Binding of Glucocorticoid-Receptor Complex to Rat Liver Nuclei and Chromatin of Various Ploidies

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A refractoriness of livers from fetal and immature rats to glucocorticoid action on tyrosine aminotransferase has been found. To investigate the age-related responsiveness to the hormone, the binding capacity of liver cytosol receptor to cortisol and the nuclear binding to the cortisol-cytosol receptor complex were measured in relation to the change in ploidy pattern. The proportion of diploid nuclei in isolated liver cell nuclei decreased abruptly to give rise to polyploid, mainly tetraploid nuclei between 2 and 6 weeks after birth, while the binding capacity of liver cytosol to ³H-cortisol increased gradually. In livers from15week-old rats, the binding capacity decreased. Adrenalectomy 5 days prior to the experiment resulted in a clear increase in the cytosol binding capacity of livers from9week-old rats, while corticosterone supplement to the rats for 5 days caused a marked decrease. When isolated liver nuclei were incubated with ³H-cortisol receptor complex prepared from livers of 9 week-old rats, the acceptor capacity of whole nuclei preparation from mature rats such as 6-, 9-and 15-week-old rats was about two-fold as large as that from immature rats (newborn and2-week-old). Adrenalectomy resulted in a slight increase in the nuclear binding capacity of livers from 9 week-old rats, while corticosterone supplement suppressed more or less the capacity. In contrast to this, the acceptor capacity of whole liver nuclei from rats at various ages was nearly negligible when the cortisol-receptor complex was replaced by free ³H-cortisol.
When isolated nuclei from6week-old rats were fractionated into diploid and polyploid classes, the acceptor capacity of polyploid nuclei to the cortisol-receptor complex was much larger than that of diploid nuclei. A similar difference was also observed when the chromatin preparations from nuclei of both ploidy classes were used, but in fact no binding was observed when the stripped DNA was substituted for nuclei or chromatin preparations. Biochemical analyses of protein and DNA of liver nuclei from rats at various ages revealed that there was no difference between protein concentrations per DNA except that of newborn rats, but polyploid nuclei chromatin was lacking in some nonhistone protein and a part of H1histone. A possible implication of the ploidy change in the glucocorticoid action was discussed in relation to the present findings.