Portal de Periódicos da CAPES

Thyroid Hormone Stimulation of Phosphorylation and Dephosphorylation of Rat Liver Cytosolic Proteins*

1983; Oxford University Press; Volume: 112; Issue: 2 Linguagem: Inglês

10.1210/endo-112-2-670

1945-7170

Hirotoshi Nakamura, Leslie J. DeGroot,

Metabolism, Diabetes, and Cancer

The effect of thyroid hormone on phosphorylation of the endogenous proteins in rat liver cytosol was investigated. Cytosolic proteins obtained from hypothyroid (H) and T3 (20 μg/100 g BW)-treated thyroidectomized (T) rats were incubated with [γ-32P]ATP at 30 C for 2 min, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiographic analysis. T3 given for 3 days increased the phosphorylation of 8–10 proteins. Two of these proteins were cAMP-dependent (mol wt, 60 and 47 × 103) and one was Ca2+ dependent (mol wt, 97 × 103). One protein with a mol wt of 43 × 103 showed significantly decreased phosphorylation. T3-induced changes in phosphorylation were detected 5 h after a single injection of T3. At this time, one protein (mol wt 39 × 103) showed increased phosphorylation, and another protein with a mol wt of 43 × 103 showed significantly decreased phosphorylation. The time course of dephosphorylation in vitro was more rapid for the 43 × 103 mol wt protein than for other proteins in T rats. Although dephosphorylation of the 43 × 103 mol wt protein was greater in T than in H rats, multifunctional phosphoprotein phosphatase activity measured with 32P-labeled protamine as a substrate did not differ between the groups. One of these T3-dependent phosphoproteins (mol wt, 60 × 103) was positively identified as pyruvate kinase by immunoprecipitation. After protein staining of the gels, the changes in the two proteins reflected the hormonal status of the animals. The concentration of a phosphoprotein with a mol wt of 220 × 103 was augmented in T rats. This increase was detected within 24 h. The quantity of a mol wt 67 × 103 protein was diminished by T3 injection for 3 days. These findings indicate that 1) phosphorylation in vitro of several endogenous proteins of rat liver cytosol is thyroid hormone dependent (although a direct T3 action has not been proved); 2) T3 effects on phosphorylation occur within 5 h; and 3) some T3-dependent phosphoproteins are important regulatory enzymes. The physiological signficance of the T3 effects on cytosolic phosphoproteins could be to control metabolism by regulating enzyme activities.