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Regulation of cell-cell communication in rat bone cells: the effect of phorbol esters
R Massass1, L Mittelman, R Korenstein
1Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, 69978 Tel-Aviv, Israel.
Abstract:
The skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent inhibitor of gap junctional intercellular communication. In the present study, the inhibition of cell-cell communication by TPA has been investigated in primary bone cells from newborn rat calvaria, with an emphasis on the involvement of intracellular pH (pH(i)) and cytosolic calcium ([Ca(+2)](i)) in this process. The results show that TPA (5 x 10(-)(8) M) caused a complete inhibition of intercellular communication within 40-60 min. The intercellular communication was fully restored after overnight incubation in the presence of TPA. This effect was found to be associated with an elevation of pH(i). However, neither an increase of pH(i) alone nor exposure to TPA, under conditions preventing pH(i)-shift, were found to affect intercellular communication. It is suggested that the inhibition of intercellular communication, in the presence of TPA, depends on the pH(i)-shift itself rather than on the absolute value of pH(i). In addition, elevation of cytosolic calcium by ionomycin led to the termination of intercellular communication after 30 min. This inhibitory effect was abolished when the cells were incubated for overnight with TPA and then intracellular calcium was elevated by the addition of ionomycin. These results indicate that shift of pH(i) and the increase of intracellular calcium are involved in repression of intercellular communication by TPA.
Insights
The skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits cell communication by altering intracellular pH and calcium levels. These changes are reversible, suggesting a dynamic role in regulating intercellular signaling in bone cells.
Area of Science:
- Cell Biology
- Biochemistry
- Toxicology
Background:
- 12-O-tetradecanoylphorbol-13-acetate (TPA) is a known skin tumor promoter.
- TPA potently inhibits gap junctional intercellular communication (GJIC).
- The mechanisms underlying TPA-induced GJIC inhibition require further elucidation.
Purpose of the Study:
- To investigate the role of intracellular pH (pH(i)) and cytosolic calcium ([Ca(+2)](i)) in TPA-mediated inhibition of GJIC.
- To examine the effects of TPA on primary bone cells from newborn rat calvaria.
- To determine if pH(i) shifts or calcium levels are key mediators of TPA's effect.
Main Methods:
- Primary bone cells from newborn rat calvaria were treated with TPA.
- Intracellular pH (pH(i)) and cytosolic calcium ([Ca(+2)](i)) levels were monitored.
- Intercellular communication was assessed using established assays.
Main Results:
- TPA (5 x 10(-8) M) completely inhibited GJIC within 40-60 minutes.
- TPA-induced inhibition was associated with an elevation of pH(i).
- Neither pH(i) elevation alone nor TPA without a pH shift affected GJIC.
- Elevated cytosolic calcium also inhibited GJIC, but this effect was abolished after overnight TPA incubation.
Conclusions:
- TPA-induced inhibition of GJIC in bone cells is dependent on a shift in intracellular pH.
- Increased intracellular calcium also contributes to the inhibition of intercellular communication by TPA.
- The findings suggest that TPA modulates GJIC through coordinated changes in pH(i) and [Ca(+2)](i).