T cell antigen receptor-mediated activation of phospholipase C requires tyrosine phosphorylation
Article Abstract:
Working out the details of the regulation of living cells is a premier problem for modern biology. Generally many processes are involved in every regulatory process, and teasing apart the individual steps is a formidable task. In the case of the activation of T-cells by the presentation of specific antigen, it has now been possible to show that the process relies on enzymatic phosphorylation in its early stages. When T-cells are presented with antigen under appropriate circumstances, an enzyme called phospholipase C begins the hydrolysis of inositol phospholipids. These molecules then serve as messengers within the cell and initiate a multitude of events involved in the activation and proliferation of the cell. An enzyme inhibitor can be used to show that protein phosphorylation is a necessary step in the stimulating of phospholipase C. Protein phosphorylation is the adding of a phosphate group to a protein, usually on a tyrosine residue in the peptide chain. This process is thought to be one of the major methods by which cells can activate or inactivate enzymes and key proteins. Phosphorylation is a key process not only in the normal regulation of cells but in the transformation of cancer cells as well. The substance genistein inhibits the activity of tyrosine kinase, an enzyme which phosphorylates proteins. When this enzyme inhibitor is added to T-cells in quantities insufficient to directly inhibit phospholipase C, triggering the antigen receptor complex does not induce the activation of phospholipase C or the subsequent activation and proliferation of the cell. Therefore, the activation of T-cells is yet another system of cellular regulation that involves tyrosine kinase as an important enzymatic step. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Science
Subject: Science and technology
ISSN: 0036-8075
Year: 1990
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Inhibition of T cell receptor expression and function in immature CD4+CD8+ cells by CD4
Article Abstract:
Interaction of the T cell receptor (TCR) with antigen (molecules that the immune system recognizes as foreign) is necessary for the stimulation of the T cells so that an immune response can occur. In the thymus, thymocytes mature into functional T cells. Most immature thymocytes, with the cell surface proteins CD4+CD8+, contain only low levels of TCR molecules. The TCR molecules that are present are only marginally functional as they can only transmit a slight intracellular signal (necessary for cell stimulation). It was found that the expression and function of the TCR on immature thymocytes is not intrinsically low but is actively inhibited by signals that are mediated by the CD4 molecule. If immature CD4+CD8+ thymocytes are separated from the signals mediated by CD4, there is a significant increase in the levels of TCR expressed on the cell surface and the ability of the TCR to mediate an intracellular signal so that the cells can be stimulated. It is important to identify and understand the regulatory mechanisms and function of the TCR in the thymus so that more can be understood about the immune system; ultimately this may help regulate it to better fight off disease. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Science
Subject: Science and technology
ISSN: 0036-8075
Year: 1990
User Contributions:
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