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The human mRNA encoding the Goodpasture antigen is alternatively spliced
1Fundación Valenciana de Investigaciones Biomédicas, Instituto de Investigaciones Citológicas, Spain.
Abstract:
The noncollagenous (NC1) domain of the human collagen alpha 3(IV)-chain is the primary target of autoantibodies produced in Goodpasture syndrome and, therefore, has been designated as the Goodpasture antigen. In this report, we show that Goodpasture antigen mRNA undergoes processing to at least two alternatively spliced forms in a variety of human tissues, resulting in the exclusion of sequence encoded by either one or two exons. Interestingly, no alternatively spliced forms were observed in bovine or rat tissues. The derived amino acid sequences of the two variant mRNA forms are identical and significantly shorter than that arising from the complete Goodpasture antigen mRNA. They lack the carboxyl-terminal region contributing to the formation of the Goodpasture epitope and all but one of the cysteines found in the complete form. These sequence characteristics suggest that, if translated, the variant Goodpasture antigen is likely to be defective in triple helix formation and no longer reactive with Goodpasture autoantibodies. Although each tissue expressing Goodpasture antigen displayed a specific mRNA pattern, the complete form was always the most abundant and was present at levels apparently unrelated to whether or not the organ of origin is a potential target in Goodpasture syndrome. Furthermore, the antigen sequence was identical in the kidneys of normal and Goodpasture-affected individuals, and no major differences in the expression of the complete and spliced forms were observed.
Insights
Goodpasture antigen mRNA has alternatively spliced forms in human tissues, differing from bovine and rat. These variants may be non-reactive with autoantibodies, impacting Goodpasture syndrome.
Area of Science:
- Molecular Biology
- Immunology
- Genetics
Background:
- The noncollagenous (NC1) domain of human collagen alpha 3(IV)-chain is the Goodpasture antigen, targeted by autoantibodies in Goodpasture syndrome.
- Understanding the molecular variations of this antigen is crucial for comprehending the pathogenesis of Goodpasture syndrome.
Purpose of the Study:
- To investigate the alternative splicing of Goodpasture antigen mRNA in human tissues.
- To characterize the structural and functional implications of these alternatively spliced forms.
Main Methods:
- Analysis of Goodpasture antigen mRNA splicing patterns in various human, bovine, and rat tissues.
- Deduction of amino acid sequences for complete and alternatively spliced forms.
- Comparison of variant sequences with the complete form, focusing on epitope and cysteine residues.
Main Results:
- At least two alternatively spliced forms of Goodpasture antigen mRNA were identified in human tissues, involving the exclusion of one or two exons.
- No alternatively spliced forms were observed in bovine or rat tissues.
- Variant mRNA forms translate to shorter amino acid sequences lacking key regions for epitope formation and triple helix structure, suggesting reduced autoantibody reactivity.
Conclusions:
- Alternative splicing of Goodpasture antigen mRNA occurs in humans, producing variants potentially unable to form the Goodpasture epitope.
- The complete form of the antigen mRNA is most abundant across tissues, irrespective of Goodpasture syndrome relevance.
- No significant sequence or expression differences in antigen forms were found between normal and affected individuals' kidneys.