Qin S, Minami Y, Hibi M, Kurosaki T, Yamamura H
Department of Biochemistry, Kobe University School of Medicine, Kobe 650, Japan.
J Biol Chem. 1997 Jan 24;272(4):2098-103. doi: 10.1074/jbc.272.4.2098.
It was found that Syk protein-tyrosine kinase is rapidly activated in B cells after H2O2 treatment (oxidative stress) or increased extracellular NaCl concentration (osmotic stress) as well as in response to B cell receptor activation. In this study we examined the involvement of Syk in responses elicited by these types of extracellular stress, particularly Ca2+ responses and c-Jun amino-terminal kinase (JNK) activation, using a chicken B cell line, DT40, as well as the DT40-derived mutant DT40/Syk(-), which does not express Syk. Osmotic stress evokes increases in [Ca2+]i by stimulating an extracellular Ca2+ influx in both DT40 and DT40/Syk(-) cells. In comparison, oxidative stress elicits an increase in [Ca2+]i by stimulating both an extracellular Ca2+ influx and Ca2+ release from internal stores in DT40 cells, but this Ca2+ response is partially abolished in DT40/Syk(-) cells, indicating that the oxidative stress-induced Ca2+ response is at least partly dependent on Syk. Interestingly, the depletion of Ca2+ results in a significantly decreased level of Syk activation in DT40 cells stimulated by oxidative but not osmotic stress. Furthermore, JNK is activated to different extents by these two types of stress. The extent of JNK activation in DT40/Syk(-) cells in response to osmotic stress is comparable to that observed in DT40 cells. Intriguingly, oxidative stress-induced JNK activation is significantly compromised in DT40/Syk(-) cells. Collectively, these results indicate that both the Ca2+ response and JNK activity induced by oxidative stress are partly dependent on Syk, whereas those induced by osmotic stress are independent of Syk.
研究发现，在H2O2处理（氧化应激）、细胞外NaCl浓度升高（渗透应激）后，以及响应B细胞受体激活时，Syk蛋白酪氨酸激酶在B细胞中会迅速被激活。在本研究中，我们使用鸡B细胞系DT40以及不表达Syk的DT40衍生突变体DT40/Syk(-)，研究了Syk在这些类型的细胞外应激引发的反应中的作用，特别是Ca2+反应和c-Jun氨基末端激酶（JNK）激活。渗透应激通过刺激DT40和DT40/Syk(-)细胞的细胞外Ca2+内流，引起细胞内Ca2+浓度（[Ca2+]i）升高。相比之下，氧化应激通过刺激DT40细胞的细胞外Ca2+内流和细胞内钙库释放Ca2+，引起[Ca2+]i升高，但这种Ca2+反应在DT40/Syk(-)细胞中部分被消除，这表明氧化应激诱导的Ca2+反应至少部分依赖于Syk。有趣的是，在氧化应激而非渗透应激刺激的DT40细胞中，Ca2+的消耗导致Syk激活水平显著降低。此外，这两种应激对JNK的激活程度不同。DT40/Syk(-)细胞对渗透应激的JNK激活程度与DT40细胞中观察到的相当。有趣的是，氧化应激诱导的JNK激活在DT40/Syk(-)细胞中显著受损。总体而言，这些结果表明，氧化应激诱导的Ca2+反应和JNK活性部分依赖于Syk，而渗透应激诱导的则与Syk无关。
