A novel erythroid anion exchange variant (Gly796Arg) of hereditary stomatocytosis associated with dyserythropoiesis

Abstract

Background \ud \ud Stomatocytoses are a group of inherited autosomal dominant hemolytic anemias and include overhydrated hereditary stomatocytosis, dehydrated hereditary stomatocytosis, hereditary cryohydrocytosis and familial pseudohyperkalemia. \ud \ud Design and Methods \ud \ud We report a novel variant of hereditary stomatocytosis clue to a de novo band 3 mutation (p. G796R-band3 CEINGE) associated with a dyserythropoietic phenotype. Band 3 genomic analysis, measurement at of hematologic parameters and red cell indices and morphological analysis of bone marrow were carried out. We then evaluated the red cell membrane permeability and ion transport systems by functional studies of the patients erythrocytes and Xenopus oocytes transfected with mutated band 3. We analyzed the red cell membrane tyrosine phosphorylation profile and the membrane association of the tyrosine kinases Syk and Lyn from the Src-family-kinase group, since the activity of the membrane cation transport pathways is related to cyclic phosphorylation-dephosphorylation events. \ud \ud Results \ud \ud The patient showed mild hemolytic anemia with circulating stomatocytes together with signs of dyserythropoiesis. Her red cells displayed increased Na(+) content with decreased K(+) content and abnormal membrane cation transport activities. Functional characterization of band 3 CEINGE in Xenopus oocytes showed that the mutated band 3 is converted from being an anion exchanger (Cl(-), HCO(3)(-)) to being a cation pathway for Na(+) and K(+). Increased tyrosine phosphorylation of some red cell membrane proteins was observed in diseased erythrocytes. Syk and Lyn membrane association was increased in the patient's red cells compared to in normal controls, indicating perturbation of phospho-signaling pathways involved in cell volume regulation events. \ud \ud Conclusions \ud \ud Band 3 CEINGE alters function from that of anion exchange to cation transport, affects the membrane tyrosine phosphorylation profile, in particular of band 3 and stomatin, and its presence during red cell development likely contributes to dyserythropiesis

A new molecular link between defective autophagy and erythroid abnormalities in chorea-acanthocytosis

“…22,23,25,28,30 Syk-phosphorylated membranes were used as substrates, as described in De Franceschi et al 14 …”

“…14,[19][20][21] Red cell membrane (ghost) and cytosol fractions were obtained as previously reported. [22][23][24] Immunoblot 23, 25 and immunoprecipitation (IP) 14,[26][27][28] were carried out as previously reported (see supplemental Materials and methods for details). When required, the IP assays were carried out as required in the absence or presence of the GST-Lyn/SH3 domain or of the inhibitors PP2 or geldanamycin (GA).…”

The hereditary stomatocytoses

“…4 The known HSt point mutations in band 3 are illustrated in Figure 2, and occur in a restricted region of the transmembrane domain of the protein. In the current issue of the journal, Iolascon et al 7 report a new mutation in band 3, associated with hereditary stomatocytosis (Gly796Arg). The proband also displays dyserythropoiesis that is phenotypically similar to congenital diserythropoietic anemia (CDA) type 1.…”

Structural Model of the Anion Exchanger 1 (SLC4A1) and Identification of Transmembrane Segments Forming the Transport Site

“…A few years ago, some specific point mutations were characterized and proposed to convert the electroneutral anion exchanger into a cation-conductive pathway (5,6). These mutations are associated with human pathologies (hereditary hemolytic anemia and distal renal tubular acidosis) (7)(8)(9)(10). In addition to naturally occurring mutations identified in patients with hereditary stomatocytosis or distal renal tubular acidosis, a sequence-function analysis of AE1 revealed other amino acids crucial for transport properties of the protein (11).…”

“…It was already known that either AE1 could be converted into a cation conductance or that a cation conductance could be observed in a still functional anion exchanger. These peculiar transport features result from specific point mutations in the transmembrane domain (such as H734R in TM10), and some of these point mutations are associated with hereditary red cell or renal diseases (5,(7)(8)(9)(10)46). Our present results extend to TM5 the list of amino acids that, when substituted in AE1, induce a Na ϩ and K ϩ leak in Xenopus oocytes.…”