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. 2011 Apr 23;60(5):1435–1445. doi: 10.2337/db10-1663

FIG. 6.

FIG. 6.

PPP1R3G modulates the activity of GS in coordination with the fasting–refeeding cycle. A and B: Liver GS and GP activities were measured from the samples as in Fig. 4A. Data are shown as mean ± SD. ***P < 0.001 between the two groups. C: Male C57BL/6 J mice at 8 weeks of age were infected with shRNA adenovirus as indicated via tail-vein injection. Seven days after infection, animals were killed in constant feeding state, after fasting, or after refeeding for the time as indicated (n = 4 or 5 mice/group). Liver GS activity is shown as mean ± SE. *P < 0.05 and **P < 0.01. The numbers above the bars of Ad-scrambled-shRNA group mark the actual GS activity. The numbers above the bars of Ad-PPP1R3G group represent the percentage decrease of GS activity in this group in comparison with the control group, respectively. D: Expression patterns of PPP1R3G and other glycogen-targeting regulatory subunits of PP1 in the liver during fasting and refeeding. The liver samples of mice (n = 4 mice/group) with fasting and refeeding for different amounts of time were used to determine the mRNA levels of PPP1R3B, 3C, 3D, 3E, and 3G by RT-qPCR. Data are shown as mean ± SD. *P < 0.05 and **P < 0.01 compared with the unfasted group. E: Simplified model to depict the expression patterns of glycogen-targeting regulatory subunits of PP1 in the liver during the fasting–feeding cycle and their roles in regulating GS activity and hepatic glycogenesis in mouse. Fasting increases PPP1R3G expression but decreases the expression of other glycogen-targeting regulatory subunits of PP1, including PPP1R3B, 3C, and 3D, whereas refeeding has an opposite effect. The combined effects of PPP1R3G together with other glycogen-targeting regulatory subunits of PP1 determine how these subunits contribute to GS activity and liver glycogenesis at different phases of the fasting–feeding cycle. Because of its unique expression pattern, PPP1R3G plays a major role in regulating hepatic glycogenesis during the fasting–feeding transition. For simplicity purposes, the expression pattern of PPP1R3E is not included because its expression level is not changed during the fasting–feeding cycle in the liver.