Dietrich J, Bäckström T, Lauritsen J P, Kastrup J, Christensen M D, von Bülow F, Palmer E, Geisler C
Institute of Medical Microbiology and Immunology, University of Copenhagen, The Panum Institute, Building 18.3, Blegdamsvej 3C, DK-2200 Copenhagen, Denmark.
J Biol Chem. 1998 Sep 11;273(37):24232-8. doi: 10.1074/jbc.273.37.24232.
The T cell receptor (TCR) is internalized following activation of protein kinase C (PKC) via a leucine (Leu)-based motif in CD3gamma. Some studies have indicated that the TCR is recycled back to the cell surface following PKC-mediated internalization. The functional state of recycled TCR and the mechanisms involved in the sorting events following PKC-induced internalization are not known. In this study, we demonstrated that following PKC-induced internalization, the TCR is recycled back to the cell surface in a functional state. TCR recycling was dependent on dephosphorylation of CD3gamma, probably mediated by the serine/threonine protein phosphatase-2A, but independent on microtubules or actin polymerization. Furthermore, in contrast to ligand-mediated TCR sorting, recycling of the TCR was independent of the tyrosine phosphatase CD45 and the Src tyrosine kinases p56(Lck) and p59(Fyn). Studies of mutated TCR and chimeric CD4-CD3gamma molecules demonstrated that CD3gamma did not contain a recycling signal in itself. In contrast, the only sorting information in CD3gamma was the Leu-based motif that mediated lysosomal sorting of chimeric CD4-CD3gamma molecules. Finally, we found a correlation between the phosphorylation state of CD3gamma and T cell responsiveness. Based on these observations a physiological role of CD3gamma and TCR cycling is proposed.
T细胞受体（TCR）在蛋白激酶C（PKC）通过CD3γ中基于亮氨酸（Leu）的基序激活后被内化。一些研究表明，TCR在PKC介导的内化后会循环回到细胞表面。循环TCR的功能状态以及PKC诱导内化后分选事件所涉及的机制尚不清楚。在本研究中，我们证明，在PKC诱导内化后，TCR以功能状态循环回到细胞表面。TCR循环依赖于CD3γ的去磷酸化，可能由丝氨酸/苏氨酸蛋白磷酸酶-2A介导，但不依赖于微管或肌动蛋白聚合。此外，与配体介导的TCR分选不同，TCR的循环不依赖于酪氨酸磷酸酶CD45以及Src酪氨酸激酶p56（Lck）和p59（Fyn）。对突变TCR和嵌合CD4-CD3γ分子的研究表明，CD3γ本身不包含循环信号。相反，CD3γ中唯一的分选信息是介导嵌合CD4-CD3γ分子溶酶体分选的基于Leu的基序。最后，我们发现CD3γ的磷酸化状态与T细胞反应性之间存在相关性。基于这些观察结果，我们提出了CD3γ和TCR循环的生理作用。
