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

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• 作者：Xiaoyu Tang ; Zengsui Tian ; Pin-Ju Chueh ; Ssuhen Chen ; Dorothy M. Morré ; D. James Morré
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：October 30, 2007
• 年：2007
• 卷：46
• 期：43
• 页码：12337 - 12346
• 全文大小：582K
• 年卷期：v.46,no.43(October 30, 2007)
• ISSN：1520-4995

文摘

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 atthe surface of cancer cells and in sera of cancer patients, is absent from the surface of noncancer cells andfrom sera of healthy individuals. Full-length tNOX mRNA is present in both normal and tumor cells butappears not to be expressed in either. Our research suggests alternative splicing as the basis for the cancerspecificity of tNOX expression at the cell surface. Four splice variants were found. Of these, the exon 4minus and exon 5 minus forms present in cancer cell lines were absent in noncancer cell lines. In contrastto full-length tNOX cDNA, transfection of COS cells with tNOX exon 4 minus cDNA resulted inoverexpression of mature 34 kDa tNOX protein at the plasma membrane. The exon 4 minus form resultedin 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 cellsurface expression of 34 kDa mature tNOX was observed. The unprocessed molecular mass of 47 kDa ofthe exon 4 minus cDNA translated from methionine 231 corresponded to that of the principal nativetNOX form of the endoplasmic reticulum. Taken together, the molecular basis of cancer-cell-specificexpression of 34 kDa tNOX appears to reside in the cancer-specific expression of exon 4 minus splicevariant mRNA.