Proliferation of bovine undifferentiated mammary epithelial cells in vitro is modulated by G-proteins.
Several cAMP-elevating agents such as cholera toxin (CT), forskolin and 3-isobutyl-1-methylxanthine (IBMX) exhibited weak mitogenic activity on bovine undifferentiated mammary epithelial cells in three-dimensional collagen culture. CT and IBMX strongly synergized with epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) or both, but not with 10% fetal calf serum (FCS). Permeable cAMP analogs also synergized with IGF-I. Other hormones such as ovine prolactin, bovine growth hormone, estrogen or progesterone were not mitogenic and not synergistic with EGF, IGF-I, CT and FCS. Pertussis toxin (PT) reduced the DNA synthesis in cells cultured in the basal medium and attenuated 40-90% of the mitogenic activity stimulated by 10% FCS. PT inhibition of DNA synthesis was accompanied by ADP-ribosylation of 40 kDa and 41 kDa membrane proteins. The 41 kDa protein cross-reacted with antibodies that recognize the Gi-protein of the adenylate cyclase system, indicating the involvement of the latter in the mitogenic process. The nature of the second protein remains unknown. The present results suggest that the mitogenesis of normal mammary epithelial cells which is stimulated by IGF-I, EGF and other factors found in FCS is mediated through both cAMP-dependent and independent pathways. These pathways include PT-sensitive GTP-binding proteins.
Shamay
A
A
Department of Biochemistry and Human Nutrition, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel.
Pines
M
M
Waksman
M
M
Gertler
A
A
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000818:Animals; D001769:Blood; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D004247:DNA / Q000096:biosynthesis; D004357:Drug Synergism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology*; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D007328:Insulin; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D000246:Adenosine Diphosphate Ribose; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D004247:DNA; D002772:Cholera Toxin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D015056:1-Methyl-3-isobutylxanthine