Untersuchungen zur Regulation der Zell-Zell-Kommunikation durch Degradation und posttranslationale Modifizierung der Connexine

Abstract

Communication through Gap Junctions could be regulated by multiple mechanisms. In this work the role of degradation of connexins as a mean to modulate communication was investigated. Furthermore the influence of phosphorylation of connexins on communication was analysed.<br /> Regulation of communication by degradation of connexins implies that cells have to be able to modulate the half-live of connexins.<br /> It was shown that the expression pattern of connexins influences their degradation rate. At least some connexins could stabilise others at protein-level. The half-life of connexin26 (cx26) could be prolonged by co-expression of connexin32 (cx32) and connexin45 (cx45) could be stabilised by co-expression of connexin43 (cx43).<br /> Degradation of cx26 and cx32 involves both proteasomes and lysosomes. The use of either lysomal or proteasomal degradation-inhibitors results in an increased coupling of cx26-expressing cells. Inhibition of lysosomes but not proteasomes increased the coupling of cx32-expressing cells. These results showed that communication through gap junctions could be up-regulated by a prolonged degradation-rate.<br /> Experiments with ³¹p-labelled cells revealed that the different influence of degradations-inhibitors of coupling via cx32-expressing cells was caused by dephosphorylation of cx32 in cells where lysosomal activity was blocked.<br /> A typical feature of glioma-cells is reduced coupling caused by low amounts of cx43 compared to astrocytes. Using two glioma cell-lines it was demonstrated that not only the amount of expressed connexin but also the phosphorylation-pattern influences cell-cell-commnication. Both cells-lines express cx43 at a similar level but showed great differences in coupling. Analysation of ³¹p-labelled cells showed that the phosphorylation-patterns of the expressed cx43 in both cells largely diverge from each other. This implies that the different phosporylated isoforms of cx43 cause the varying coupling.