Engineering CHO cells to overexpress a secreted reporter protein upon induction from mouse mammary tumor virus promoter.
The mouse mammary tumor virus (MMTV) promoter is induced by the addition of a glucocorticoid hormone or analog such as dexamethasone. The hormone binds to its specific transcription factor, glucocorticoid receptor (GR), and the activated complex then binds to the glucocorticoid response elements (GREs) in the enhancer region of the MMTV promoter to induce the overexpression of downstream genes. We have constructed an expression vector for a reporter protein, secreted alkaline phosphatase (SEAP),controlled by the MMTV promoter and co-transfected this vector along with a GR expression cassette into Chinese hamster ovary (CHO) cells. High producers were cloned and grown in suspension cultures. A very high titer, over 0.4 mg/mL, of SEAP was obtained from this inducible overexpression system, about ten times that achievable with the same reporter protein using the strong constitutive SV40 promoter in CHO cells. A peak production rate of 187 pg SEAP per cell per day was observed within 3 days after induction, compared to the peak rate of 23 pg SEAP per cell per day expressed using the constitutive SV40 promoter. With the reduced or zero growth rate during the protein production phase, this novel MMTV overexpression system is highly suited for optimizing glycoprotein synthesis rates in high cell density fed-batch or perfusion bioreactors.
James
R I
RI
Department of Chemical Engineering, University of Colorado, Boulder, Colorado 80309-0424, USA.
Elton
J P
JP
Todd
P
P
Kompala
D S
DS
D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D016466:CHO Cells / Q000502:physiology*; D006224:Cricetinae; D003470:Culture Media; D017930:Genes, Reporter; D005818:Genetic Engineering / Q000379:methods*; D005822:Genetic Vectors; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics*; D011401:Promoter Regions, Genetic; D015202:Protein Engineering / Q000379:methods; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics* / Q000378:metabolism*; D013539:Simian virus 40 / Q000235:genetics; D014162:Transfection
D003470:Culture Media; D011965:Receptors, Glucocorticoid; D011994:Recombinant Proteins; D000469:Alkaline Phosphatase