaling.
• To determine if CaM kinase-II or CaM kinase-Gr can phosphorylate the T cell tyrosine kinase p56lck.
• To assess the impact of CaM kinase-II-mediated phosphorylation on p56lck activity.

Main Methods:

• Investigated the presence of CaM kinase-II and CaM kinase-Gr isoforms in human T lymphocytes.
• Performed in vitro kinase assays using purified CaM kinase-II and CaM kinase-Gr with p56lck.
• Utilized tryptic phosphopeptide mapping to identify phosphorylation sites on p56lck.
• Assessed the phosphotransfer activity of p56lck after modification by CaM kinase-II.

Main Results:

• Both CaM kinase-II and CaM kinase-Gr were found in human T lymphocytes.
• CaM kinase-II, but not CaM kinase-Gr, phosphorylated p56lck in vitro.
• Tryptic phosphopeptide mapping revealed multiple phosphorylation sites on p56lck by CaM kinase-II.
• CaM kinase-II modification did not significantly alter the phosphotransfer activity of p56lck.

Conclusions:

• CaM kinase-II is capable of phosphorylating the T cell tyrosine kinase p56lck.
• The phosphorylation of p56lck by CaM kinase-II occurs at multiple sites.
• This phosphorylation event does not appear to modulate the catalytic activity of p56lck.