Relations between steroid-cell contact, steroid-binding and induction of tyrosine aminotransferase.
The induction of tyrosine aminotransferase by a variety of steroids was studied in cells from a hepatoma tissue culture (HTC). We have defined a class of steroids that induce TAT synthesis to a higher level than optimal inducers described earlier; these are called supra-inducers. When TAT induction is compared with the binding of the steroids to the cytoplasmic receptor or to their binding in the whole cell, a good correlation between binding in vivo of the hormone and its induction capacity can be established, whereas such a correlation was not systematically observed in vitro. A very short exposure of HTC cells to either dexamethasone or corticosterone is sufficient to induce TAT. When the inducer is removed from the culture medium a few minutes after its administration, the intracellular hormone concentration decreases very rapidly but TAT will be synthesized at its maximal rate. Thus the hormones behave as a starting signal for the optimal synthesis of the enzyme, and their presence in the culture medium is not necessary throughout the entire induction period.
D000818:Animals; D003345:Corticosterone / Q000378:metabolism; D046508:Culture Techniques; D003907:Dexamethasone / Q000378:metabolism; D004790:Enzyme Induction; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D011987:Receptors, Steroid / Q000378:metabolism; D013256:Steroids / Q000378:metabolism*; D014444:Tyrosine Transaminase / Q000096:biosynthesis*
D011987:Receptors, Steroid; D013256:Steroids; D003907:Dexamethasone; D014444:Tyrosine Transaminase; D003345:Corticosterone