Characterization of the AT(4) receptor in a human neuroblastoma cell line (SK-N-MC)

Angiotensin IV (Ang IV), the 3-8 fragment of angiotensin II (Ang II), binds to a distinct receptor designated the AT(4) receptor. The peptide elicits a range of vascular and central actions including facilitation of memory re tention and retrieval in several learning paradigms. The aim of this study was to characterize the AT(4) receptor in a human cell line of neural origi n. Receptor binding studies indicate that the human neuroblastoma cell line SK-N-MC cells express a high-affinity Ang IV binding site with a pharmacol ogical profile similar to the AT(4) receptor: [I-125]-Ang IV and [I-125]-Nl e(1)-Ang IV bind specifically to the SK-N-MC cell membranes (K-d = 0.6 and 0.1 nM) in a saturable manner (B-max = 1.2 pmol/mg of protein). AT(4) recep tor ligands, Nle(1)-Ang IV, Ang IV and LVV-haemorphin 7 (LVV-H7), compete f or the binding of [I-125]-Ang IV or [I-125]-Nle(1)-Ang IV to the SK-N-MC ce ll membranes with rank order potencies of Nle(1)-Ang IV > Ang IV > LVV-H7 w ith IC50 values of 1.4, 8.7 and 59 nM ([I-125]-Ang IV) and 1.8, 20 and 168 nM ([I-125]- Nle(1)-Ang IV), respectively. The binding of [I-125]-Ang IV or [I-125]-Nle(1)-Ang IV to SK-N-MC cell membranes was not affected by the pr esence of GTP gammaS. Both Ang IV and LVV-H7 stimulated DNA synthesis in th is cell line up to 72 and 81% above control levels, respectively. The AT(4) receptor in the SK-N-MC cells is a 180-kDa glycoprotein; under nonreducing conditions a 250-kDa band was also observed. In summary, the human neurobl astoma cell line, SK-N-MC, expresses functional AT(4) receptors that are re sponsive to Ang IV and LVV-H7, as indicated by an increase in DNA synthesis . This is the first human cell line of neural origin shown to express the A T(4) receptor.