Department of Parasitology, Faculty of Science, Charles University, BIOCEV, Prague, Czech Republic.
Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, United States of America.
PLoS Pathog. 2024 Oct 21;20(10):e1012617. doi: 10.1371/journal.ppat.1012617. eCollection 2024 Oct.
Myeloid leukemia factor 1 (Mlf1) was identified as a proto-oncoprotein that affects hematopoietic differentiation in humans. However, its cellular function remains elusive, spanning roles from cell cycle regulation to modulation of protein aggregate formation and participation in ciliogenesis. Given that structurally conserved homologs of Mlf1 can be found across the eukaryotic tree of life, we decided to characterize its cellular role underlying this phenotypic pleiotropy. Using a model of the unicellular eukaryote Giardia intestinalis, we demonstrate that its Mlf1 homolog (GiMlf) mainly localizes to two types of cytosolic foci: microtubular structures, where it interacts with Hsp40, and ubiquitin-rich, membraneless compartments, found adjacent to mitochondrion-related organelles known as mitosomes, containing the 26S proteasome regulatory subunit 4. Upon cellular stress, GiMlf either relocates to the affected compartment or disperses across the cytoplasm, subsequently accumulating into enlarged foci during the recovery phase. In vitro assays suggest that GiMlf can be recruited to membranes through its affinity for signaling phospholipids. Importantly, cytosolic foci diminish in the gimlf knockout strain, which exhibits extensive proteomic changes indicative of compromised proteostasis. Consistent with data from other cellular systems, we propose that Mlf acts in the response to proteotoxic stress by mediating the formation of function-specific foci for protein folding and degradation.
髓系白血病因子 1（Mlf1）被鉴定为一种原癌蛋白，影响人类造血分化。然而，其细胞功能仍然难以捉摸，涵盖了从细胞周期调控到调节蛋白质聚集体形成和参与纤毛发生的作用。鉴于 Mlf1 的结构保守同源物可以在真核生物的生命之树上找到，我们决定描述其在这种表型多效性下的细胞作用。使用单细胞真核生物贾第虫的模型，我们证明其 Mlf1 同源物（GiMlf）主要定位于两种类型的细胞质焦点：微管结构，其中它与 Hsp40 相互作用，以及富含泛素的无膜隔室，位于与称为线粒体相关细胞器相邻的位置mitosomes，其中包含 26S 蛋白酶体调节亚基 4。在细胞应激下，GiMlf 要么重新定位到受影响的隔室，要么散布在细胞质中，随后在恢复阶段积累成大焦点。体外测定表明，GiMlf 可以通过其对信号磷脂的亲和力被招募到膜上。重要的是，在 gimlf 敲除株中，细胞质焦点减少，该株表现出广泛的蛋白质组变化，表明蛋白质稳态受损。与来自其他细胞系统的数据一致，我们提出 Mlf 通过介导特定于功能的焦点形成来参与蛋白质折叠和降解，以响应蛋白毒性应激。
