Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA.
Sci Signal. 2010 Oct 19;3(144):ra75. doi: 10.1126/scisignal.2001275.
Eukaryotic cells use multiple mitogen-activated protein kinase (MAPK) cascades to evoke appropriate responses to external stimuli. In Saccharomyces cerevisiae, the MAPK Fus3 is activated by pheromone-binding heterotrimeric guanosine triphosphate-binding protein (G protein)-coupled receptors to promote mating, whereas the MAPK Hog1 is activated by hyperosmotic stress to elicit the high-osmolarity glycerol (HOG) response. Although these MAPK pathways share several upstream components, exposure to either pheromone or osmolyte alone triggers only the appropriate response. We used fluorescence localization- and transcription-specific reporters to assess activation of these pathways in individual cells on the minute and hour time scale, respectively. Dual activation of these two MAPK pathways occurred over a broad range of stimulant concentrations and temporal regimes in wild-type cells subjected to costimulation. Thus, signaling specificity is achieved through an "insulation" mechanism, not a "cross-inhibition" mechanism. Furthermore, we showed that there was a critical period during which Hog1 activity had to occur for proper insulation of the HOG pathway.
真核细胞利用多种丝裂原激活的蛋白激酶（MAPK）级联反应来对外界刺激做出适当的响应。在酿酒酵母中，MAPK Fus3 被与 G 蛋白偶联的配体结合的异三聚体鸟苷三磷酸结合蛋白（G 蛋白）激活，以促进交配，而 MAPK Hog1 则被高渗胁迫激活，引发高渗透压甘油（HOG）反应。尽管这些 MAPK 途径共享几个上游成分，但单独接触激素或渗透剂只会触发相应的反应。我们使用荧光定位和转录特异性报告基因分别在分钟和小时的时间尺度上评估了这些途径在单个细胞中的激活情况。在受到双重刺激的野生型细胞中，这两种 MAPK 途径的双重激活发生在广泛的刺激浓度和时间范围内。因此，信号特异性是通过“隔离”机制而不是“交叉抑制”机制实现的。此外，我们还表明，在 Hog1 活性必须发生的关键时期，HOG 途径的适当隔离。
