IST1

IST1 Full Name

increased sodium tolerance 1 homolog (yeast)

IST1 Introduction

In humans, the IST1 gene is located at chromosome 16q22.2, with a complete coding sequence that produces multiple transcript variants via alternative splicing, corresponding to different protein isoforms with subtle functional differences. A pseudogene of IST1 has been identified on human chromosome 19, which lacks complete protein-coding capacity and does not participate in normal cellular functional regulation. The gene is evolutionarily conserved, with homologous sequences identified in yeast, mice, and most mammalian species, indicating its essential and irreplaceable role in eukaryotic cellular life activities.

Figure 1. Structure of IST1.

Core Biological Functions of IST1
IST1 executes diverse and precise biological functions centered on membrane trafficking and ESCRT pathway regulation. First, it is an essential factor for efficient cellular cytokinesis abscission. It recruits VPS4A/VPS4B ATPases to the midbody of dividing cells, facilitating membrane separation in the final stage of cell division, while it is dispensable for HIV-1 budding, showing functional specificity in membrane scission events. Second, IST1 selectively regulates endocytic recycling pathways. The depletion of IST1 significantly impairs the transport of transferrin receptor from early/sorting endosomes to the endocytic recycling compartment, and promotes the rapid recycling of peripheral endosome cargos to the plasma membrane. It also participates in the export and sorting of mannose 6-phosphate receptor from early endosomes, maintaining the normal circulation and distribution of intracellular membrane proteins. Moreover, IST1 participates in the multivesicular body (MVB) sorting pathway and regulates the recycling of plasma membrane transporters. In yeast, it modulates the membrane recycling of arginine transporters and affects cellular sodium tolerance, revealing its conserved regulatory role in substance transport and stress adaptation across species.

Protein Interaction Mechanisms of IST1
IST1 exerts its biological functions mainly through MIM-MIT domain-mediated protein interactions. Its classic binding partners include the ATPase VPS4, ESCRT-III subunit CHMP1, regulatory protein LIP5, and sorting nexin SNX1. It also forms a stable complex with Did2, another ESCRT-III accessory protein, to jointly regulate ESCRT-III polymer disassembly.
Notably, IST1 shows a concentration-dependent dual regulatory mechanism on ESCRT-III disassembly: low concentrations of IST1 activate VPS4-mediated ESCRT-III complex dissociation from membranes, while high concentrations exert a strong inhibitory effect, forming a precise negative feedback regulatory loop to prevent excessive or insufficient disassembly of the ESCRT complex and ensure the accuracy of membrane trafficking processes.

Alternate Names for IST1

IST1; increased sodium tolerance 1 homolog (yeast); KIAA0174; IST1 homolog; hIST1; increased sodium tolerance-1; putative MAPK-activating protein PM28; MGC117220;