Abstract
The control of phosphorylation by protein tyrosine kinases represents an important regulatory mechanism in T cell growth, function, and differentiation. We have identified a 62-kDa murine protein tyrosine kinase predominantly expressed within the T cell lineage, which we have termed Rlk (for Resting lymphocyte kinase). rlk mRNA was found to be expressed in the fetal thymus as early as day 13 of embryonic development as well as in adult thymus and mature resting peripheral T cells. The sequence of rlk showed that it is most closely related to the subfamily of cytoplasmic tyrosine kinases that includes the Btk, Itk, and Tec proteins. However, Rlk differs from these kinases by virtue of its unique aminoterminal domain, which lacks a region of pleckstrin homology common to the other members of this protein subfamily. Examination of rlk abundance within different T cell subpopulations revealed preferential expression in Th1 relative to Th2 T cell clones, suggesting a possible role in signal transduction pathways that selectively regulate cytokine production in mature CD4+ T cell subsets. Rlk thus represents a novel cytoplasmic tyrosine kinase with potential functions in intrathymic T cell development and mature T cell signaling.
Highlights
Response Modifiers Program, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702, the Departments of ftEndocrinology and ~~Pathology, University of Chicago, Chicago, Illinois 60637, the
We have identified a 62-kDa murine protein tyrosine kinase predominantly expressed within the T cell lineage, which we have termed Rlk. rlk mRNA was found to be expressed in the fetal thymus as early as day 13 of embryonic development as well as in adult thymus and mature resting peripheral T cells
Cloning and Sequencing of rlk cDNAs-A polymerase chain reaction (PCR)-based strategy was employed in order to identify protein tyrosine kinases of potential importance in early T cell development
Summary
Response Modifiers Program, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702, the Departments of ftEndocrinology and ~~Pathology, University of Chicago, Chicago, Illinois 60637, the. The control of phosphorylation by protein tyrosine kinases represents an important regulatory mechanism in T cell growth, function, and differentiation. Rlk represents a novel cytoplasmic tyrosine kinase with potential functions in intrathymic T cell development and mature T cell signaling. The regulation of protein tyrosine phosphorylation is a critical component of signal transduction during cell growth and differentiation. This is well illustrated in lymphocytes, where the initiation of signaling through antigen receptors is associated with the rapid tyrosine phosphorylation of multiple intracellular substrates [1,2,3]. A third cytoplasmic protein tyrosine kinase with expression restricted to the T cell lineage, ZAP-70, rapidly associates via its two SH2 domains with tyrosine-phosphorylated antigen recog-.
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