Albacar Marcel, Sacka Lenka, Calafí Carlos, Velázquez Diego, Casamayor Antonio, Ariño Joaquín, Zimmermannova Olga
Institut de Biotecnologia i Biomedicina & Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain.
Laboratory of Membrane Transport, Institute of Physiology of the Czech Academy of Sciences, 142220 Prague, Czech Republic.
J Fungi (Basel). 2021 Nov 25;7(12):1010. doi: 10.3390/jof7121010.
The alteration of the fine-tuned balance of phospho/dephosphorylation reactions in the cell often results in functional disturbance. In the yeast , the overexpression of Ser/Thr phosphatase Ppz1 drastically blocks cell proliferation, with a profound change in the transcriptomic and phosphoproteomic profiles. While the deleterious effect on growth likely derives from the alteration of multiple targets, the precise mechanisms are still obscure. Ppz1 is a negative effector of potassium influx. However, we show that the toxic effect of Ppz1 overexpression is unrelated to the Trk1/2 high-affinity potassium importers. Cells overexpressing Ppz1 exhibit decreased K content, increased cytosolic acidification, and fail to properly acidify the medium. These effects, as well as the growth defect, are counteracted by the deletion of gene, which encodes a plasma membrane Na, K/H antiporter. The beneficial effect of a lack of Nha1 on the growth vanishes as the pH of the medium approaches neutrality, is not eliminated by the expression of two non-functional Nha1 variants (D145N or D177N), and is exacerbated by a hyperactive Nha1 version (S481A). All our results show that high levels of Ppz1 overactivate Nha1, leading to an excessive entry of H and efflux of K, which is detrimental for growth.
细胞中磷酸化/去磷酸化反应的微调平衡发生改变通常会导致功能紊乱。在酵母中，丝氨酸/苏氨酸磷酸酶Ppz1的过表达会严重阻碍细胞增殖，导致转录组和磷酸化蛋白质组图谱发生深刻变化。虽然对生长的有害影响可能源于多个靶点的改变，但其确切机制仍不清楚。Ppz1是钾离子内流的负效应因子。然而，我们发现Ppz1过表达的毒性作用与Trk1/2高亲和力钾离子转运体无关。过表达Ppz1的细胞钾含量降低，胞质酸化增加，且无法适当地酸化培养基。这些影响以及生长缺陷可通过缺失编码质膜钠钾/氢反向转运体的基因来抵消。随着培养基pH值接近中性，缺乏Nha1对生长的有益作用消失，两种无功能的Nha1变体（D145N或D177N）的表达并不能消除这种作用，而高活性的Nha1版本（S481A）则会加剧这种作用。我们所有的结果表明，高水平的Ppz1会过度激活Nha1，导致氢离子过度内流和钾离子外流，这对生长是有害的。
