Objective: 

Connexins (Cx) are a family of membrane spanning proteins building specialized intercellular channels, which are known to modulate essential processes including the regulation of cell death and survival. Most effects on modulating survival and apoptosis are described for Cx43 and only a few studies show that also other Cx proteins may play a role in this context. In this study we sought to clarify whether and how the expression of different Cx influences the rate of apoptosis. Moreover, we studied whether this regulatory effect is dependent on functional gap junctions built by Cx.

Methods and results: 

Apoptosis (5mM H₂O₂ or 1mM streptonigrin) was significantly increased (annexin V/PI or JC-1; FACS) in HeLa cells expressing Cx40 or Cx43 compared to Cx deficient HeLa-wt or HeLa-Cx37 cells. The amount of apoptotic cells varied depending on the Cx expressed in the cells (HeLa-wt: 20±2%, HeLa-Cx37: 18±2%, HeLa-Cx40: 34±2% and HeLa-Cx43 45±3%) and correlated with GJ permeability as assessed by AlexaFluor488 spreading (Cx43>Cx40>Cx37). Prevention of GJ formation in HeLa-Cx43 cells (by culturing the cells for 12h in suspension) resulted in reduced SN-induced apoptosis and was comparable to apoptosis in adherent SN-treated HeLa-wt cells (HeLa-Cx43_sus: 49±5%, HeLa-wt 48±3%). Moreover, supernatants of SN-treated apoptotic HeLa-Cx43 cells did not induce apoptosis in neither HeLa-wt nor in HeLa-Cx43 cells indicating that a paracrine transfer of pro-apoptotic signals was not involved.

Conclusion: 

Apoptosis induced by SN is enhanced by the presence of connexins in HeLa cells. For the spreading of pro-apoptotic signals not only Cx but functional gap junctions built by the Cx are necessary.