Effect of Na + flux inhibitors on induction of c-fos, c-myc, and ODC genes during cell cycle.
The role of Na + transport systems in the mitogenic signal induced by growth factors was studied, and it was shown that two Na + transport systems contribute to the early increase in cytoplasmic Na + in response to serum growth factors, namely the amiloride-sensitive Na+/H+ antiport and the bumetanide-sensitive Na+/K+/Cl- cotransport. Bumetanide or amiloride, when added separately, inhibited part of the increase in cytoplasmic Na +, as a response to the addition of serum to quiescent BALB/c mouse 3T3 fibroblasts. Each drug also suppressed part of the stimulation of the ouabain-sensitive Rb + influx, which was controlled by intracellular Na +. However, when both drugs were added together with serum growth factors, a complete inhibition of the early increase in [Na +], and subsequently a complete blockage of Na+/K+ pump stimulation was obtained. Amiloride or bumetanide, when added separately, only partially inhibited DNA synthesis induced by serum, 24% and 8% respectively. However, when both drugs were added together, at the time of serum addition to the quiescent cells, cell entry into S-phase was completely inhibited. To investigate the mode of cell-cycle inhibition, analysis was done of the possible role of early Na + fluxes in the mitogenic signal transduced from cell membrane receptors to the nucleus. The effects of the two drugs amiloride and bumetanide on induction of three genes--c-fos, c-myc, and ornithin decarboxylase (ODC)--was measured during cell transition through the G1-phase. Amiloride and bumetanide, when added separately or in combination, did not inhibit the induction of c-fos, c-myc, and ODC mRNAs. These results suggest that stimulation of Na + fluxes by serum growth factors is essential for cell transition into the S-phase of cell cycle, but it plays no apparent role in the growth factor signal transduced from the cell surface to the interior of the cell, as manifested by c-fos, c-myc, and ODC genes induction.
Panet
R
R
Department of Medical Biophysics and Nuclear Medicine, Hadassah University Hospital, Jerusalem, Israel.
Amir
I
I
Snyder
D
D
Zonenshein
L
L
Atlan
H
H
Laskov
R
R
Panet
A
A
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015152:Blotting, Northern; D002034:Bumetanide / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000166:cytology; D051379:Mice; D008807:Mice, Inbred BALB C; D009955:Ornithine Decarboxylase / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos; D016271:Proto-Oncogene Proteins c-myc; D012313:RNA / Q000032:analysis; D012964:Sodium / Q000378:metabolism*
D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D016271:Proto-Oncogene Proteins c-myc; D002034:Bumetanide; D012313:RNA; D000584:Amiloride; D012964:Sodium; D009955:Ornithine Decarboxylase