Microsequence analysis of peptides and proteins. IV. Structural studies on human leukocyte interferons

The human interferon alpha species and receptors

Interferon (IFN) was approved by the U.S. Food and Drug Administration on June 5, 1986. As the first biotherapeutic approved, IFN-alpha paved the way for development of many other cytokines and growth factors. Nevertheless, we have just touched the surface of understanding the multitude of human IFNs. This paper reviews the history of the purification of human leukocyte IFN and key aspects of our current state of knowledge of human interferon alpha genes, proteins, and receptors.

Chromatographic methods for purification of leukocyte interferon

A chromatographic method has been developed for obtaining interferon products of three types: with a specific activity of 10(5) I.U./mg of protein (on the basis of leukocyte interferon); with a specific activity of 10(6) I.U./mg of protein (on the basis of leukocyte interferon); a near-homogeneous preparation with an activity of 2 X 10(8)-4 X 10(8) I.U./mg of protein (for leukocyte and recombinant interferons). In the first two cases, only gel permeation chromatography (GPC) is used, which yields interferon preparations containing the oligomeric forms of interferon and also such biologically active proteins as factor D and interleukin-1. In the last case, GPC and immunoaffinity chromatography may be conveniently supplemented by interferon purification by ion exchange to remove immunoglobulins and the products formed by their hydrolytic or proteolytic decomposition.

Differential regulation of interferon synthesis in lymphoblastoid cells

We have examined the molecular mechanisms involved in the induction and regulation of expression of alpha and beta 1 human interferons (HuIFN) in Namalva cells. Cloned IFN-alpha and -beta 1 cDNAs, and antisera to purified IFN-alpha and -beta 1 were used as specific probes to determine the expression of HuIFN genes both on the RNA and protein levels. The rates of gene transcription were correlated with the relative levels of HuIFN mRNA present in induced cells and with the amounts of HuIFN peptides synthesized by these cells. The comparative rate of transcription of HuIFN-alpha and -beta 1 genes was measured in nuclei isolated from Namalva cells before and after induction. No transcription of HuIFN-alpha and -beta 1 genes was detected in nuclei isolated from the uninduced cells. The correspondence in the rate of HuIFN-alpha and -beta 1 genes transcription after virus infection with the relative levels of HuIFN mRNA in the induced cells indicates that the stimulation of HuIFN synthesis by viral infection results from the activation of the transcription of HuIFN genes. The relative levels of alpha and beta 1 induced transcripts were the same in spite of the differences in the number of copies of HuIFN-alpha and -beta 1 genes indicating that the beta 1 gene is transcribed more efficiently than the alpha genes. The steady-state levels of HuIFN-alpha and -beta 1 mRNAs in induced Namalva cells are comparable, however, the overall amount of HuIFN-beta 1 synthesized (as determined by radioimmunoassay and biological activity) is approximately 10-fold lower than that of IFN-alpha. No evidence has been found that would indicate that HuIFN-beta 1 mRNA induced in Namalva cells is different from that induced in human fibroblasts. The data indicate, however, that in Namalva cells, the IFN-beta 1 polypeptide has a higher turnover rate and slower rate of release into medium than the HuIFN-alpha polypeptides, indicating that the observed difference in the overall amounts of these two types of interferons present in the medium is due to regulation on posttranslational level.