Alternative Splicing as the Basis for Specific Localization of tNOX, a Unique Hydroquinone (NADH) Oxidase, to the Cancer Cell Surface

作者：Xiaoyu Tang, Zengsui Tian, Pin Ju Chueh, Ssuhen Chen, Dorothy M. Morré, D. James Morré · 发表于：Biochemistry · 年份：2007 · DOI：10.1021/bi700973k · 被引用次数：34 · 研究领域：Coenzyme Q10 studies and effects、Mitochondrial Function and Pathology、Adenosine and Purinergic Signaling

A novel hydroquinone and NADH oxidase with protein disulfide-thiol interchange activity (designated ENOX2 or tNOX), associated exclusively with the outer leaflet of the plasma membrane at the surface of cancer cells and in sera of cancer patients, is absent from the surface of noncancer cells and from sera of healthy individuals. Full-length tNOX mRNA is present in both normal and tumor cells but appears not to be expressed in either. Our research suggests alternative splicing as the basis for the cancer specificity of tNOX expression at the cell surface. Four splice variants were found. Of these, the exon 4 minus and exon 5 minus forms present in cancer cell lines were absent in noncancer cell lines. In contrast to full-length tNOX cDNA, transfection of COS cells with tNOX exon 4 minus cDNA resulted in overexpression of mature 34 kDa tNOX protein at the plasma membrane. The exon 4 minus form resulted in initiation of translation at a downstream M231 initiation site distinct from that of full-length mRNA. With replacement of M231 by site-directed mutagenesis, no translation of exon 4 minus cDNA or cell surface expression of 34 kDa mature tNOX was observed. The unprocessed molecular mass of 47 kDa of the exon 4 minus cDNA translated from methionine 231 corresponded to that of the principal native tNOX form of the endoplasmic reticulum. Taken together, the molecular basis of cancer-cell-specific expression of 34 kDa tNOX appears to reside in the cancer-specific expression of ex...