Objective:

Gap junctions which are formed by connexins (Cx) are intercellular channels enabling the communication between neighbouring cells. They are involved in the modulation of cell death and survival. The kind of signal transferred between cells after induction of apoptosis, and the question whether gap junctions or hemichannels are involved in the modulation of apoptosis are still unsolved. In this study we sought to clarify the role of hemichannels and the kind of signal spreading between cells after induction of apoptosis.

Methods and results:

Apoptosis (1/10 µM Streptonigrin or 100/200 ng/ml anti-Fas) was significantly increased (annexin V/PI; FACS) in HeLa cells expressing Cx43 (100ng/ml anti-Fas: 24 ± 4%) compared to Cx deficient HeLa cells transfected with an empty vector (LV; 100ng/ml anti-Fas: 5 ± 1%). Apoptosis induced by Streptonigrin (SN) or anti-Fas led to an increase of the apoptotic cleavage of caspase 7 and Parp when Cx43 was expressed. Inhibition of gap junctional communication (meclofenamic acid and heptanol) reduced apoptosis (untreated: 6.4 ± 0.6%; 1µM SN: 15.5 ± 4.7 %; 100 ng/ml anti-Fas: 24.0 ± 3.6%; 1µM SN+MH: 7.1 ± 0.4%; 100 ng/ml anti-Fas+MH: 11.8 ±1.1%) whereas inhibition of hemichannels (50µM specific Cx43 blocking peptide) which had no influence on gap junctional communication did not affect the rate of apoptosis. Incubation with SN led to a Ca²⁺ increase within 3 min in nearly all Cx expressing cells (99 ±1%) which was reduced to 36 ± 12% after blocking the IP₃ receptor (40µM xestospongin-C) or by blocking gap junctions.

Conclusion:

Apoptosis induced by SN or anti-Fas is enhanced by gap junctional communication suggesting that the exchange of pro-apoptotic signals via intercellular channels plays an important role. One of the signals passing the gap junctions could be IP₃.