Ewing's sarcoma (ES) is a primary bone
tumor characterized by a chromosomic translocation between the EWS gene and a member of the ETS gene family, mainly FLI1, which leads to an aberrant
transcription factor EWS-FLI1 that promotes tumorigenicity. Gap junctions are intercellular channels composed of transmembrane
proteins (
connexin: Cx), that allow direct intercellular communication between adjacent cells. Numerous studies have shown that
tumorigenesis may be associated with a loss of gap junctional intercellular communication (GJIC). Loss of
Cx43 expression was observed at the
protein and
mRNA levels in ES cell lines compared to those measured in human mesenchymal stem cells. A673 ES cells stably transfected with an
shRNA targeting
EWS-FLI1 showed an increase in
Cx43 expression (at the
mRNA,
protein and transcriptional levels) and GJIC. In an osteolytic murine model of ES, the overexpression of
Cx43 in ES cells dramatically reduced
tumor growth, leading to a significant increase in animal survival. In vitro assays showed that
Cx43 overexpression increases the p27 level with an associated marked decrease of Rb phosphorylation, consistent with the observed blockade of the cell cycle in G0/G1 phase. In addition, the bone microarchitectural parameters, assessed by micro-CT analysis, showed an increased bone volume when
Cx43 expression was enhanced. Histological analysis demonstrated that the overexpression of
Cx43 in ES
tumor cells inhibits osteoclast activity and therefore
bone resorption. Our study demonstrated that the loss of
Cx43 expression in ES cells plays a crucial role in the development of the primary
tumor and the associated bone
osteolysis.