Transforming growth factor-alpha: receptor binding and action on DNA synthesis in the sheep mammary gland.
Microsome factions prepared from the mammary glands of non-pregnant, pregnant and lactating sheep have been used to study binding of 125I-labelled transforming growth factor-alpha (TGF-alpha). Binding was dependent on microsomal protein concentration, time and temperature. It showed the characteristics of an epidermal growth factor (EGF) receptor, being displaced by TGF-alpha and EGF, but not by insulin or IGF-I. The non-linear curve fitting program LIGAND was used to determine affinity and number of binding sites. A single class of high-affinity binding sites was found. The apparent dissociation constant (Kd) was similar in all physiological states (2.43 +/- 0.27 mol/l x 10(-10), n = 23). Numbers of binding sites were lower in late-pregnant (20 weeks) and lactating sheep (14.07 +/- 2.45 fmol/mg protein, n = 10) than in non-pregnant, 10- or 15-week pregnant sheep (43.04 +/- 5.93 fmol/mg protein, n = 13). DNA synthesis by mammary alveolar epithelial cells cultured on collagen gels was increased twofold by TGF-alpha (maximum response at 10 micrograms/l; 1.8 nmol/l) but not by EGF. Cells derived from 15- to 20-week pregnant sheep responded significantly to TGF-alpha on day 3 of culture, but the response was delayed to day 4-5 of culture in cells from other physiological states. Dose-response was not significantly affected. TGF-alpha and IGF-I produced an additive effect on DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
Moorby
C D
CD
Department of Cellular Physiology, Babraham Institute, Cambridge, UK.
Taylor
J A
JA
Forsyth
I A
IA
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004848:Epithelium / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007774:Lactation / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D011485:Protein Binding; D012756:Sheep / Q000378:metabolism*; D013997:Time Factors; D016211:Transforming Growth Factor alpha / Q000378:metabolism* / Q000494:pharmacology
D016211:Transforming Growth Factor alpha; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D004247:DNA; D066246:ErbB Receptors