Characterization of the AT[sub 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[sub 4] receptor. The peptide elicits a range of vascular and central actions including facilitation of memory retention and retrieval in several learning paradigms. The aim of this study was to characterize the AT[sub 4] receptor in a human cell line of neural origin. Receptor binding studies indicate that the human neuroblastoma cell line SK-N-MC cells express a high-affinity Ang IV binding site with a pharmacological profile similar to the AT[sub 4] receptor: [sup 125]I]-Ang IV and [sup 125]I]-Nle[sup 1]-Ang IV bind specifically to the SK-N-MC cell membranes (K[sub d] = 0.6 and 0.1 nm) in a saturable manner (B[sub max] = 1.2 pmol/mg of protein). AT[sub 4] receptor ligands, Nle[sup 1]-Ang IV, Ang IV and LVV-haemorphin 7 (LVV-H7), compete for the binding of [[sup 125]I]-Ang IV or [[sup 125]I]-Nle[sup 1]-Ang IV to the SK-N-MC cell membranes with rank order potencies of Nle[sup 1]-Ang IV > Ang IV > LVV-H7 with IC[sub 50] values of 1.4, 8.7 and 59 nm ([[sup 125]I]-Ang IV) and 1.8, 20 and 168 nm ([[sup 125]I]-Nle[sup 1]-Ang IV), respectively. The binding of [[sup 125]I]-Ang IV or [[sup 125]I]-Nle[sup 1]-Ang IV to SK-N-MC cell membranes was not affected by the presence of GTPγS. Both Ang IV and LVV-H7 stimulated DNA synthesis in this cell line up to 72 and 81% above control levels, respectively. The AT[sub 4] receptor in the SK-N-MC cells is a 180-kDa glycoprotein; under non-reducing conditions a 250-kDa band was also observed. In summary, the human neuroblastoma cell line, SK-N-MC, expresses functional AT[sub 4] receptors that are responsive 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 AT[sub 4] receptor. [ABSTRACT FROM AUTHOR]