Differential expression of Q4 proteins (Qb-1) in fibroblasts and lymphocytes

The Qb-1 protein is coded for by the Q4 gene. This gene appears to be widely transcribed in murine tissues. We have examined the subcellular localization and processing of Qb-1 in fibroblast cells. This protein has previously been reported to be secreted from activated lymphocytes. However, we report that high levels of Qb-1 are present on the surface of B10.P fibroblast cells. We also observed an unusual intracellular distribution for Qb-1. The protein appears to be highly concentrated in the endoplasmic reticulum, in addition to being on the surface. This distribution is not due to inefficient processing. The kinetics of Qb-1 processing and transport are not unusual for class I molecules. Complete resistance to endo-beta-N-acetylglucosaminidase H is acquired, indicating terminal processing. This unusual localization in fibroblast cells and the differential expression of this protein between cell types may reflect a specific role for Qb-1.