Thrombospondin-1 Signaling through CD47 Inhibits Self-renewal by Regulating c-Myc and Other Stem Cell Transcription Factors

Abstract

Signaling through the thrombospondin-1 receptor CD47 broadly limits cell and tissue survival of stress, but the molecular mechanisms are incompletely understood. We now show that loss of CD47 permits sustained proliferation of primary murine endothelial cells, increases asymmetric division, and enables these cells to spontaneously reprogram to form multipotent embryoid body-like clusters. c-Myc, Klf4, Oct4, and Sox2 expression is elevated in CD47-null endothelial cells, in several tissues of CD47- and thrombospondin-1-null mice, and in a human T cell line lacking CD47. CD47 knockdown acutely increases mRNA levels of c-Myc and other stem cell transcription factors in cells and in vivo, whereas CD47 ligation by thrombospondin-1 suppresses c-Myc expression. The inhibitory effects of increasing CD47 levels can be overcome by maintaining c-Myc expression and are absent in cells with dysregulated c-Myc. Thus, CD47 antagonists enable cell self-renewal and reprogramming by overcoming negative regulation of c-Myc and other stem cell transcription factors.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

“…Several of the CD47 redox signaling targets discussed here coincide with genes that exhibit significantly altered expression in a global transcriptome analysis of WT versus Cd47 -/-mouse lung endothelial cells, including Nos, Txnip, and NADPH oxidase genes (113). However, examination of the resulting regulatory network reveals a larger number of CD47-dependent genes for which we currently have no understanding of how TSP1 and CD47 regulate their expression (Fig.…”

“…TSP1 signaling through CD47 has also emerged as an inhibitor of stem and nonstem cell self-renewal and the genes that coordinate this process (112,113,217), which has implications for age-related loss in healing capacity and for tissue regeneration using stem cell therapy and in tissue bioengineering. It will be necessary to fully define how CD47 functions to balance and, when activated by ligands such as TSP1, imbalance these multiple pathways.…”

“…-/-mouse lung endothelial cells (113). Extracted data for genes on this list were subjected to Ingenuity pathway analysis.…”

“…Cd47 -/-cells could be passaged continuously upward of 6 months with no loss of proliferative capacity. In contrast, lung endothelial cells from WT mice could not be passaged more than three or four times before becoming senescent as assessed by induction of senescence-associated b-galactosidase activity (113). Null cells continued to display normal endothelial cell morphology even after extended passage.…”

“…Re-expression of CD47 in the CD47-deficient Jurkat cells suppressed cMyc expression. Conversely, in lossof-function experiments, suppression of CD47 with a morpholino oligonucleotide in isolated endothelial cells and in mice increased mRNA expression of several self-renewal transcription factors (113).…”