Part I. Bcl-2 and Bcl-x(L) limit apoptosis upon infection with alphavirus vectors

Viral expression systems offer the ability to generate high levels of a par ticular protein within a relatively short period of time. In particular, al phavirus constructs based on Sindbis virus (SV) and Semliki Forest virus (S FV) are promising vehicles as they are cytoplasmic vectors with the potenti al for high expression levels. Two such alphavirus vectors were utilized du ring the current study to infect two commercially relevant cell lines, baby hamster kidney (BHK) and Chinese hamster ovary (CHO); the first was a full y competent SV derivative carrying the gene for chloramphenicol acetyltrans ferase (dsSV-CAT), while the second was a replication deficient SFV constru ct containing the human interleukin-12 (IL-12) p35 and p40 genes (SFV-IL-12 ). Since infection with these vectors induced apoptosis in both cell lines, the present effort was dedicated to determining the ability of anti-apopto sis genes to limit the cell death associated with these virus constructs. I nfection with the dsSV-CAT vector resulted in the rapid death of BHK and CH O cells within 4 days, a phenomenon which was considerably delayed by stabl y overexpressing bcl-2 or bcl-X-L. In fact, cellular lifespans were doubled in both BHK-bcl2 and CHO-bclx(L) cells relative to the parental cell lines . Furthermore, the presence of these gene products provided increases of up to 2-fold in recombinant CAT production. Overexpression of bcl-2 and bcl-x (L) also altered the response of these cells upon infection with SFV-IL-12. While the parental cell lines were completely nonviable within 1 week, the BHK-bcl2, BHK-bclx(L), and CHO-bclx(L) cells each recovered from the infec tion, resuming exponential growth and regaining viabilities of over 90% by 9 days post-infection. Total IL-12 productivities were nearly doubled by Bc l-2 and Bcl-x(L) in the CHO cells, although this effect was apparently cell -line specific, as the native BHK cells were able to secrete more IL-12 tha n either of its transfected derivatives. Regardless, the presence of the an ti-apoptosis genes allowed the production of IL-12 to be maintained, albeit at low levels, from each of the cell lines for the duration of the culture process. Therefore, overexpression of bcl-2 family members can have a sign ificant impact on culture viabilities and recombinant protein production du ring alphavirus infections of mammalian cells. (C) 2000 John Wiley & Sons, Inc.