Liang C T, Barnes J, Hanai H, Levine M A
Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore 21224.
Am J Physiol. 1993 May;264(5 Pt 2):F770-3. doi: 10.1152/ajprenal.1993.264.5.F770.
The possibility that alteration in stimulatory guanine nucleotide-binding protein (Gs) expression may contribute to the blunting of renal parathyroid hormone (PTH)-stimulated adenylate cyclase in aged rats was examined. Using rat cDNA probe, we identified a Gs alpha-subunit (Gs alpha) of 1.9 kb. Age did not alter the size of Gs alpha mRNA. The level of Gs alpha mRNA [normalized to poly(A)+ RNA] was decreased 23%, which was consistent with our previous report that Gs alpha protein decreased in senescence. In contrast, mRNA level of Gi alpha 2 increased with age. Level of beta-actin mRNA did not change with age. Nuclear runoff assay was performed to determine the transcription rate of Gs mRNA. Synthesis of poly(A)+ RNA and total RNA was reduced 39% and 37%, respectively, in nuclei prepared from old kidney, which suggested a general decline in RNA synthesis capacity in old rats. Our results also showed the transcription rate of Gs alpha mRNA in aged rats was reduced 89%, a decrease far exceeding that observed for total RNA or poly(A)+ RNA. We concluded that the decrease in steady-state level of Gs alpha mRNA was specific and probably was due to a reduction in the transcription activity. Thus alteration in Gs transcription may contribute, at least in part, to the impaired renal adenylate cyclase activation in aged rats.
研究了刺激性鸟嘌呤核苷酸结合蛋白（Gs）表达的改变可能导致老年大鼠肾甲状旁腺激素（PTH）刺激的腺苷酸环化酶功能减弱的可能性。使用大鼠cDNA探针，我们鉴定出一个1.9 kb的Gsα亚基（Gsα）。年龄并未改变Gsα mRNA的大小。Gsα mRNA水平（以聚腺苷酸加尾RNA标准化）降低了23%，这与我们之前关于衰老过程中Gsα蛋白减少的报道一致。相比之下，Giα2的mRNA水平随年龄增加而升高。β-肌动蛋白mRNA水平不随年龄变化。进行核转录延伸分析以确定Gs mRNA的转录速率。从老年大鼠肾脏制备的细胞核中，聚腺苷酸加尾RNA和总RNA的合成分别减少了39%和37%，这表明老年大鼠的RNA合成能力普遍下降。我们的结果还表明，老年大鼠中Gsα mRNA的转录速率降低了89%，这一降低幅度远远超过了总RNA或聚腺苷酸加尾RNA的降低幅度。我们得出结论，Gsα mRNA稳态水平的降低是特异性的，可能是由于转录活性降低所致。因此，Gs转录的改变可能至少部分导致了老年大鼠肾腺苷酸环化酶激活受损。
