Desmoglein 3 in apoptotic keratinocytes: participation of MAPK pathway, caspase 3, and metalloproteinase 9

Desmoglein 3 (Dsg3) is known to undergo proteolysis by caspases and matrix metalloproteinases (MMPs) during apoptosis, that associates with profound changes in ce11 shape and loss of intercellular contacts. Here we show that cells undergoing apoptosis may weaken their cohesion strength by acting on multiple molecular levels, such as transcriptional and translational regulation of molecules involved in cell adhesion, including Dsg3. First, we have demonstrated that induction of apoptosis in keratinocytes by staurosporine (STS) proceeds through the activation of the Raf-MEK-ERK pathway (death signal) as well as p38 MAPK phosphorylation. These changes were followed by reduction in the amount of surface Dsg3, as revealed by immunofluorescence microscopy, and paralleled with depletion of fulllength Dsg3 and its fragmentation by Western blotting. At the same time, Dsgl, Dsg2, and Ecadherin mRNA levels underwent slight down-regulation, as shown by RT-PCR analysis. Then, by using an in vitro essay, we were able to demonstrate the direct cleavage of Dsg3 by caspase 3. Furthermore, Western blot analysis and zymography revealed an increased matrix metalloproteinase (MMP)-9 protein expression and activity, respectively. Immunofluorescence studies confirmed the sustained secretion of MMP-9 within intercellular spaces upon induction of apoptosis. These changes paralleled with dramatic reduction of ce11 adhesion strength among keratinocytes, that was partially prevented in the presence of MMP inhibitors. However, we were unable to demonstrate the direct cleavage of Dsg3 by MMP-9. Overall, these data demonstrate that keratinocytes undergoing STS-induced apoptosis (a) activate MAPK pathway; (b) modulate transcription of cadherin genes; (C) process Dsg3 by caspase 3-activity (d) weaken intercellular cohesion strength through the action of MMPs, including MMP-9. Key ulouds: desmoglein 3, apoptosis, MAPK, MMP-9, caspase 3