A novel polypeptide which is useful in screening of an agent for improving insulin resistance and an agent for improving glucose metabolism, a polynucleotide encoding the polypeptide, an expression vector comprising the polynucleotide, and a cell transformed with the expression vector are disclosed. The polypeptide is a protein expressed in skeletal muscle. When the protein is overexpressed, incorporation of sugar into a cell is inhibited.A method for screening of an agent for improving insulin resistance and/or an agent for improving glucose metabolism in which the polypeptide is used, and a method for producing a pharmaceutical composition for insulin resistance and/or glucose metabolism improvement comprising a substance obtained according to the method for screening as an active ingredient are also disclosed.