Inhibition of erythropoiesis by Smad6 in human cord blood hematopoietic stem cells.
Bone morphogenetic proteins (BMPs) that belong to the transforming growth factor-β (TGF-β) superfamily cytokines, play crucial roles in hematopoiesis. However, roles of Smad6 in hematopoiesis remained unknown in contrast to the other inhibitory Smad (I-Smad), Smad7. Here we show that Smad6 inhibits erythropoiesis in human CD34(+) cord blood hematopoietic stem cells (HSCs). Smad6 was specifically expressed in CD34(+) cord blood HSCs, which was correlated with the expression of BMP2/4/6/7 and BMP type I receptor (BMPRI). BMP-specific receptor-regulated Smads (R-Smads), Smad1 and Smad5 in cooperation with Smad4 induced transcription of the Smad6 gene. Instead of affecting cell cycle, apoptosis, self-renewal, and stemness of CD34(+) cells, Smad6 knockdown enhanced, whereas Smad6 overexpression suppressed erythropoiesis in stem cell culture and colony formation assay. Consistently, Smad6 suppressed the expression of the genes essential for erythropoiesis, such as Kruppel-like factor 1 (erythroid) (KLF1/EKLF) and GATA binding protein 2 (GATA-2). Promoter analyses showed that Smad6 repressed Smad5/4-induced transcription of the Klf1 gene. Thus, our data suggest that Smad6 indirectly maintains stemness by preventing spontaneous erythropoiesis in HSCs.
Laboratory of Immunology, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Republic of Korea.
Young-Ju
YJ
Kang
Ji-woong
JW
Shin
Jeong-Hwan
JH
Yoon
Il-Hwan
IH
Oh
Soon-Pyo
SP
Lee
Suk-Young
SY
Kim
Seok Hee
SH
Park
Mizuko
M
Mamura
D018952:Antigens, CD34 / Q000032:analysis; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics; D055415:Bone Morphogenetic Protein 4 / Q000235:genetics; D055418:Bone Morphogenetic Protein 6 / Q000235:genetics; D055419:Bone Morphogenetic Protein 7 / Q000235:genetics; D052005:Bone Morphogenetic Protein Receptors, Type I / Q000235:genetics; D002478:Cells, Cultured; D004920:Erythropoiesis / Q000235:genetics*; D005312:Fetal Blood / Q000166:cytology; D050989:GATA2 Transcription Factor / Q000235:genetics; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000235:genetics; D011401:Promoter Regions, Genetic; D051905:Smad6 Protein / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D018952:Antigens, CD34; C525718:BMP2 protein, human; C525809:BMP4 protein, human; C525816:BMP6 protein, human; C525819:BMP7 protein, human; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D055418:Bone Morphogenetic Protein 6; D055419:Bone Morphogenetic Protein 7; D050989:GATA2 Transcription Factor; C494711:GATA2 protein, human; D051741:Kruppel-Like Transcription Factors; C497802:SMAD6 protein, human; D051905:Smad6 Protein; C080774:erythroid Kruppel-like factor; D052005:Bone Morphogenetic Protein Receptors, Type I