A Yeast Genomic Screen to Identify Effectors of Kir2.1 Plasma Membrane Residence

Protein quality control is important for the disposal of toxic misfolded proteins. Ion channels represent a class of proteins that are suited for the study of protein quality control within the secretory pathway. The inward rectifying potassium channel, Kir2.1, functions at the plasma membrane in several tissues to maintain membrane potential and osmotic homeostasis, and not surprisingly defects in Kir2.1 lead to a host of diseases. To identify Kir2.1 regulators, a yeast Kir2.1 expression system was established. Although a small population appeared to localize to the plasma membrane, Kir2.1 primarily localized to the ER and a significant fraction was targeted for ER associated-degradation (ERAD). To identify the spectrum of factors that maintain Kir2.1 plasma membrane residence, the expression plasmid was introduced into a potassium transporter deficient strain in which Kir2.1 restores growth on low potassium, and the strain was crossed to the deletion collection to obtain haploid progeny. Among the mutated genes that significantly increased cell growth on low potassium were those encoding members of the Endosomal Sorting Complex Required for Transport (ESCRT). ESCRT also regulated Kir2.1 stability in HeLa cells. These data indicate that Kir2.1 function is controlled by later steps in secretory pathway quality control, but not ERAD. The screen described represents a model that can be used for other ion channels