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 approximately 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.) approximately 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 gamma-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/JNK phosphorylation. 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.

CD44 Regulation of Endothelial Cell Proliferation and Apoptosis via Modulation of CD31 and VE-cadherin Expression

“…(i) Active caspase-8 expression was suppressed in CD44KO cells as well as active caspase-3, and both were rescued by the expression of mouse CD44 and CD31 in CD44KO cells. These results confirmed that CD31 expression and active caspase-8 are related to each other, as we suggested in 2001 (23). Thus, the attenuated activation of caspase-8 in the absence of CD44 is related to CD31 expression.…”

“…These findings support the concept that CD44 mediates several of its effects in endothelia through modulation of cell junctional molecule expression (e.g. CD31 and VE-cadherin), which, in addition to its known modulation of junctional integrity, matrix metalloproteinase levels and activation, interactions with cortical membrane proteins, and selected signaling pathways, modulates proliferation and apoptosis (22)(23)(24)(25)(26)(27)(28)(29), further defining the integrated roles of CD44, VE-cadherin, and CD31 as critical regulators of vascular function.…”

“…In this report, we demonstrate persistent increased proliferation and reduced activations of both effector and initiator caspases in high cell density, post-confluent CD44 knock-out (CD44KO), 2 and CD31KO cultures and that reconstitution with murine CD44 or CD31 restored the proliferative and caspase activation rates to WT levels under high cell density conditions. In addition, we have confirmed that the CD31 ectodomain plays a key role in specific caspase cascades (23) as well as cell adhesion-mediated cell growth and found that CD31 deficiency results in a reduction in VE-cadherin expression. We also show that both CD44KO and CD31KO endothelial cells exhibit a reduced VE-cadherin expression correlating withincreased survivin expression and increased YAP nuclear localization, consistent with inactivation of the Hippo pathway, resulting in increased PCNA expression and caspase inhibition.…”

ADAM10-mediated Release of Complement Membrane Cofactor Protein during Apoptosis of Epithelial Cells

“…The floating cells represent a population of cells that are in the later stages of apoptosis and cannot be rescued from death (35). We found that after ϳ5-fold increase in the caspase activity the shedding of sCD46 was clearly detected in the immunoblots.…”

CD31 signals confer immune privilege to the vascular endothelium

“…Activated inflammatory cells, including the endothelium, undergo active shedding of the extracellular domain of the CD31 molecule (34,35); this shedding could contribute to the loss of cell-cell adhesion (34) and to the rise in circulating soluble (s)CD31 during inflammatory diseases (35). Although a potential physiologic role of sCD31 serum levels in vivo remains to be determined, the membrane-anchored truncated protein remains capable of signaling (35); hence, the loss of the CD31 extracellular domain should not affect its ability to interfere with apoptosis.…”