Connexin32 hemichannels contribute to the apoptotic-to-necrotic transition during Fas-mediated hepatocyte cell death

Abstract

The present study was set up to investigate the fate of connexin32 and its channels in hepatocellular apoptosis. Primary hepatocyte cultures were exposed to Fas ligand and cycloheximide, and modifications in connexin32 expression and localization, and gap junction functionality were studied. We found that gap junction functionality rapidly declined upon progression of cell death, which was associated with a decay of the gap junctional connexin32 protein pool. Simultaneously, levels of newly synthesized connexin32 protein increased and gathered in a hemichannel configuration. This became particularly evident towards the end stages of the cell death process and was not reflected at the transcriptional level. We next either silenced connexin32 expression or inhibited connexin32 hemichannel activity prior to cell death induction. Both approaches resulted in a delayed termination of the cell death response. We conclude that connexin32 hemichannels facilitate the apoptotic-to-necrotic transition, which typically occurs in the final stage of hepatocellular apoptosis.

Connexin 43 Hemichannels Contribute to Cytoplasmic Ca2+ Oscillations by Providing a Bimodal Ca2+-dependent Ca2+ Entry Pathway

“…When BKtriggered oscillations were elicited in the presence of the general connexin channel blocker Cbx (25 M, 30-min preincubation and present during the 10-min observation window), the initial Ca 2ϩ spike remained, but the subsequent oscillations disappeared. We further applied two peptide connexin channel inhibitors, 32 Gap27 and 43 Gap26, that target Cx32 and Cx43 channels, respectively (36,48). Application of 32 Gap27/ 43 Gap26 ("Gap," 200 M, 30-min preincubation and present during the recording) also inhibited the Ca 2ϩ oscillations without perturbing the initial peak (Fig.…”

Modifications in Connexin Expression in Liver Development and Cancer

“…It has been suggested that these colocalised modifi cations in the expression of cytochrome P450 isoenzymes and Cx32 refl ect a defence mechanism to restrict the intercellular diffusion of reactive intermediates produced through xenobiotic biotransformation (Neveu et al, 1994). Furthermore, gap junctions, particularly those composed of Cx32, also act as goalkeepers of other aspects of the hepatocyte life cycle, including cell growth (Vinken et al, 2008) and apoptotic cell death (Vinken et al, 2010).…”

Emerging roles of connexin hemichannels in gastrointestinal and liver pathophysiology

“…Our group was the first to report the occurrence of Cx32 hemichannels in hepatocytes. Using an in vitro model of Fas-mediated apoptosis, a cell death mode involved in most liver pathologies, we found that de novo synthesized Cx32 gathers in hemichannels during apoptosis, and that hemichannel opening is critical for the termination of the cell death response [20] .…”