Differential IFN-γ Stimulation of HLA-A Gene Expression through CRM-1-Dependent Nuclear RNA Export

Abstract

IFNs regulate most MHC class I genes by stimulating transcription initiation. As shown previously, IFN-γ controls HLA-A expression primarily at the posttranscriptional level. We have defined two 8-base sequences in a 39-nucleotide region in the 3′-transcribed region of the HLA-A gene that are required for the posttranscriptional response to IFN-γ. Stimulation of HLA-A expression by IFN-γ requires nuclear export of HLA-A mRNA by chromosome maintenance region 1 (CRM-1). Treatment of cells with leptomycin B, a specific inhibitor of CRM-1, completely inhibited IFN-γ induction of HLA-A. Expression of a truncated, dominant-negative form of the nucleoporin NUP214/CAN, ΔCAN, that specifically interacts with CRM-1, also prevented IFN-γ stimulation of HLA-A, providing confirmation of the role of CRM-1. Increased expression of HLA-A induced by IFN-γ also requires protein methylation, as shown by the fact that treatment of SK-N-MC cells or HeLa cells with the PRMT1 inhibitor 5′-methyl-5′-thioadenosine abolished the cellular response to IFN-γ. In contrast with HLA-A, IFN-γ-induced expression of the HLA class Ib gene, HLA-E, was not affected by either 5′-methyl-5′-thioadenosine or leptomycin B. These results provide proof of principle that it is possible to differentially modulate the IFN-γ-induced expression of the HLA-E and HLA-A genes, whose products often mediate opposing effects on cellular immunity to tumor cells, pathogens, and autoantigens.

Posttranscriptional Regulation of HLA-A Protein Expression by Alternative Polyadenylation Signals Involving the RNA-Binding Protein Syncrip

“…3’UTRs encode docking sites for miRNAs (10, 11) as well as RBPs(8, 9), which are the major determinants of post-transcriptional gene regulation. Several reports indicate a role of 3’UTR associated RBPs in the post-transcriptional regulation of HLA genes (14–17), including another member of the heterogeneous nuclear ribonucleoprotein family, HNRNP-R (17). We identified the RBP Syncrip as the translational inhibitor of the long form of the HLA-A 3’UTR.…”

Human DEAD-box protein 3 has multiple functions in gene regulation and cell cycle control and is a prime target for viral manipulation

“…If DDX3 was needed for the export of snRNA via CRM1 it could indirectly have an effect on splicing by affecting the maturation of snRNAs, which are exported from and re-imported into the nucleus before they assemble with other splicing factors into a functional spliceosome [22]. Also, a small subset of inducible mRNAs, including IFN mRNA and IFN -induced HLA-A mRNA [23,24] is exported by CRM1 rather than TAP. Given its recently identified role in anti-viral gene expression [9] (further discussed in sections 3.5 and 5.1), it is tempting to speculate that DDX3 might have a role in mediating the export of these and other immuno-relevant mRNAs.…”

Protein arginine methyltransferase 1 (PRMT1) represses MHC II transcription in macrophages by methylating CIITA

“…FLAG-tagged CIITA, GFP-tagged PRMT1, HA-tagged PRMT1 (WT and EQ), PRMT1 short hairpin RNA (shRNA) plasmid, DRA300 reporter have been previously described67141516. Small interfering RNA (siRNA) for mouse and human PRMT1 was purchased from Dharmacon.…”

“…For instance, Browne et al . have shown that PRMT1 inhibition attenuates the expression of HLA-A, but curiously not HLA-E, by IFN-γ in cancer cells15. PRMT1 has also been shown to repress NF-κB-mediated inflammation by methylating and preventing RelA from binding to target genes16.…”