Regulator of differentiation 1 (ROD1) binds to the amphipathic C-terminal peptide of thrombospondin-4 and is involved in its mitogenic activity

✍ Scribed by Gulzhakhan Sadvakassova; Monica C. Dobocan; Marcos R. Difalco; Luis F. Congote

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 224 KB
• Volume: 220
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.21817

✦ Synopsis

Abstract

The matrix protein thrombospondin‐4 has an acidic amphipathic C‐terminal peptide (C21) which stimulates erythroid cell proliferation. Here we show that C21 stimulates red cell formation in anemic mice in vivo. In vitro experiments indicated that the peptide‐mediated increase of erythroid colony formation in cultures of human CD34+ hematopoietic progenitor cells was possible only under continuous presence of erythropoietin. In the absence of this cytokine, C21 stimulated exclusively myeloid colony formation. Therefore, the peptide is not a specific erythroid differentiation factor. In fact, it is mitogenic in non‐erythroid cells, such as skin fibroblasts and kidney epithelial cells. In erythroleukemic TF‐1 cells, it actually decreased the production of the erythroid differentiation marker glycophorin A. C21‐affinity chromatography revealed regulator of differentiation 1 (ROD1) as a major C21‐binding protein. ROD1 is the hematopoietic cell paralog of polypyrimidine tract binding proteins (PTBs), RNA splice regulators which regulate differentiation by repressing tissue‐specific exons. ROD1 binding to C21 was strongly inhibited by synthetic RNAs in the order poly A > poly U > poly G = poly C and was weakly inhibited by a synthetic phosphorylated peptide mimicking the C‐terminal domain of RNA polymerase II. Cellular overexpression or knockdown experiments of ROD1 suggest a role for this protein in the mitogenic activity of C21. Since the nuclear proteins ROD1 and PTBs regulate differentiation at a posttranscriptional level and there is a fast nuclear uptake of C21, we put forward the idea that the peptide is internalized, goes to the nucleus and maintains cells in a proliferative state by supporting ROD1‐mediated inhibition of differentiation. J. Cell. Physiol. 220: 672–679, 2009. © 2009 Wiley‐Liss, Inc.