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1.  Dual-regulated expression of C/EBP-α and BMP-2 enables differential differentiation of C2C12 cells into adipocytes and osteoblasts 
Nucleic Acids Research  2004;32(1):e1.
CCAAT/enhancer-binding proteins (C/EBPs) as well as bone morphogenic proteins (BMPs) play essential roles in mammalian cell differentiation in shaping adipogenic and osteoblastic lineages in particular. Recent evidence suggested that adipocytes and osteoblasts share a common mesenchymal precursor cell phenotype. Yet, the molecular details underlying the decision of adipocyte versus osteoblast differentiation as well as the involvement of C/EBPs and BMPs remains elusive. We have engineered C2C12 cells for dual-regulated expression of human C/EBP-α and BMP-2 to enable independent transcription control of both differentiation factors using clinically licensed antibiotics of the streptogramin (pristinamycin) and tetracycline (tetracycline) classes. Differential as well as coordinated expression of C/EBP-α and BMP-2 revealed that (i) C/EBP-α may differentiate C2C12 myoblasts into adipocytes as well as osteoblasts, (ii) BMP-2 prevents myotube differentiation, (iii) is incompetent in differentiating C2C12 into osteoblasts and (iv) even decreases C/EBP-α’s osteoblast-specific differentiation potential but (v) cooperates with C/EBP-α on adipocyte differentiation, (vi) osteoblast formation occurs at low C/EBP-α levels while adipocyte-specific differentiation requires maximum C/EBP-α expression and that (vii) BMP-2 may bias the C/EBP-α-mediated adipocyte versus osteoblast differentiation switch towards fat cell formation. Dual-regulated expression technology enabled precise insight into combinatorial effects of two key differentiation factors involved in adipocyte/osteoblast lineage control which could be implemented in rational reprogramming of multipotent cells into desired cell phenotypes tailored for gene therapy and tissue engineering.
PMCID: PMC373304  PMID: 14704358
2.  Identification of a novel proliferation-inducing determinant using lentiviral expression cloning 
Nucleic Acids Research  2003;31(18):e113.
One of the major challenges in the post-genome era is the correlation between genes and function or phenotype. We have pioneered a strategy for screening of cDNA libraries, which is based on sequential combination of lentiviral and oncoretroviral expression systems and can be used to identify proliferation-modulating genes. Screening of a lentiviral expression library derived from adult human brain cDNA resulted in cloning of the potent proliferation-inducing determinant termed pi1 (proliferation inducer 1). Transduction experiments using GFP-expressing oncoretroviruses to target proliferation-competent cells suggested that overexpression of pi1 initiates proliferation of human umbilical vein endothelial cells (HUVECs). Growth induction of HUVECs as well as Swiss3T3 fibroblasts was confirmed by Brd-uridine incorporation assays, which correlated increased DNA synthesis with expression of pi1. The identified pi1 cDNA is 297 bp long and encodes a 10 kDa polypeptide. Since deregulation of proliferation control accounts for a number of today’s untreatable human diseases such as neurodegenerative disorders and cancer, discovery of novel proliferation-modulating genes is essential for developing new strategies for gene therapy and tissue engineering.
PMCID: PMC203339  PMID: 12954789
3.  Streptogramin- and tetracycline-responsive dual regulated expression of p27Kip1 sense and antisense enables positive and negative growth control of Chinese hamster ovary cells 
Nucleic Acids Research  2001;29(4):e19.
We constructed a dual regulated expression vector cassette (pDuoRex) whereby two heterologous genes can be independently regulated via streptogramin- and tetracycline-responsive promoters. Two different constructs containing growth-promoting and growth-inhibiting genes were stably transfected in recombinant Chinese hamster ovary (CHO) cells that express the streptogramin- and tetracycline-dependent transactivators in a dicistronic configuration. An optimally balanced heterologous growth control scenario was achieved by reciprocal expression of the growth-inhibiting human cyclin-dependent kinase inhibitor p27Kip1 in sense (p27Kip1S) and antisense (p27Kip1AS) orientation. Exclusive expression of p27Kip1S resulted in complete G1-phase-specific growth arrest, while expression of only p27Kip1AS showed significantly increased proliferation compared to control cultures (both antibiotics present), presumably by decreasing host cell p27Kip1 expression. In a second system, a derivative of pDuoRex encoding streptogramin-responsive expression of the growth-promoting SV40 small T antigen (sT) and tetracycline-regulated expression of p27Kip1 was stably transfected into CHO cells. Expression of sT alone resulted in an increase in cell proliferation, but the expression of p27Kip1 failed to provide the expected G1-specific growth arrest despite having demonstrated expression of the protein. This illustrates the difficulty in balancing the complex pathways underlying cell proliferation control through the expression of two functionally distinct genes involved in those pathways, and how a single-gene sense/antisense approach using pDuoRex can overcome this barrier to complete metabolic engineering control.
PMCID: PMC29626  PMID: 11160939

Results 1-3 (3)