Stromal cells selectively reduce the growth advantage of human committed CD34+ hematopoietic cells ectopically expressing HOXB4.
Key players in self-renewal of hemopoietic stem cells are homeobox (HOX) transcription factors. In murine cells, overexpression of HOXB4 results in expansion of hematopoietic stem- and committed progenitor cells in vitro without obvious hematopoietic alterations. In vivo, HOXB4 induced HSC expansion continued until stem cell regeneration reached pretransplantation levels. HOXB4 is thus an attractive candidate for amplification of stem cells provided that human HOXB4 overexpressing cells can also be restricted to normal growth in vivo. The stromal microenvironment provides the regulatory mechanisms controlling the balance of stem cell self-renewal and differentiation. Here, we compared the response of HOXB4- and GFP-control vector transduced human CD34(+) cells to stroma encoded signals in vitro. In serum-sustained cocultures MS-5 stroma contact reduced the output of late CD34- HOXB4(+) cells in relation to GFP-controls 9-fold whereas the expansion of early CD34(+)HOXB4(+) cells remained unchanged as compared to liquid cultures. In presence of insulin HOXB4 overexpressing cells do not react to stroma encoded growth-restricting signals. Our results show that ectopic expression of HOXB4 in combination with MS-5 stroma exerts different effects in early and late human cord blood CD34(+) cells resulting in an enhanced proliferation of early CD34(+) cells in absence or presence of MS-5 stroma and an impaired output of late committed CD34(+) cells on MS-5 stroma.
Friel
Jutta
J
University Hospital Eppendorf, Department of Oncology and Hematology, Transplantation Unit, Hamburg, Germany.
Schiedlmeier
Bernhard
B
Geldmacher
Maren
M
Ostertag
Wolfram
W
D000818:Animals; D018952:Antigens, CD34 / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D005312:Fetal Blood / Q000166:cytology; D015870:Gene Expression; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000502:physiology; D051379:Mice; D044967:Serum / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*
D018952:Antigens, CD34; C090460:HOXB4 protein, human; D018398:Homeodomain Proteins; C513262:Hoxb4 protein, mouse; D007328:Insulin; D014157:Transcription Factors