Truncated isoforms inhibit [3H]prazosin binding and cellular trafficking of native human alpha1A-adrenoceptors

Biochem J. 1999 Oct 1;343 Pt 1(Pt 1):231-9.

Abstract

We have identified from human liver eight alpha(1A)-adrenoceptor (alpha(1A)-AR) splice variants that were also expressed in human heart, prostate and hippocampus. Three of these alpha(1A)-AR isoforms (alpha(1A-1)-AR, alpha(1A-2a)-AR and alpha(1A-3a)-AR) gave rise to receptors with seven transmembrane domains (7TMalpha(1A)-AR). The other five (alpha(1A-2b)-AR, alpha(1A-2c)-AR, alpha(1A-3c)-AR, alpha(1A-5)-AR and alpha(1A-6)-AR) led to truncated receptors lacking transmembrane domain VII (6TMalpha(1A)-AR). The 7TMalpha(1A)-AR isoforms transiently expressed in COS-7 cells bound [(3)H]prazosin with high affinity (K(d) 0.2 nM) and mediated a noradrenaline (norepinephrine)-induced increase in cytoplasmic free Ca(2+) concentration, whereas the 6TMalpha(1A)-AR isoforms were incapable of ligand binding and signal transduction. Immunocytochemical studies with N-terminal epitope-tagged alpha(1A)-AR isoforms showed that the 7TMalpha(1A)-AR isoforms were present both at the cell surface and in intracellular compartments, whereas the 6TMalpha(1A)-AR isoforms were exclusively localized within the cell. Interestingly, in co-transfected cells, each truncated alpha(1A)-AR isoform inhibited [(3)H]prazosin binding and cell-surface trafficking of the co-expressed 'original' 7TMalpha(1A-1)-AR. However, there was no modification of either the [(3)H]prazosin-binding affinity or the pharmacological properties of alpha(1A-1)-AR. Immunoblotting experiments revealed that co-expression of the alpha(1A-1)-AR with 6TMalpha(1A)-AR isoforms did not impair alpha(1A-1)-AR expression. Therefore the expression in human tissues of many truncated isoforms constitutes a new regulation pathway of biological properties of alpha(1A)-AR.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport
  • Blotting, Western
  • COS Cells
  • Cloning, Molecular
  • DNA, Complementary
  • Humans
  • Liver / metabolism
  • Molecular Sequence Data
  • Prazosin / antagonists & inhibitors*
  • Prazosin / metabolism
  • Protein Binding
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism*
  • Radioligand Assay
  • Receptors, Adrenergic, alpha-1 / chemistry
  • Receptors, Adrenergic, alpha-1 / genetics
  • Receptors, Adrenergic, alpha-1 / metabolism*
  • Sequence Homology, Amino Acid
  • Subcellular Fractions / metabolism
  • Tritium

Substances

  • ADRA1A protein, human
  • DNA, Complementary
  • Protein Isoforms
  • Receptors, Adrenergic, alpha-1
  • Tritium
  • Prazosin