ER export signals mediate plasma membrane localization of transmembrane protein TMEM72

Transmembrane protein 72 (TMEM72) is involved in normal kidney development and tumorigenesis in renal cell carcinoma. However, the function of TMEM72 has not been experimentally examined; therefore, the role of TMEM72 is incompletely understood. In this study, we initially demonstrated that TMEM72 has four transmembrane domains (TMDs) and a long C-terminal tail. Immunofluorescence analysis showed that TMEM72 is localized on the plasma membrane but not on the outer mitochondrial membrane. Experiments performed with a series of TMEM72 deletion mutants and an evaluation of the unfolded protein response indicated that these TMDs are needed for proper protein folding or assembly. In contrast, domain-specific replacement analysis indicated the essential role of the C-terminal region of TMEM72 in protein transport. Spatial colocalization and immunoprecipitation assays showed that the proximal C-terminal region is responsible for anterograde protein transport. An amino acid sequence analysis and an immunocytochemical evaluation revealed that KRKKRKAAPEVLA, which corresponds to amino acid positions 132-144 in TMEM72, participates in efficient cellular transport. The motifs 132KRKKRK137 and 139APEVLA144 are associated with COPII and are considered to cooperate with membrane trafficking. Because efficient membrane trafficking is crucial for cells to maintain normal function, our data may contribute to elucidating the pathogenesis of membrane trafficking-associated diseases, particularly renal carcinoma and chronic kidney disease.