Induction of gene expression by intracellular interferon-gamma: abrogation of the species specificity barrier.
We reported previously that murine L-929 cells expressing a human interferon (IFN)-gamma cDNA lacking a signal peptide sequence synthesize but fail to secrete human IFN-gamma and support viral replication at a reduced level. These cells also had elevated levels of IFN-inducible gene products. We show here that a similar response is seen in human cells expressing a mutated murine IFN-gamma cDNA. The ability of human IFN-gamma to induce gene expression in murine cells is shown to be due to the intracellular IFN-gamma rather than to clonal variation, induction of endogenous murine IFN, or alternative mediators of antiviral activity. We have used a murine cell line, Ltk-aprt-, which is resistant to both type I and II IFNs but responsive to combined treatment with both. Ltk-aprt- cells transfected with human IFN-gamma cDNA lacking a signal sequence support virus replication at the same level as control cells. However, unlike transfectants containing only the neoR selection gene, clones expressing the mutated human IFN-gamma gene show strong protection against viral infection and elevated levels of 2,5 A synthetase mRNA and MHC class I protein after treatment with IFN-beta alone. Reverse transcriptase-PCR rules out the induction of endogenous murine IFN expression as a mediator of these effects. Thus, expression of intracellular human IFN-gamma mimics treatment with extracellular murine IFN-gamma in permitting a synergistic response to IFN-beta. Given the inability of human IFN-gamma to bind to the murine cell-surface receptor our results show that intracellular IFN-gamma can activate certain responses independent of cell-surface binding.
Lewis
J A
JA
Department of Anatomy & Cell Biology, SUNY Health Science Center at Brooklyn 11203, USA.
Huq
A
A
Liu
W
W
Jacob
A
A
D000818:Animals; D001483:Base Sequence; D003593:Cytoplasm / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006183:H-2 Antigens / Q000235:genetics; D006801:Humans; D016899:Interferon-beta / Q000096:biosynthesis / Q000494:pharmacology; D007371:Interferon-gamma / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D007739:L Cells / Q000378:metabolism / Q000821:virology; D008574:Mengovirus / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D011118:Polynucleotide Ligases / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D017384:Sequence Deletion; D013045:Species Specificity; D014721:Vesicular stomatitis Indiana virus / Q000502:physiology; D014779:Virus Replication / Q000187:drug effects / Q000502:physiology
D006183:H-2 Antigens; C024755:H-2K(K) antigen; D021382:Protein Sorting Signals; D012333:RNA, Messenger; D016899:Interferon-beta; D007371:Interferon-gamma; C021906:(2'-5')oligo-isoadenylate synthetase; D011118:Polynucleotide Ligases