Detection of membrane associated thioredoxin on human cell lines

Thioredoxin (TRX) is a ubiquitous dithiol-oxidoreduction enzyme broadly expressed in cells from prokaryote to eukaryote organisms. Human thioredoxin (human TRX) gene, previously cloned in our laboratory, codes for a 12-kDa protein found in the culture supernatant of several hemopoietic human cell lines. This protein is secreted by a nonclassical pathway. The role of the secreted enzyme as a signalling soluble mediator was demonstrated, but nothing is known about a membrane associated form of thioredoxin which could be involved in cell/cell contacts and accessory signal function. Thus, we performed experiments to determine if human TRX is also expressed at the cell surface. We report here positive results based upon indirect immunofluorescence flow cytometric analysis of different human cell lines (HeLa, U 937, Jurkat, 3B6, Daudi and Raji) using a cross reactive sheep anti E. coli TRX polyclonal antibody demonstrating a significant expression of human TRX at the surface of human cells.