Human erythroid band 3 "anion exchanger 1" is expressed in transformed lymphocytes

The anion transporter, band 3, is a ubiquitous protein. It is present in brain and all other tissues examined. Not only is band 3 present in cell membranes, but also in nuclear, Golgi and mitochondria membranes. There are four isoforms of band 3, the anion exchanger (AE) proteins, thus far discovered. They are products of different genes. Lymphocytes are reported to contain AE2, but not AE1. We hypothesized that induction or up-regulation of AE1 occurs when lymphocytes are transformed as an initial event in the path to malignancy. We transformed lymphocytes containing a single base mutation with Epstein Barr Virus (EBV). The mutation of band 3, high transport band 3 (HTbd3), exhibits anion transport that is 2-3 times normal in erythrocytes which contain AE1. This facilitated our identification of AE1 since the probability that 2 different gene products would have the same mutation approaches zero. Thus, we have a base mutation in addition to linear sequence to identify AE1. A 133 base pair (bp) fragment including the affected region was amplified from the mRNA of lymphocytes from the HTbd3 mutant. AE1 primers were used to amplify regions of interest. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to generate cDNA which was sequenced. The sequence of the crucial 133 base pair segment from high transport lymphocytes was 100% identical to the sequence published for the red blood cell band 3 of the same mutant. As reported previously for erythrocytes, this mutation is a C-->T base change which changes a proline to leucine in the protein sequence. Restriction enzyme digests of AE1 cDNA from normal and HTBD3 lymphocytes confirmed that the proposita was homozygous for the mutation, and showed the father to be heterozygous. Anion transport was increased in HTbd3 EBV transformed lymphocytes, as was the case with HTbd3 erythrocytes. AE2 was identified in lymphocytes by sequence. Thus, EBV transformed lymphocytes express the erythroid band 3 (AE1) in addition to AE2.