Cloning and Characterization of a Gene Expressed during Terminal Differentiation That Encodes a Novel Inhibitor of Growth

Abstract

We report here the cloning and initial characterization of a novel growth-related gene (EEG-1) that is located on the short arm of chromosome 12. Two spliced transcripts were cloned from human bone marrow and human erythroid progenitor cells: EEG-1L containing a 4350-nucleotide open reading frame encoding a putative protein of 1077 amino acids including a C1q-like globular domain, and an alternatively spliced transcript lacking exon 5 (EEG-1S) encodes a significantly smaller coding region and no C1q-like domain. Quantitative PCR revealed expression of both EEG-1 transcripts in all analyzed tissues. Plasmids encoding green fluorescent protein-tagged genes (GFP-EEG-1) were transfected into Chinese hamster ovary cells for localization and functional assays. In contrast to the diffuse cellular localization of the GFP control, GFP-EEG-1L was detected throughout the cytoplasm and excluded from the nucleus, and GFP-EEG-1S co-localized with aggregated mitochondria. Transfection of both isoforms was associated with significantly increased levels of apoptosis. Stable transfection assays additionally demonstrated decreased growth in those cells expressing EEG-1 at higher levels. Quantitative PCR analyses of mRNA obtained from differentiating erythroid cells from blood donors were performed to determine the transcriptional pattern of EEG-1 during erythropoiesis. EEG-1 expression was highly regulated with increased expression at the stage of differentiation associated with the onset of global nuclear condensation and reduced cell proliferation. We propose that the regulated expression of EEG-1 is involved in the orchestrated regulation of growth that occurs as erythroblasts shift from a highly proliferative state toward their terminal phase of differentiation.

Altered ubiquitin causes perturbed calcium homeostasis, hyperactivation of calpain, dysregulated differentiation, and cataract

“…Deficiency of Tdrd7 gene causes juvenile cataract (18). Caprin2 is involved in erythroblast terminal differentiation, processes with extensive similarities to lens cell development (19). Interestingly, Caprin2 is expressed at higher levels upon lens development (20) and is predicted to be a cataract-associated gene (21).…”

Selective Gene Expression in Magnocellular Neurons in Rat Supraoptic Nucleus

“…The highest expression ratio in this group of genes is 24.6 for the C1q domain containing 1 gene. C1q domain containing 1 (also known as EEG-1) has been identified as a novel growth-related gene involved in hematopoetic differentiation and is also believed to also play a general role in terminal differentiation (Aerbajinai et al, 2004). This gene is of particular interest not only because it has an exceptionally high expression ratio, but also because its expression during chronic hyperosmolar conditions increases to 926% of control levels (Fig.…”

Bacterial expression and preliminary crystallographic studies of a 149-residue fragment of human Caprin-1

“…It is possible that the Caprin-1-G3BP1 complex regulates the transport and translation of mRNAs encoding proteins involved in cellular proliferation. In contrast to Caprin-1, the Caprin-2 level is increased at the stage of differentiation (Aerbajinai et al, 2004), suggesting its involvement in the developmental transition from rapid proliferation towards terminal differentiation.…”