Moon Owen R, Newman Andrew C, Alanazi Abdullah S, Wehenkel Sophie C, Gawel-Bęben Katarzyna, Ivetic Aleksandar, Price David A, Knäuper Vera, Ager Ann
Division of Infection and Immunity, School of Medicine, Cardiff University, Cardiff, UK.
School of Dentistry, Cardiff University, Cardiff, UK.
J Biol Chem. 2025 Jul 10;301(8):110473. doi: 10.1016/j.jbc.2025.110473.
Leucocyte (L)-selectin is essential for mounting protective immunity to pathogens. As well as regulating leucocyte recruitment, it also regulates their activation and differentiation inside tissues thereby shaping local immune responses. The biochemical signals that regulate these diverse functions of L-selectin are poorly understood. Leucocyte activation induces proteolytic shedding of L-selectin ectodomain (ECD) but the impact of ECD shedding on signaling downstream of L-selectin is not known. In T cells, there is substantial overlap between signaling downstream of L-selectin and the T-cell receptor (TCR). Cross-linking of L-selectin stimulates phosphorylation of the cytoplasmic tail and forward signaling via the nonreceptor tyrosine kinases Lck and Zap70. Cross-linking of TCR induces phosphorylation-dependent binding of PKC isozymes to L-selectin cytoplasmic tail and PKCα-dependent shedding of ECD. To further understand the role of L-selectin in T cell biology, we used T cells to dissect the cross-talk between L-selectin and physiological TCR activation. We used a combination of imaging flow cytometry and biochemistry to localize L-selectin ECD and intracellular domain (ICD) following engagement of the TCR. We show that following A Metalloproteinase And Disintegrin (ADAM) 17-dependent ECD shedding from the plasma membrane, the ICD-containing transmembrane retained fragment undergoes intramembrane proteolysis by PS1-containing γ-secretase. Subsequent degradation of L-selectin ICD occurs via the proteasome in the vicinity of the plasma membrane. Regulated intramembrane proteolysis and rapid degradation of L-selectin ICD following TCR activation suggests that the turnover of L-selectin cytoplasmic tail is an important regulator of T-cell costimulation by L-selectin.
白细胞（L）-选择素对于抵御病原体的保护性免疫至关重要。除了调节白细胞募集外，它还调节白细胞在组织内的激活和分化，从而塑造局部免疫反应。调节L-选择素这些多样功能的生化信号尚不清楚。白细胞激活会诱导L-选择素胞外域（ECD）的蛋白水解性脱落，但ECD脱落对L-选择素下游信号传导的影响尚不清楚。在T细胞中，L-选择素下游信号传导与T细胞受体（TCR）之间存在大量重叠。L-选择素的交联刺激细胞质尾部的磷酸化，并通过非受体酪氨酸激酶Lck和Zap70进行正向信号传导。TCR的交联诱导PKC同工酶与L-选择素细胞质尾部的磷酸化依赖性结合以及PKCα依赖性的ECD脱落。为了进一步了解L-选择素在T细胞生物学中的作用，我们使用T细胞来剖析L-选择素与生理性TCR激活之间的相互作用。我们结合成像流式细胞术和生物化学方法，在TCR激活后定位L-选择素ECD和细胞内结构域（ICD）。我们发现，在血浆膜上发生金属蛋白酶和去整合素（ADAM）17依赖性的ECD脱落后，含有ICD的跨膜保留片段会被含PS1的γ-分泌酶进行膜内蛋白水解。随后，L-选择素ICD在血浆膜附近通过蛋白酶体降解。TCR激活后L-选择素ICD的受调控膜内蛋白水解和快速降解表明，L-选择素细胞质尾部的周转是L-选择素对T细胞共刺激的重要调节因子。
