Proc Natl Acad Sci USA. situated at focal contact sites. In both neurons and astrocytes examined after shearing, clathrin and -adaptin were colocalized with PP on the surface that directly contacts the substratum. These results are consistent with the putative role of PP in cell adhesion and suggests that PP either interacts Chlormadinone acetate with selected integrins or shares comparable cellular machinery to promote cell adhesion. and results in the secretion of the N-terminal ectodomain PPS. The ubiquitous -secretase cleavage occurs within the A region and therefore precludes the generation of an intact A peptide (Esch, 1990). In contrast to most non-neural cells, neurons and glia secrete relatively small amounts of PPS for unclear reasons (Haass et al., 1991). Some PP molecules not IL12RB2 cleaved around the cell surface are internalized and targeted to endosomes and lysosomes. A smaller populace of PP molecules seems to be recycled back to the surface for secretion or internalization (Koo et al., 1996). Both the secretory and endocytic pathways have been shown to contribute to A released into medium by cultured cells, although endocytic processing seems to be the predominant source (Koo and Squazzo, 1994). The physiological role of PP remains to be defined. Proposed functions for PPS include neurite-promoting properties, wound healing, cell adhesion, cell growth and differentiation, and inhibition of proteases and coagulation factor XIa (for review, seeSaitoh and Mook-Jung, 1996). Full-length membrane-bound PP may function as a cell surface receptor capable of interacting with G-proteins (Nishimoto et al., 1993) and in cell adhesion. The latter function is consistent with the binding of PP with laminin and proteoglycans (Small et al., 1996). Which of these diverse functions predominates in brain is usually unclear. In cultured neurons, cell surface PP is located predominantly in axons, where it subsequently can undergo retrograde and trans-cytotic transport. Surprisingly, around the axonal surface, PP displayed a characteristic patchy pattern. In particular, PP is usually distributed in discontinuous and irregularly spaced segments along the entire length of the axon (Yamazaki et al., 1995). This pattern of PP distribution around the axonal surface is in sharp contrast to the diffuse localization seen intracellularly. We hypothesize, therefore, that this unique PP localization around the axonal surface is related to its putative role of PP in cell adhesion. To investigate further the basis for Chlormadinone acetate this intriguing distribution of PP on the surface of Chlormadinone acetate neurons and to gain insights into the function of surface molecules, we conducted a detailed immunocytochemical analysis of the distribution of PP, integrins, clathrin, and -adaptin in different neural cells. Our results demonstrate that PP is usually colocalized with integrins on the surface of both neurons and astrocytes. In the latter cells, PP accumulates at sites of point contact, but not at focal contact sites. In both cell types, PP shows a tight association with the 11 integrin heterodimer. These observations suggest that PP either interacts directly with selected integrins or, more likely, shares comparable cellular machinery to promote attachment of cells to the substratum. MATERIALS AND METHODS Cultures contacts, whereas 51 integrin is usually associated with contacts, the latter seen in flattened astrocytes after long-term culture (Tawil et al., 1993). Using this culture paradigm, we located cell surface PP at the periphery of the astrocytes shortly after plating, where the staining colocalized tightly with 1 integrin (Fig. ?(Fig.44astrocytes that had been cultured for 3 d appeared in a fine punctate pattern diffusely distributed around the plasma membrane (Fig. ?(Fig.44(Klier et al., 1990). Nonetheless, taken together, we hypothesize that PP at the cell surface functions in an integrin-like manner by interacting with comparable ECM and intracellular cytoskeletal constituents at sites of point contacts to facilitate neuronal adhesion and outgrowth. Although our study did not address the nature of this PP/integrin association, it is tempting to postulate that a direct PP and integrin conversation occurs at the cell surface, possibly via the RHDS sequence, to produce a synergistic effect on cell.
Proc Natl Acad Sci USA