Functional characterization of pactolus, a beta-integrin-like protein preferentially expressed by neutrophils

Murine Pactolus is a beta -integrin-like molecule expressed exclusively on the surface of granulocytes. Cell surface expression of Pactolus is dramati cally increased following activation of bone marrow neutrophils with known agonists, and cross-linking of cell surface Pactolus, suggesting the bulk o f the protein is in intracellular stores. The mature protein is found in tw o forms depending upon the extent of N-linked glycosylation. There is no ev idence to suggest that Pactolus requires an associated a chain for expressi on. In some mouse strains, a truncated form of the protein is predicted bas ed upon alternative splicing: this form, however, is unstable and rapidly d egraded after synthesis. Differences in the quantities of these Pactolus mR NA isoforms have defined two alleles. BALB/c and C3H/HeJ mice possess allel e B and preferentially express the truncated, unstable product, whereas C57 BL/6 mice possess allele A and only produce the membrane-bound form. Sequen ce 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 p roduct. The increased expression of the membrane form of Pactolus by granul ocytes of C57BL/6 mice suggests a compensatory adhesion function that is re duced in cells from the low producing strains.