Differences in desensitization between human β₁- and β₂-adrenergic receptors stably expressed in transfected hamster cells

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• 作者：Zhou ; Xiao-Ming ; Pak ; Michael ; Wang ; Ziyuan ; Fishman ; Peter H.
• 关键词：β ; -adrenergic receptors ; desensitization ; adenylyl cyclase ; protein kinase A ; receptor kinase
• 刊名：Cellular Signalling
• 出版年：1995
• 出版时间：March, 1995
• 年：1995
• 卷：7
• 期：3
• 页码：207-217
• 全文大小：752 K

文摘

It is well-established that agonist-mediated desensitization of the β₂-adrenergic receptor (β₂AR) involves its phosphorylation by protein kinase A (PKA) and the βAR kinase (βARK). The phosphorylated receptor is less efficient at mediating agonist stimulation of adenylyl cyclase activity. The result is an increase in the concentration of agonist required for half-maximal stimulation (ec₅₀) and a reduction in maximal stimulation (V_max). As less is known about desentization of the human β₁AR, we compared the desensitization pattern of human β₁AR and β₂AR stably expressed in two different hamster cell lines: Chinese hamster ovary (CHO), and Chinese hamster fibroblast (CHW). Following agonist treatment, all of the cell lines exhibited an increase in ec₅₀, and a reduction inV_max was observed in CHO-β₂ but not β₁ cells. CHW-β₁ cells were resistant to acute agonist-mediated reduction inV_max compared to CHW-β₂ cells. More prolonged agonist exposure produced a modest reduction in V_max and this effect was more noticeable when the CHW cells expressed lower levels of β₁AR. To explore the role of protein kinases in these effects, digitonin-permeabilized CHW cells were loaded either with heparin (a βARK inhibitor) or a peptide inhibitor of PKA and exposed to agonist. In both β₂AR- and β₁AR-expressing cells, heparin inhibited the reduction in V_max and the PKA inhibitor blocked the increase in ec₅₀. Finally, exposing CHW cells expressing either subtype to a permeable cyclic AMP derivative caused an increase in ec₅₀ similar to that observed in agonist-treated cells, but without any reduction in maximal activity. Our data suggest that whereas PKA-mediated desensitization is not subtype-specific, human β₁AR is more resistant to βARK-mediated desensitization compared to the human β₂AR.