Robertson Leslie K, Mireau Laura R, Ostergaard Hanne L
Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada.
J Immunol. 2005 Dec 15;175(12):8138-45. doi: 10.4049/jimmunol.175.12.8138.
PI3K is an important regulator of a number of cellular processes. We examined the contribution of PI3K to mouse CTL signaling, leading to degranulation. We show that TCR-triggered, but not phorbol ester and calcium ionophore-induced, CTL degranulation is dependent on PI3K activity. Although PI3K activity is required for optimal LFA-1-mediated adhesion and cell spreading, this most likely does not account for its full contribution to degranulation. We demonstrate that PI3K is required for TCR-stimulated ERK activation in CTL, which we have shown previously to be required for CTL degranulation. We thus define a pathway through which PI3K most likely regulates degranulation and in which ERK appears to be a key signaling molecule. Furthermore, we identified the cytoskeletal adaptor paxillin as a target of ERK downstream of TCR stimulation. Consistent with a role in degranulation, we demonstrate that paxillin is localized to the microtubule organizing center in resting cells and upon target cell binding is recruited to the contact point with the target cell. These studies demonstrate that PI3K regulates ERK activity leading to CTL degranulation, and identify paxillin as a target of ERK downstream of the TCR. That paxillin is independently phosphorylated by both tyrosine kinase(s) and ERK downstream of the TCR and localized both at the microtubule organizing center and at the target cell contact point suggests an important role for paxillin in CTL-mediated killing.
磷脂酰肌醇-3激酶（PI3K）是多种细胞过程的重要调节因子。我们研究了PI3K对小鼠细胞毒性T淋巴细胞（CTL）信号传导的作用，该信号传导可导致脱颗粒。我们发现，TCR触发的CTL脱颗粒依赖于PI3K活性，而佛波酯和钙离子载体诱导的脱颗粒则不依赖于PI3K活性。虽然PI3K活性对于LFA-1介导的最佳黏附及细胞铺展是必需的，但这很可能无法完全解释其对脱颗粒的作用。我们证明，PI3K是CTL中TCR刺激的细胞外信号调节激酶（ERK）激活所必需的，我们之前已表明ERK激活对于CTL脱颗粒是必需的。因此，我们确定了一条PI3K最有可能调节脱颗粒的途径，其中ERK似乎是关键的信号分子。此外，我们确定细胞骨架衔接蛋白桩蛋白是TCR刺激下游ERK的靶点。与在脱颗粒中的作用一致，我们证明桩蛋白在静息细胞中定位于微管组织中心，在与靶细胞结合后被招募至与靶细胞的接触点。这些研究表明，PI3K调节ERK活性从而导致CTL脱颗粒，并确定桩蛋白是TCR下游ERK的靶点。桩蛋白在TCR下游被酪氨酸激酶和ERK独立磷酸化，并定位于微管组织中心和靶细胞接触点，这表明桩蛋白在CTL介导的杀伤中起重要作用。
