Functional Characterization of Pactolus, a β-Integrin-like Protein Preferentially Expressed by Neutrophils

Abstract Murine Pactolus is a β-integrin-like molecule expressed exclusively on the surface of granulocytes. Cell surface expression of Pactolus is dramatically increased following activation of bone marrow neutrophils with known agonists, and cross-linking of cell surface Pactolus, suggesting the bulk of the protein is in intracellular stores. The mature protein is found in two forms depending upon the extent of N-linked glycosylation. There is no evidence to suggest that Pactolus requires an associated α chain for expression. In some mouse strains, a truncated form of the protein is predicted based upon alternative splicing: this form, however, is unstable and rapidly degraded after synthesis. Differences in the quantities of these Pactolus mRNA isoforms have defined two alleles. BALB/c and C3H/HeJ mice possess allele B and preferentially express the truncated, unstable product, whereas C57BL/6 mice possess allele A and only produce the membrane-bound form. Sequence analysis has shown the difference between these two alleles is due to a single base pair difference at the splice acceptor site for the truncated product. The increased expression of the membrane form of Pactolus by granulocytes of C57BL/6 mice suggests a compensatory adhesion function that is reduced in cells from the low producing strains.