1. Mlf mediates proteotoxic response via formation of cellular foci for protein folding and degradation in Giardia.
- Author
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Vinopalová, Martina, Arbonová, Lenka, Füssy, Zoltán, Dohnálek, Vít, Samad, Abdul, Bílý, Tomáš, Vancová, Marie, and Doležal, Pavel
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CELL communication , *GIARDIA lamblia , *CELL physiology , *LIFE cycles (Biology) , *MYELOID leukemia , *PROTEOLYSIS - Abstract
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. Author summary: Giardia intestinalis, a widespread intestinal parasite, has emerged as a valuable model for studying eukaryotic cell biology and host-pathogen interactions. Our study focuses on the Myeloid Leukemia Factor (Mlf) homolog in Giardia (GiMlf), an evolutionarily conserved protein with diverse cellular functions. We demonstrate that GiMlf plays a crucial role in proteostasis by forming two types of cytosolic foci: one associated with microtubular structures and Hsp40, and another comprising ubiquitin-rich, membraneless compartments near mitosomes, containing the 26S proteasome regulatory subunit. Upon cellular stress, GiMlf dynamically relocates, suggesting its involvement in the stress response. Notably, GiMlf knockout leads to extensive proteomic changes and altered encystation rates, indicating its importance in Giardia's life cycle and stress adaptation. Our findings provide insights into how Giardia, and potentially other eukaryotes, maintain proteostasis under various environmental conditions. This research enhances our understanding of fundamental parasite biology and stress response mechanisms, which are critical for pathogen survival in diverse host environments. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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