Bax gene expression alters Ca(2+) signal transduction without affecting apoptosis in an epithelial cell line.
Bax is an oncogene that has proapoptotic properties but not all cells that express Bax undergo apoptosis. Bax may have a function unrelated to apoptosis. To elucidate the role of Bax in cell signaling, an epithelial cell line called SMG-C6 was transfected with the human bax gene. Stable transfectants were studied for their response to carbachol, a muscarinic receptor agonist, by measuring the increase in intracellular free Ca(2+) and Ca(2+) influx. Carbachol-mediated release of Ca(2+) from intracellular stores was significantly higher in Bax transfectants compared to control transfectants (empty vector). Ca(2+) influx was also increased in Bax transfectants. Bax had no affect on the storage operated channels. However, the concentration of Ca(2+) in the intracellular stores (i.e., mitochondria and granules) was 40-50% lower in the Bax transfectants. There was no significant difference in thapsigargin-mediated apoptosis in Bax transfectants compared to wild-type and control transfectants. Measurement of glutathione was reduced in the Bax transfectant. Restoration of glutathione levels with glutathione monoethyl ester partially normalized Ca(2+) mobilization and storage capacity in the mitochondria to control levels. This study shows that sub-apoptotic levels of Bax can reduce Ca(2+) content in intracellular stores and Ca(2+) homeostasis. Bax may mediate these effects by reducing the levels of antioxidants resulting in mild oxidative stress.
Aiba-Masago
Sonomi
S
Department of Community Dentistry, University of Texas Health Science Center, San Antonio, Texas, TX 78229-3900, USA.
Liu Xb
Xiao-bing
XB
Masago
Rejei
R
Vela-Roch
Norma
N
Jimenez
Fabio
F
Lau
Che-Ming A
CM
Frohlich
Victoria C
VC
Talal
Norman
N
Dang
Howard
H
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D018384:Oxidative Stress; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D000935:Antifungal Agents; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C494828:Bax protein, rat; C494813:Bcl2l1 protein, rat; D018679:Cholinergic Agonists; D007476:Ionophores; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011976:Receptors, Muscarinic; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D015759:Ionomycin; D019284:Thapsigargin; D002217:Carbachol; D008985:Monensin; D005978:Glutathione; D002118:Calcium