Tandem Repeat Polymers of a Critical Region of the Human Interferon-β Promoter Exhibit a Marked Constitutive Activity and Enhanced Responsiveness to Transcriptional Regulators in Transfected HeLa Cells

Multiple copy tandem repeats polymers of an authentic 30-bp region of the human interferon-β (IFN-β) promoter between positions −91 to −62 relative to the cap site or the hexanucleotide GAAAGT derived from this region, both acted as strong constitutive regulatory elements in transfected HeLa cells. Such polymers were unresponsive to treatment with IFN-α despite their considerable homology with the IFN-responsive elements of other genes but were highly responsive to treatment of HeLa cells with IFN-γ. Virus induction of HeLa cells transfected with polymers of the 30-bp region linked to a CAT gene increased the activity of the reporter gene 500- to 2,000-fold over baseline levels. Treatment with IFN-α prior to virus induction did not increase further CAT activity. Cotransfection of HeLa cells with the CAT gene under the control of a 12-element tandem repeat polymer of the human IFN-β promoter and an expression vector for the IRF-1 transcriptional activator markedly increased CAT activity while cotransfection of HeLa cells with the IFN-β construct together with an expression vector for the transcriptional regulator IRF-2 markedly decreased CAT activity relative to cells transfected with the IFN-β polymer alone.