PECAM‐1 shedding during apoptosis generates a membrane‐anchored truncated molecule with unique signaling characteristics

ABSTRACT Shedding of cell surface molecules, including growth factor receptors, provides a mechanism by which cells regulate signal transduction events. Here we show that platelet‐endothelial cell adhesion molecule (PECAM)‐1 is shed from the endothelial cell surface during apoptosis and accumulates in the culture medium as a ~100 kDa soluble protein. The cleavage mediating the shedding is matrix metalloproteinase (MMP) dependent, as GM6001, a broad‐spectrum MMP inhibitor, inhibits PECAM‐1 accumulation in the culture medium in a dose‐responsive manner. In addition to the 100 kDa soluble fragment, PECAM‐1 cleavage generates the formation of a truncated (Tr.) ~28 kDa molecule, composed of the transmembrane and the cytoplasmic PECAM‐1 domains. Transfections of the full‐length (Fl) and the Tr. PECAM‐1 gene constructs into endothelial and nonendothelial cells were performed. We found 1) significantly more γ‐catenin and SHP‐2 bound to the truncated than to the full‐length PECAM‐1;2) stable expression of the truncated PECAM‐1 in SW480 colon carcinoma cells resulted in a dramatic decrease in cell proliferation, whereas expression of comparable levels of the full‐length PECAM‐1 had no effect;3) the decrease observed in cell proliferation is due, in part, to an increase in programmed cell death (apoptosis) and correlated with continuous caspase 8 cleavage and p38/JNKphosphorylation. These results support the intimate involvement of PECAM‐1 in signal transduction cascades and also suggest that caspase substrates (e.g., PECAM‐1) may possess distinct and unique functions on cleavage.—Ilan, N., Mohsenin, A., Cheung, L., Madri, J. A. PECAM‐1 shedding during apoptosis generates a membrane‐anchored truncated molecule with unique signaling characteristics. FASEB J. 15, 362‐372 (2001)