No abstract

Injury of the tubular epithelium and TGF-beta1-induced conversion of epithelial cells to alpha-smooth muscle actin (SMA)-expressing myofibroblasts are key features of kidney fibrosis. Since injury damages intercellular junctions and promotes fibrosis, we hypothesized that cell contacts are critical regulators of TGF-beta 1-triggered epithelial-to-mesenchymal transition (EMT). Here we show that TGF-beta 1 was unable to induce EMT in intact confluent monolayers, but three different models of injury-induced loss of epithelial integrity (subconfluence, wounding, and contact disassembly by Ca(2+)-removal) restored its EMT-inducing effect. This manifested in loss of E-cadherin, increased fibronectin production and SMA expression. TGF-beta 1 or contact disassembly alone only modestly stimulated the SMA promoter in confluent layers, but together exhibited strong synergy. Since beta-catenin is a component of intact adherens junctions, but when liberated from destabilized contacts may act as a transcriptional co-activator, we investigated its role in TGF-beta 1-provoked EMT. Contact disassembly alone induced degradation of E-cadherin and beta-catenin, but TGF-beta1 selectively rescued beta-catenin and stimulated the beta-catenin-driven reporter TopFLASH. Moreover, chelation of free beta-catenin with the N-cadherin cytoplasmic tail suppressed the TGF-beta1 plus contact disassembly-induced SMA promoter activation and protein expression. These results suggest a beta-catenin-dependent two-hit mechanism in which both an initial epithelial injury and TGF-beta 1 are required for EMT.

Epithelial-mesenchymal-myofibroblast transition (EMT),

Pre-B cell colony-enhancing factor (PBEF) is a highly conserved 52-kDa protein, originally identified as a growth factor for early stage B cells. We show here that PBEF is also upregulated in neutrophils by IL-1β and functions as a novel inhibitor of apoptosis in response to a variety of inflammatory stimuli. Induction of PBEF occurs 5-10 hours after LPS exposure. Prevention of PBEF translation with an antisense oligonucleotide completely abrogates the inhibitory effects of LPS, IL-1, GM-CSF, IL-8, and TNF-α on neutrophil apoptosis. Immunoreactive PBEF is detectable in culture supernatants from LPS-stimulated neutrophils, and a recombinant PBEF fusion protein inhibits neutrophil apoptosis. PBEF is also expressed in neutrophils from critically ill patients with sepsis in whom rates of apoptosis are profoundly delayed. Expression occurs at higher levels than those seen in experimental inflammation, and a PBEF antisense oligonucleotide significantly restores the normal kinetics of apoptosis in septic polymorphonuclear neutrophils. Inhibition of apoptosis by PBEF is associated with reduced activity of caspases-8 and -3, but not caspase-9. These data identify PBEF as a novel inflammatory cytokine that plays a requisite role in the delayed neutrophil apoptosis of clinical and experimental sepsis.