[Structure and Function of an Alternative Splicing Isoform of Stimulator of Interferon Genes STING(sv)]

Stimulator of interferon genes (STING) is an important protein of the innate immune response, and protects against viral infections. To search for an alternative splicing isoform of STING, we undertook rapid amplification of cDNA ends (RACE) and RT-PCR with RNA extracted from human embryonic kidney (HEK) 293 cells and primers designed according to the mRNA sequence of full-length STING(NM-198282. 82). The new sequence was compared using a bioinformatics method. Then, a newly discovered, alternative splicing isoform of STING, named "STING(sv)", and STING(wt) were subcloned into the eukaryotic expression vector pEGFP-C1 and pcDNA 3. 1. Whole-cell extracts were analyzed by western blotting and then probed with monoclonal antibody against enhanced green fluorescent protein (EGFP) after transfection of EGFP-STING(wt) and EGFP-STING(wt) plasmids in HEK293 cells. pcDNA-STING(wt) and pcDNA-STING(wt) were transfected in HEK293 cells, and the luciferase assay carried out. Compared with STING(wt), STING(sv) lacks exon 7 so that shift in the reading frame may produce a protein with a different C-terminal in amino acids 1-30. Western blotting confirmed an expected strong band at 58 x 10(3) kD. The functional luciferase assay showed that STING(sv) inhibited the activity of the interferon (IFN)-β promoter. STING(sv) can be expressed in multiple tissues and distinct cell lines. Our discovery of a new, alternative splicing isoform of STING provides new insights into the functional regulation of STING. STING(sv) could be a dominant negative inhibitor for the activity of the IFN-β promoter in the virus-infection pathway. Hence, STING(sv) could participate in the "fine tuning" of the virus-induced activation of IFN. Therefore, exploring the role of STING(sv) in the pathogenesis of human diseases could be very worthwhile.