Expression of tapasin in rainbow trout tissues and cell lines and up regulation in a monocyte/macrophage cell line (RTS11) by a viral mimic and viral infection

• Tapasin protein is a widely expressed 48 kDa protein, but also has a 20 kDa form.
• Tapasin 48 kDa protein is upregulated in 3 days by poly I:C and viral infection.
• Tapasin upregulation is co-ordinated with MH class I upregulation.
• The 20 kDa form of tapasin is not upregulated upon stimulation.

Tapasin is a transmembrane glycoprotein that acts as a bridge between the transporter associated with antigen processing and the MHC class I receptor in mammals. Through the development of antibody against trout tapasin, this report demonstrates the detection of trout tapasin as a N-glycosylated 48 kDa protein. Tissue and cell line distribution revealed that tapasin protein is expressed mainly in immune system organs and in rainbow trout epithelial cell lines from gill (RTgill-W1), liver (RTL-W1), and intestine (RTgutGC). An additional 20 kDa band was observed in tissues and cell lines, and appeared to be most prominent in RTgutGC but was absent in peripheral blood leukocytes. Tapasin 48 kDa protein was most strongly expressed in RTS11 (monocyte/macrophage cell line) and its regulation following dsRNA stimulation was explored. Upon poly I:C treatment and Chum Salmon Reovirus (CSV) infection, tapasin protein expression was upregulated up to 3.5 fold and 3 fold respectively, in parallel with increased expression of the glycosylated MH class I heavy chain, whereas the expression of the 20 kDa form remained unchanged. Overall this work demonstrates the induction of tapasin protein by dsRNA stimulation, which implies its possible conserved regulation during viral infection in teleost cells.