Schenk P W, Nebl T, Fisher P R, Snaar-Jagalska B E
Section of Cell Biology, Institute of Molecular Plant Sciences, Leiden University, Leiden, 2300 RA, The Netherlands.
Biochem Biophys Res Commun. 1999 Jul 5;260(2):504-9. doi: 10.1006/bbrc.1999.0862.
Ca(2+) influx and mitogen-activated protein (MAP) kinase activation are important phenomena in signal transduction, which are often interconnected. We investigated whether serpentine receptor-dependent, Gbeta-independent activation of MAP kinase ERK2 by chemoattractant cyclic AMP (cAMP) is mediated by Ca(2+) influx in the social amoeba Dictyostelium discoideum. We generated a D. discoideum double mutant, which harbours a temperature-sensitive Gbeta subunit and expresses the apoaequorin protein. Utilizing this mutant, we demonstrate that cAMP induced Ca(2+) influx into intact D. discoideum cells can be blocked completely at both the permissive and the restrictive temperature, by using either gadolinium ions or Ruthenium Red. Under the same experimental conditions, these substances do not abolish cAMP stimulation of ERK2 at either temperature. We conclude that there is a Gbeta- and Ca(2+) influx-independent pathway for the receptor-dependent activation of MAP kinase ERK2 in D. discoideum.
钙离子内流和丝裂原活化蛋白（MAP）激酶激活是信号转导中的重要现象，二者常常相互关联。我们研究了趋化性环磷酸腺苷（cAMP）对社会变形虫盘基网柄菌中MAP激酶ERK2的蛇形受体依赖性、Gβ非依赖性激活是否由钙离子内流介导。我们构建了一个盘基网柄菌双突变体，其含有一个温度敏感型Gβ亚基并表达脱辅基水母发光蛋白。利用该突变体，我们证明，通过使用钆离子或钌红，在允许温度和限制温度下，cAMP诱导的钙离子内流均可完全阻断进入完整的盘基网柄菌细胞。在相同实验条件下，这些物质在任一温度下均不会消除cAMP对ERK2的刺激。我们得出结论，在盘基网柄菌中，存在一条不依赖Gβ和钙离子内流的途径来实现受体依赖性的MAP激酶ERK2激活。
