Novel Model of Stimulation-Responsive Splicing for Generation of Immunogenic Isoforms of Tumor Antigens and Autoantigens.

Alternative splicing is a process that removes introns and alters exons to generate multiple isoforms from a single pre-mRNA transcript. Alternative splicing is the major mechanism by which a small number of human genes (6 × 10⁴) can encode the larger complexity of the human proteome (1 × 10⁶ proteins). Previously we demonstrated that alternative splicing of apoptosis-regulatory protein transcripts regulates immune responses by modulating lymphocyte survival (Immunity, 1997; Mol. Immunol. 2002; J Exp Med, 2002; Oncogene 2005; Biochem J, 2005). To examine the hypothesis that alternative splicing plays a role in selection of nonmutated self-protein isoforms for tumor antigens and autoantigens, recently, we showed that alternative splicing is a major mechanism in regulation of the immunogenicity of tumor antigen CML66 (J. Immunol. 2004). In addition, we found that alternative splicing occurs in 100% of the autoantigen transcripts. This is significantly higher than the approximately 42% rate of alternative splicing observed in the 10,000 randomly selected human gene transcripts (p<0.001) [J. Allergy Clin. Immunol., 2004 (cover article)]. Here, we report that essential alternative splicing factor ASF/SF2 expression in samples from patients with chronic inflammation is lower than that of the healthy controls (p<0.05). In addition, TNF-a significantly downregulates ASF/SF2 expression (7 folds) in cultured cells in comparison to the expression variations of b-actin control. These findings demonstrate that ASF/SF2, presumably affecting splicing of self-antigen transcripts, is downregulated in autoimmune inflammatory disease potentially via a TNF-a-mediated pathway. Collectively, we propose for the first time a novel model of “stimulation-responsive splicing”, which emphasizes that stimulation-responsive splicing plays a critical role in selection of nonmutated self-protein isoforms to become tumor antigens and autoantigens (Clin. Immunol. Invited Review, in press, 2006). The new model for the definition of immunogenic isoforms of tumor antigens and autoantigens is significant in facilitating the development of:

1. immunogenic antigen isoform microarrays for disease diagnosis and prognosis;

2. autoantigen-tolerizing therapy and splicing-redirection therapy for autoimmune diseases; and

3. immunogenic antigen isoforms-based immunotherapy for tumors.