Sequence of the 5'-flanking region of the gene encoding human muscle glycogen synthase

Impaired insulin-stimulated expression of the glycogen synthase gene in skeletal muscle of type 2 diabetic patients is acquired rather than inherited

To examine whether defective muscle glycogen synthase (GYS1) expression is associated with impaired glycogen synthesis in type 2 diabetes and whether the defect is inherited or acquired, we measured GYS1 gene expression and enzyme activity in muscle biopsies taken before and after an insulin clamp in 12 monozygotic twin pairs discordant for type 2 diabetes and in 12 matched control subjects. The effect of insulin on GYS1 fractional activity, when expressed as the increment over the basal values, was significantly impaired in diabetic (15.7 +/- 3.3%; P < 0.01), but not in nondiabetic (23.7 +/- 1.8%; P = NS) twins compared with that in control subjects (28.1 +/- 2.3%). Insulin increased GYS1 messenger ribonucleic acid (mRNA) expression in control subjects (from 0.14 +/- 0.02 to 1.74 +/- 0.10 relative units; P < 0.01) and in nondiabetic (from 0.24 +/- 0.05 to 1.81 +/- 0.16 relative units; P < 0.01) and diabetic (from 0.20 +/- 0.07 to 1.08 + 0.14 relative units; P < 0.01) twins. The effect of insulin on GYS1 expression was, however, significantly reduced in the diabetic (P < 0.003), but not in the nondiabetic, twins compared with that in control subjects. The postclamp GYS1 mRNA levels correlated strongly with the hemoglobin A1c levels (r = -0.61; P < 0.001). Despite the decrease in postclamp GYS1 mRNA levels, the GYS1 protein levels were not decreased in the diabetic twins compared with those in the control subjects (2.10 +/- 0.46 vs. 2.10 +/- 0.34 relative units; P = NS). We conclude that 1) insulin stimulates GYS1 mRNA expression; and 2) impaired stimulation of GYS1 gene expression by insulin in patients with type 2 diabetes is acquired and most likely is secondary to chronic hyperglycemia.

Cloning and characterization of a glycogen synthase cDNA from human endometrium

One major human uterine response to post-ovulatory progesterone is the accumulation of glycogen by the endometrium. A temporally related increase in glycogen synthase activity has been documented, but the isozyme responsible has not yet been identified. We have amplified a glycogen synthase (GS) complementary DNA (cDNA) from human endometrium by reverse transcription-polymerase chain reaction (RT-PCR). Overlapping clones of the PCR products provided a cDNA that is 3534 base pairs (bp) long, including a 22-bp poly(A)+ tail, and an open reading frame that encodes a 737 amino acid protein with a molecular weight of 83936. This cDNA is almost identical to that of human striated muscle GS. Differences include a double nucleotide substitution at 1983-1984 and five single nucleotide substitutions located, respectively, at positions 379, 2457, 2470, 2477, and 2553. These differences only alter the predicted amino acid sequence from that of the striated muscle protein by a single substitution at position 608. A 5'-end fragment plus an internal fragment of human myometrial GS cDNA were also analysed and were shown to have identity with the endometrial GS cDNA. Northern blot hybridization, using a human muscle-derived cDNA probe, detected the presence of a 4.0-kb GS messenger RNA (mRNA) in the endometrium and myometrium. Our results establish that the GS of human Mullerian tissues is, essentially, identical to that reported for human striated muscle.