Argonaute 2 Silencing of Band 3 in Early Reticulocytes

Post-transcriptional gene silencing by RNA-induced silencing complex (RISC) in erythropoiesis is a rapidly evolving field of study. Disruption of microRNA (miRNA) synthesis has been shown to hinder erythropoiesis and has been linked to disease. The presence of miRNA in circulating RBCs has recently been reported; however, clear understanding of their role and effectors has yet to be determined.

In this study, freshly drawn RBC were density separated on discontinuous percoll gradients. The top two fractions, fraction 1 (F1) representative of the top layer containing the youngest, reticulocyte-like cells, and a second fraction with greater density and non-reticulocyte properties (F2), were isolated. Cell populations were analyzed to compare RBC protein levels using western blotting (WB). qRT-PCR was used to evaluate band 3 RNA. Argonaute (AGO2) RNA immunoprecipitation (RIP), was used to ascertain RISC mediated transcriptional repression of band 3 using qRT-PCR.

Band 3 protein expression was elevated in the denser F2 compared to F1, in freshly drawn normal RBCs. RNA levels of band 3 complemented protein levels, as increased band 3 RNA was observed in F2. RIP experiments revealed elevated post-transcriptional control of band 3 through increased association of its RNA with AGO2 in F1 compared to F2 thereby, correlating with greatly reduced, sometimes undetectable protein levels of band 3 in F1.

We confirm the presence of AGO2 in circulating RBCs. We report, for the first time, the post-transcriptional control of band 3, an integral RBC transmembrane protein, in circulating reticulocyte-like cells. These results suggest a possible subpopulation of reticulocytes, a pro-reticulocyte, with ongoing control of band 3 expression following enucleation, and a potential role of miRNA-RISC in band 3 pathology.