Futagami Taiki, Nakao Seiki, Kido Yayoi, Oka Takuji, Kajiwara Yasuhiro, Takashita Hideharu, Omori Toshiro, Furukawa Kensuke, Goto Masatoshi
Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka, Japan.
Eukaryot Cell. 2011 Nov;10(11):1504-15. doi: 10.1128/EC.05080-11. Epub 2011 Sep 16.
Wsc proteins have been identified in fungi and are believed to be stress sensors in the cell wall integrity (CWI) signaling pathway. In this study, we characterized the sensor orthologs WscA and WscB in Aspergillus nidulans. Using hemagglutinin-tagged WscA and WscB, we showed both Wsc proteins to be N- and O-glycosylated and localized in the cell wall and membrane, implying that they are potential cell surface sensors. The wscA disruptant (ΔwscA) strain was characterized by reduced colony and conidia formation and a high frequency of swollen hyphae under hypo-osmotic conditions. The deficient phenotype of the ΔwscA strain was facilitated by acidification, but not by alkalization or antifungal agents. In contrast, osmotic stabilization restored the normal phenotype in the ΔwscA strain. A similar inhibition was observed in the wscB disruptant strain, but to a lesser extent. In addition, a double wscA and wscB disruptant (ΔwscA ΔwscB) strain was viable, but its growth was inhibited to a greater degree, indicating that the functions of the products of these genes are redundant. Transcription of α-1,3-glucan synthase genes (agsA and agsB) was significantly altered in the wscA disruptant strain, resulting in an increase in the amount of alkali-soluble cell wall glucan compared to that in the wild-type (wt) strain. An increase in mitogen-activated protein kinase (MpkA) phosphorylation was observed as a result of wsc disruption. Moreover, the transient transcriptional upregulation of the agsB gene via MpkA signaling was observed in the ΔwscA ΔwscB strain to the same degree as in the wt strain. These results indicate that A. nidulans Wsc proteins have a different sensing spectrum and downstream signaling pathway than those in the yeast Saccharomyces cerevisiae and that they play an important role in CWI under hypo-osmotic and acidic pH conditions.
Wsc蛋白已在真菌中被鉴定出来，并且被认为是细胞壁完整性（CWI）信号通路中的应激传感器。在本研究中，我们对构巢曲霉中的传感器直系同源物WscA和WscB进行了表征。使用带有血凝素标签的WscA和WscB，我们发现这两种Wsc蛋白都进行了N-糖基化和O-糖基化，并定位在细胞壁和细胞膜中，这意味着它们是潜在的细胞表面传感器。wscA缺失突变体（ΔwscA）菌株的特征是菌落和分生孢子形成减少，并且在低渗条件下菌丝肿胀的频率很高。ΔwscA菌株的缺陷表型通过酸化得到促进，但碱化或抗真菌剂则不能。相反，渗透稳定作用恢复了ΔwscA菌株的正常表型。在wscB缺失突变体菌株中也观察到了类似的抑制作用，但程度较轻。此外，wscA和wscB双缺失突变体（ΔwscA ΔwscB）菌株是有活力的，但其生长受到更大程度的抑制，这表明这些基因产物的功能是冗余的。与野生型（wt）菌株相比，wscA缺失突变体菌株中α-1,3-葡聚糖合酶基因（agsA和agsB）的转录发生了显著改变，导致碱溶性细胞壁葡聚糖的量增加。由于wsc缺失，观察到丝裂原活化蛋白激酶（MpkA）磷酸化增加。此外，在ΔwscA ΔwscB菌株中观察到agsB基因通过MpkA信号传导的瞬时转录上调，其程度与wt菌株相同。这些结果表明，构巢曲霉的Wsc蛋白与酿酒酵母中的Wsc蛋白具有不同的传感谱和下游信号通路，并且它们在低渗和酸性pH条件下的CWI中发挥重要作用。
