Im. Wang et al., REGULATION OF TL ANTIGEN EXPRESSION - ANALYSIS OF THE T18(D) PROMOTERREGION AND RESPONSES TO IFN-GAMMA, The Journal of immunology, 151(5), 1993, pp. 2646-2657
Type I (alpha/beta) and type II (gamma) IFN enhance MHC class I gene e
xpression through an IFN-responsive element (IRE) present in the 5' fl
anking region of the class I-a genes. Comparison of the 5' sequences b
etween classical class I-a genes and T region class I-b genes reveals
little homology except for presence of a potential IRE. We have found
that cell surface expression of thymus leukemia Ag (TL) was up-regulat
ed by IFN-gamma to a greater extent than H-2K,D in all TL+ T cell line
s tested. In contrast, IFN-alpha/beta, which significantly increased H
-2K and H-2D Ag expression, had only minor effects on TL expression. R
esting peripheral T cells, which were considered to be TL- from previo
us studies, were found to express TL at a low level as determined by f
low cytometry, immunoprecipitation, as well as polymerase chain reacti
on; the level of expression also could be elevated by IFN-gamma. To ex
amine the control of TL gene transcription and its regulation by IFN-g
amma, varying lengths of the T18d 5' flanking region were analyzed in
chloramphenicol acetyl transferase assays. By deletion analysis, promo
ter activity and IFN-gamma responsiveness were localized to an 86-bp f
ragment that contains the IRE. Both responses were localized further t
o a 32-bp fragment that contained the IRE at its 3' end. RNase protect
ion assays revealed two major transcription initiation sites, one imme
diately 5' of the IRE and another approximately 60 bp downstream. Furt
hermore, polymerase chain reaction analysis of mRNA from resting T cel
ls, thymocytes, and T cell tumor lines confirmed the RNase protection
data. Thus, transcription of T18d initiates much further upstream than
the classical class I genes, can utilize an unusual promoter element,
and can be elevated by IFN-gamma.