Blood, Vol. 95 No. 5 (March 1), 2000:
pp. 1834-1841
Elliptocytosis in patients with C-terminal domain
mutations of protein 4.1 correlates with encoded messenger RNA levels
rather than with alterations in primary protein structure
Madeleine Morinière,
Leticia Ribeiro,
Nicole Dalla Venezia,
Mireille Deguillien,
Philippe Maillet,
Thérèse Cynober,
François Delhommeau,
Helena Almeida,
Gabriel Tamagnini,
Jean Delaunay, and
Faouzi Baklouti
From CNRS URA 1171, Lyon, France; CNRS UMR 5534, Centre de
Génétique Moléculaire et Cellulaire, Université
Lyon 1, Villeurbanne, France; Unidade de Hematologia Molecular,
Serviço de Hematologia, Hospital Pediàtrico de Coimbra,
Coimbra, Portugal; and Service d'Hématologie, d'Immunologie et
de Cytogénétique, and Laboratoire de Biologie
Spécialisée, Hôpital de Bicêtre, INSERM U 473, Le Kremlin-Bicêtre, France.
Early biochemical studies defined 4 functional domains of the
erythroid protein 4.1 (4.1R). From amino-terminal to carboxy-terminal, these are 30 kd, 16 kd, 10 kd, and 22/24 kd in size. Although the
functional properties of both the 30-kd and the 10-kd domain have been
demonstrated in red cells, no functional activities have been assigned
to either the 16-kd or the 22/24-kd domain in these cells. We here
describe new mutations in the sequence encoding the C-terminal
22/24-kd domain that are associated with hereditary elliptocytosis. An
unusually mild phenotype observed in heterozygous and homozygous
members of 1 family suggested heterogeneity in the pattern of
expression of 4.1R deficiency. Using a variety of protein and messenger
RNA (mRNA) quantification strategies, we showed that, regardless of the
alteration in the C-terminal primary sequence, when the protein is
produced, it assembles at the cell membrane. In addition, we found that
alterations in red cell morphologic features and membrane function
correlate with the amount of membrane-associated protein
and therefore
with the amount of mRNA accumulatedrather than with the primary
structure of the variant proteins. These data suggest that an intact
sequence at exons 19 through 21 encoding part of the C-terminal
22/24-kd region is not required for proper protein 4.1R assembly in
mature red cells.
