NOVEL REDISTRIBUTION OF AN INTRACELLULAR POOL OF CD45 ACCOMPANIES T-CELL ACTIVATION

The major tyrosine phosphatase activity against angiotensin detected in membranes of the antigen-specific T cell hybridoma 2B4 is contained in the cytoplasmic tail of the CD45 molecule. When these cells are stimulated with either an antibody directed against the T cell antigen receptor or an activating anti-Thy-1 antibody, there is a rapid redistribution of CD45 in the cells. The redistribution can be observed in two ways: morphology and subcellular fractionation. Morphologic examination of resting cells reveals intense CD45 staining of the Golgi as well as surface staining. Upon activation the Golgi is rapidly cleared of CD45. This redistribution is specific for CD45 and is not observed for an intrinsic Golgi protein, mannosidase II, or a protein traversing the secretory pathway, the T cell receptor. In activated cells, in contrast to resting cells, approximately 30% of the total cellular CD45 is precipitated either at 280 x g or at 200,000 x g through a 2.2 M sucrose cushion after cell homogenization. This fraction is not accessible to cell surface labeling. CD45 redistribution does not require hydrolysis of phosphatidylinositides and cannot be reproduced by the addition of phorbol ester and calcium ionophore. It does require the presence of an intact functional T cell receptor on the cell surface. These studies suggest that the residence time of CD45 within an intracellular organelle can be acutely regulated by a signal mediated via the T cell receptor. This regulation may control access of this phosphatase to critical substrates.