Expression of the human interleukin 6 receptor alpha-chain in Xenopus laevis oocytes

We investigated the biochemical properties of the 80 kDa binding subunit (gp80) of the human interleukin 6 receptor (IL-6R) in the genetic environment of the amphibian Xenopus laevis. In vitro transcribed mRNA encoding full length human gp80 was microinjected into Xenopus laevis stage VI oocytes. Protein expression was monitored by iodinated IL-6 and human gp80-specific monoclonal antibodies (mAb) PM1 and MT18. Maximal IL-6 binding activity was observed between 36-42 h after injection. Scatchard analysis indicated that gp80-injected oocytes expressed two independent classes of IL-6 binding sites of high- (Kd1 = 9 x 10(-11) M, 20 x 10(6) sites/cell) and low-affinity (Kd2 = 2 x 10(-9) M, 70.3 x 10(6) sites/cell). PM1 but not MT18 completely inhibited IL-6 binding to injected eggs. Our data suggest that the human IL-6R alpha-subunit gp80 is sufficient to confer high- and low-affinity IL-6 binding to Xenopus laevis oocytes.