Codanin-1, the Protein Encoded by the Gene Mutated in Congenital Dyserythropoietic Anemia Type I ( CDAN1 ), Is Cell Cycle Regulated

Congenital dyserythropoietic anemia (CDA) type I is an inherited autosomal recessive macrocytic anemia associated with ineffective erythropoiesis and the development of secondary hemochromatosis. Distinct erythroid precursors with inter-nuclear chromatin bridges and spongy heterochromatin are pathognomonic for the disease. The mutated gene ( CDAN1 ) encodes a ubiquitously expressed protein of unknown function, codanin-1. Based on the morphological features of CDA type I erythroblasts and the preliminary data on the Drosophila homolog, dlt , which was found to be required for cell survival and cell cycle progression, we investigated the location and the behavior of codanin-1 during the cell cycle. Using immunofluorescence and immune electron microscopy, we localized codanin-1 to the heterochromatin in interphase cells. During the cell cycle, high levels of codanin-1 were observed in S phase. At mitosis, codanin-1 underwent phosphorylation, which coincided with exclusion from condensed chromosomes. The proximal CDAN1 gene promoter region, never before characterized, was found to contain 5 putative E2F1 binding sites. E2F transcription factors are the main regulators of G1/S transition. Cotransfection of an E2F1 expression plasmid increased luciferase activity, confirming that E2F1 activates the transcription of CDAN1, and chromatin immunoprecipitation identified the codanin-1 promoter as a direct target of E2F1. Taken together, these data suggest that codanin-1 is a cell cycle-regulated protein active in S-phase. Based on the localization of codanin-1 to the heterochromatin and the spongy appearance of heterochromatin in CDA I, we suggest that codanin-1 may be involved in heterochromatin organization during DNA replication. This represents the first work towards understanding the function of the proteins involved in CDAs.