Isoprenaline-induced and constitutive members of a proline-rich protein sub-group from mouse parotid glands studied with monoclonal antibody NAL1.

Members of the proline-rich protein (PRP) family of mouse parotid glands were analysed before and after stimulation with the beta-agonist isoprenaline by using a monoclonal antibody raised against the induced PRP A3(0) (GP-27). Antibody NAL1 reacted strongly with isoprenaline-induced B-type PRP precursors and their salivary counterparts, but not against the A-type PRPs A1(0) (Gp-66) and A2(0) (GP-45) or human salivary proteins, and it is likely that NAL1 recognizes a proline-rich repeat variant unique to this group of rodent PRPs. PRP-related antigens were observed in the parotid glands (N1(0) and N2(0] and saliva of normal mice. The antigens were located immunocytochemically in secretory granules of parotid acinar cells of both normal and isoprenaline-stimulated mice. The total amount of PRP antigens increased 16-fold from 2.5 to 40% of parotid protein after 10 days of isoprenaline treatment, as estimated by enzyme-linked immunosorbent assay. Immunoblotting showed that new PRP species appeared during the period of increase. After treatment with isoprenaline, B-type PRPs appeared first, followed by A3(0) and another member of the family. These results show that the mouse PRP family is larger than previously thought and can be divided immunologically into sub-groups. That a subset of PRPs are produced in the normal mouse indicates that there is differential beta-adrenergic regulation within the family, and also has implications for the role of PRPs in the normal maintenance of healthy dentition and other processes.