Abstract
1. 1. We have used 1,25-dihydroxyvitamin D 3 (1,25-(OH) 2D 3) to investigate autoregulation of homologous receptor and the control of c- myc mRNA and protein expression in C3H/10T1/2 cells. 2. 2. 10 nM 1,25-(OH) 2D 3 stimulated 1,25-(OH) 2D 3 receptor (VDR) synthesis in both non-transformed C3H/10T1/2 C1 8 and in chemically transformed C3H/10T1/2 Cl 16 cells within 4 hr of treatment. Maximal induction was observed between 8 and 24 hr. 3. 3. Two VDR mRNA transcripts, 2.7 and 4.8 kb, were present in both cell types. There were parallel changes in VDR specific mRNA levels and cellular VDR concentration in the C3H/10T1/2 Cl 8 cells indicating that the increase in receptor concentrations was dependent on de novo mRNA synthesis. 4. 4. The increase in VDR mRNA concentration in the chemically transformed C3H/10T1/2 Cl 16 cells was maximal already at 4hr, preceding the maximal increase in receptor concentration by 4–6 hr. 5. 5. Analysis of c- myc mRNA levels also showed cell line specificity. 6. 6. The c- myc mRNA level increased 2.1-fold with 10 nM 1,25-(OH) 2D 3 treatment in C3H/10T1/2 Cl 8 cells after 12 hr while the C3H/10T1/2 C1 16 cells had maximal c- myc mRNA level after 1 hr. 7. 7. The relative amount of c- myc mRNA remained higher than that of unstimulated controls the next 10–12 hr in C3H/10T1/2 Cl 16 cells. 8. 8. The c- myc protein levels were not affected by 1,25-(OH) 2D 3 treatment in either cell line as detected by Western blot analysis. 9. 9. Our data suggest that 1,25-(OH) 2D 3 mediated induction of VDR does not require prior c- myc protein synthesis in the C3H/10T1/2 cells. 10. 10. We found, however, that 1,25-(OH) 2D 3 treatment caused increased levels of c- myc mRNA but with different kinetics in the two cell lines. 11. 11. Accumulation of VDR mRNA in the presence of cycloheximide suggested that de novo synthesis of protein factors was not required for transcriptional activation.
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