Regulator of differentiation 1 (ROD1) binds to the amphipathic C-terminal peptide of thrombospondin-4 and is involved in its mitogenic activity.
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.
Endocrine Laboratory, McGill University Health Centre, Montreal H3A 1A1, Canada.
Gulzhakhan
G
Sadvakassova
Monica C
MC
Dobocan
Marcos R
MR
Difalco
Luis F
LF
Congote
D021581:Active Transport, Cell Nucleus; D000740:Anemia / Q000097:blood* / Q000139:chemically induced; D000818:Animals; D001665:Binding Sites; D049109:Cell Proliferation; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000378:metabolism; D015672:Erythroid Precursor Cells / Q000378:metabolism*; D004920:Erythropoiesis; D004921:Erythropoietin / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006021:Glycophorins / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000378:metabolism; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D019699:Thrombospondins / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors; D014161:Transduction, Genetic; D015215:Zidovudine
D006021:Glycophorins; C118823:PTBP3 protein, human; D010446:Peptide Fragments; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D019699:Thrombospondins; C101864:thrombospondin 4; D004921:Erythropoietin; D038941:Polypyrimidine Tract-Binding Protein; D015215:Zidovudine