Upregulation of vasopressin V-1A receptor mRNA and protein in vascular smooth muscle cells following cyclosporin A treatment

1 The major side effects of the immunosuppressive drug cyclosporin A (CsA) are hypertension and nephrotoxicity. It is likely that both are caused by l ocal vasoconstriction. 2 We have shown previously that 20 h treatment of ra t vascular smooth muscle cells (VSMC) with therapeutically relevant CsA con centrations increased the cellular response to [Arg*]vasopressin (AVP) by i ncreasing about 2 fold the number of vasopressin receptors. 3 Displacement experiments using a specific antagonist of the vasopressin V -1A receptor (V1AR) showed that the vasopressin binding sites present in VS MC were exclusively receptors of the VIA subtype. 4 Receptor internalization studies revealed that CsA (10(-6) M)did not sign ificantly alter AVP receptor trafficking. 5 V1AR mRNA was increased by CsA, as measured by quantitative polymerase ch ain reaction. Time-course studies indicated that the increase in mRNA prece ded cell surface expression of the receptor. as measured by hormone binding . 6 A direct effect of CsA on the V1AR promoter was investigated using VSMC t ransfected with a V1AR promoter-luciferase reporter construct. Surprisingly , CsA did not increase. but rather slightly reduced V1AR promoter activity. This effect was independent of the cyclophilin-calcineurin pathway. 7 Measurement of V1AR mRNA decay in the presence of the transcription inhib itor actinomycin D revealed that CsA increased the half-life of V1AR mRNA a bout 2 fold. 8 In conclusion, CsA increased the response of VSMC to AVP by upregulating V1AR expression through stabilization of its mRNA. This could be a key mech anism in enhanced Vascular responsiveness induced by CsA, causing both hype rtension and. via renal vasoconstriction, reduced glomerular filtration.