Podszywalow-Bartnicka Paulina, Strzelecka-Kiliszek Agnieszka, Bandorowicz-Pikula Joanna, Pikula Slawomir
Department of Biochemistry, Nencki Institute of Experimental Biology, Warszawa, Poland.
Acta Biochim Pol. 2007;54(2):261-71. Epub 2007 Jun 4.
Annexin A6 (AnxA6) is a Ca(2+)-dependent membrane-binding protein involved in vesicular traffic. The likely participation of AnxA6 in the response of lymphocytes to Ca(2+) signals has not been investigated yet. The present study focuses on intracellular relocation of AnxA6 in human Jurkat T lymphoblasts upon stimulation followed by transient increase of intracellular [Ca(2+)] and exocytosis of interleukin-2 (IL-2). Stimulation of the cells under different experimental conditions (by lowering pH and/or by rising extracellular [Ca(2+)] in the presence of ionomycin) induced time-dependent transients of intracellular [Ca(2+)] and concomitant changes in AnxA6 intracellular localization and in IL-2 secretion, with only minor effects on cell viability and apoptosis. In resting conditions (in the presence of EGTA or with no ionophore) AnxA6 was localized uniformly in the cytosol, whereas it translocated to vesicular structures beneath the plasma membrane within 5 min following stimulation of Jurkat T cells and rise of intracellular [Ca(2+)] at pH 7.4. Lowering the extracellular pH value from 7.4 to 6.0 significantly enhanced this process. AnxA6 changed its location from the cytosol to the secretory granules and early endosomes which seem to represent membranous targets for annexin. In conclusion, AnxA6 is sensitive to variations in intracellular [Ca(2+)] upon stimulation of Jurkat T cells, as manifested by a switch in its intracellular localization from the cytosol to vesicular structures located in close proximity to the plasma membrane, suggestive of participation of AnxA6 in calcium- and proton-dependent secretion of cytokines by lymphocytes.
膜联蛋白A6（AnxA6）是一种参与囊泡运输的钙依赖性膜结合蛋白。AnxA6在淋巴细胞对钙信号反应中的可能参与尚未得到研究。本研究聚焦于人类Jurkat T淋巴母细胞在受到刺激后，细胞内[Ca(2+)]短暂升高并伴有白细胞介素-2（IL-2）胞吐作用时AnxA6的细胞内重新定位。在不同实验条件下（通过降低pH值和/或在离子霉素存在下升高细胞外[Ca(2+)]）刺激细胞，可诱导细胞内[Ca(2+)]的时间依赖性瞬变以及AnxA6细胞内定位和IL-2分泌的伴随变化，对细胞活力和凋亡仅有轻微影响。在静息状态下（存在乙二醇双四乙酸或无离子载体），AnxA6均匀地定位于细胞质中，而在pH 7.4时刺激Jurkat T细胞并使细胞内[Ca(2+)]升高后5分钟内，它会转位至质膜下方的囊泡结构。将细胞外pH值从7.4降至6.0可显著增强这一过程。AnxA6从细胞质转移至分泌颗粒和早期内体，这些似乎是膜联蛋白的膜性靶点。总之，Jurkat T细胞受到刺激时，AnxA6对细胞内[Ca(2+)]的变化敏感，表现为其细胞内定位从细胞质切换至紧邻质膜的囊泡结构，提示AnxA6参与淋巴细胞钙和质子依赖性细胞因子分泌。
