Overexpression of AE1 Prague, but not of AE1 SAO, inhibits wild-type AE1 trafficking in Xenopus oocytes

Abstract

Mutations in the AE1 (band 3) anion exchanger of human erythrocytes have been associated with altered red cell shape and heritable disease. The Southeast Asian Ovalocytosis (SAO) AE1 mutation, a 27 nt deletion producing the delta 400-408 form of AE1, and the AE1 Prague mutation, a 10 nt insertion producing a frameshift after AE1 aa 821 leading to premature termination, are found only in the heterozygous state. We therefore examined accumulation and function of wt AE1 polypeptide in Xenopus oocytes when coexpressed with AE1 SAO and with AE1 Prague. Our SAO construct lacked the K56E (AE1 Memphis) polymorphism present in the endogenous AE1 SAO protein. Neither mutant AE1 mediated Cl- uptake into cRNA-injected Xenopus oocytes. Coinjection of mutant and wt cRNAs led to dose-dependent inhibition of wt function by AE1 Prague, but not by SAO. Though in vitro translation of the two mutants revealed little difference in their insertion into microsomal membranes, AE1 Prague accumulated in Xenopus oocytes to lower levels than did AE1 SAO or wt. Unlike AE1 SAO polypeptide, AE1 Prague polypeptide was not detectable at the oocyte surface. Moreover, overexpression of AE1 Prague, in contrast to AE1 SAO, reduced the accumulation of wt AE1, at the oocyte surface. This inhibition occurred in the absence of detectable heteromer formation between the AE1 Prague and wt AE1 polypeptides.