Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.
Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, 142 20 Prague 4, Czech Republic.
Mol Biol Cell. 2023 Jun 1;34(7):ar66. doi: 10.1091/mbc.E22-06-0222. Epub 2023 Mar 29.
Unc-51-like kinase (ULK) family serine-threonine protein kinase homologues have been linked to the function of motile cilia in diverse species. Mutations in Fused/STK36 and ULK4 in mice resulted in hydrocephalus and other phenotypes consistent with ciliary defects. How either protein contributes to the assembly and function of motile cilia is not well understood. Here we studied the phenotypes of and gene knockout (KO) mutants in the flagellated protist . Both KO mutants exhibited a variety of structural defects of the flagellum cytoskeleton. Biochemical approaches indicate spatial proximity of these proteins and indicate a direct interaction between the N-terminus of LmxULK4 and LmxFused. Both proteins display a dispersed localization throughout the cell body and flagellum, with enrichment near the flagellar base and tip. The stable expression of LmxULK4 was dependent on the presence of LmxFused. Fused/STK36 was previously shown to localize to mammalian motile cilia, and we demonstrate here that ULK4 also localizes to the motile cilia in mouse ependymal cells. Taken together these data suggest a model where the pseudokinase ULK4 is a positive regulator of the kinase Fused/ STK36 in a pathway required for stable assembly of motile cilia.
UNC-51 样激酶 (ULK) 家族丝氨酸-苏氨酸蛋白激酶同源物与多种物种的运动纤毛功能有关。在小鼠中，Fused/STK36 和 ULK4 的突变导致脑积水和其他与纤毛缺陷一致的表型。这两种蛋白如何有助于运动纤毛的组装和功能尚不清楚。在这里，我们研究了有鞭毛原生生物中的 和 基因敲除 (KO) 突变体的表型。这两种 KO 突变体都表现出鞭毛细胞骨架的各种结构缺陷。生化方法表明这些蛋白质的空间接近性，并表明 LmxULK4 的 N 端与 LmxFused 之间存在直接相互作用。这两种蛋白质在整个细胞体和鞭毛中均呈现弥散性定位，在鞭毛基部和顶端附近富集。LmxULK4 的稳定表达依赖于 LmxFused 的存在。Fused/STK36 先前被证明定位于哺乳动物运动纤毛，我们在此证明 ULK4 也定位于小鼠室管膜细胞中的运动纤毛。这些数据表明，在运动纤毛稳定组装所需的途径中，假激酶 ULK4 是激酶 Fused/STK36 的正调节剂。
