While the C-terminal cytoplasmic tail of anion exchanger 1 (AE1, band 3) has been reported to possess important physiological roles, including one for proper membrane trafficking, its precise characteristics remain unclear. To clarify the overall structural consequences of the conserved sequence EL(K/Q)(L/C)LD(A/G)DD, containing the core binding sequence LDADD for carbonic anhydrase II, in the C-terminal region, we analyzed the membrane expression and turnover of bovine AE1 with a series of truncation and substitution mutations in HEK293 cells. Immunofluorescence microscopy and cell-surface biotinylation demonstrated that truncation mutants missing 18 C-terminal residues targeted the plasma membrane, but the one lacking the conserved region, by truncation of 28 amino acid residues, was retained inside the cells. Substitutions of Ala for Glusup(901), Leusup(902), Leusup(905), and Aspsup(906) in the sequence E901L(K/Q)(L/C)LDADD909 of bovine AE1 or those in the corresponding murine sequence also caused intracellular retention, though these mutants had half-lives comparable to that for wild-type AE1. These data demonstrate that the conserved amino acid residues Glusup(1), Leusup(2), Leusup(5), and Aspsup(6) in the EL(K/Q)(L/C)LD(A/G)DD region have essential structural consequences in stable expression of AE1 at the plasma membrane regardless of the ability in binding to carbonic anhydrase II of this region.

To characterize the roles of C-peptide in vascular homeostatic processes, we examined the genes regulated by C-peptide in LEII mouse lung microvascular endothelial cells. Treatment of the cells with C-peptide increased the expression of c-Jun N-terminal kinase 1 (JNK1) mRNA dose-dependently, accompanied by an increase in JNK1 protein content. Prior treatment of the cells with PD98059, an ERK kinase inhibitor or SB203580, a p38MAPK inhibitor, abrogated the C-peptide-elicited JNK1 mRNA expression. These results indicate that C-peptide increases JNK1 protein levels, possibly through ERK- and p38MAPK-dependent activation of JNK gene transcription.