Erythropoietin enhances the assembly of alpha,beta spectrin heterodimers on the murine erythroblast membranes by increasing beta spectrin synthesis

• Published in: The Journal of biological chemistry Vol. 266; no. 24; pp. 15626 - 15630
• Main Authors: HANSPAL, M, KALRAIYA, R, HANSPAL, J, SAHR, K. E, PALEK, J
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25-08-1991
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Autoradiography; Biological and medical sciences; DNA - genetics; DNA Probes; Erythroblasts - drug effects; Erythroblasts - metabolism; Erythrocyte Membrane - drug effects; Erythrocyte Membrane - metabolism; erythroid cells; erythropoietin; Erythropoietin - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Glycoproteins; Mice; Mice, Inbred BALB C; Proteins; RNA, Messenger - analysis; spectrin; Spectrin - biosynthesis; Spectrin - genetics; Spectrin - metabolism; Transcription, Genetic; Spectrin; Erythropoietin; Rodentia; Activation; Biosynthesis; Glycoproteins; Gene expression; Erythroblast; Dose activity relation; Sialoglycoproteins; Vertebrata; Mammalia; Mouse; Molecular assembly
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)98452-8

Previous biosynthetic studies have revealed that in both mammalian and chicken erythroid cells, alpha spectrin is synthesized
in 2-3-fold excess over beta spectrin. However, in the membrane skeleton, the two polypeptides are assembled in equimolar
amounts, suggesting that the association of alpha spectrin with the membrane skeleton is rate-limited by the amount of beta
spectrin synthesized. Here we have analyzed the synthesis and transcription of alpha and beta spectrin in Friend virus-infected
murine erythroblasts (FVA cells) in vitro during the erythropoietin-dependent period of maturation. Erythropoietin (Epo) increases
the synthesis of beta spectrin but not alpha spectrin, thereby altering the alpha/beta spectrin synthetic ratio. When immature
FVA cells are exposed for 24 h to a standard dose of 0.2 unit/ml Epo for maximum effect, the mRNA content and the synthesis
of beta spectrin are increased resulting in about 1.3-1.5-fold excess of beta spectrin over alpha spectrin in the cytosol.
On the membrane, the incorporation of both alpha and beta spectrins is increased equally by about 30-35%. Furthermore, nuclear
run-off transcription measurements indicate that the increased beta spectrin gene expression is regulated at the level of
transcription. We conclude that in cells with strong Epo stimulus, the expression and synthesis of beta spectrin are increased
resulting in an increase in the amount of alpha,beta spectrin heterodimers available for membrane assembly.