Diversity of B2 bradykinin receptors with nanomolar affinity expressed in passaged IMR90 human lung fibroblasts.
IMR90 human fetal lung fibroblasts express bradykinin receptors activating the pathway for biosynthesis of PGE2. A receptor of the B2 subtype stimulates half-maximal PGE2 production at 4.8 nM bradykinin, and maximal output takes place at 25 nM bradykinin. Radioligand binding studies reveal a population of [3H]bradykinin binding sites whose affinity correlates with this B2 receptor's biologic activity, with a KD of 2.5 nM. As IMR90 cells reach 60% of their defined life span in culture, they spontaneously induce expression of a second site of lower affinity, with half-maximal binding of [3H]bradykinin at 44 nM. This second site displays a characteristic primary B2 receptor recognition profile, but differs from the 2.5 nM site on a secondary level in recognition among different B2 ligands. Bradykinin is the most potent ligand at both sites; they each preferentially recognize an N-terminal extended bradykinin peptide construct having selectivity for the rat myometrial B2 receptor, suggesting that both sites have structural features in common. However, they display diversity in their order of preference for Met-Lys-bradykinin versus Lys-Lys-bradykinin; at the 44 nM site this order is completely reversed from the order of potency exhibited at the 2.5 nM site. Expression of the second site changes the manner in which these fibroblasts control their PGE2 production; it affords a graded response of PGE2 production at bradykinin levels beyond those which would normally saturate the 2.5 nM site. The inducibility of the 44 nM site in cultured fibroblasts addresses in vivo conditions in an inflammatory environment where continuing generation of bradykinin-related peptides takes place and presents a possible mechanism for overriding constraints that would otherwise limit the progression of inflammation.
Baenziger
N L
NL
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110.
Jong
Y J
YJ
Yocum
S A
SA
Dalemar
L R
LR
Wilhelm
B
B
Vavrek
R
R
Stewart
J M
JM
D000595:Amino Acid Sequence; D001920:Bradykinin / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D015232:Dinoprostone / Q000096:biosynthesis; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007705:Kinins / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D008168:Lung / Q000378:metabolism; D008969:Molecular Sequence Data; D011869:Radioligand Assay; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*
D007705:Kinins; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter; D015232:Dinoprostone; D001920:Bradykinin