Fig. 4

Crosslinking of ¹²⁵I-IL-4 to IL-4 receptors on breast carcinoma cells. (A) MDA-MD231 and MCF-7 cells (5 × 10⁶) were incubated with ¹²⁵I-IL-4 in the absence (lanes 1 and 4) or presence of excess unlabeled IL-4 (lanes 2 and 5) for 2 hr at 4°C. In both these cell lines ¹²⁵I-IL-4 crosslinked receptors were immunoprecipitated with anti-IL-4 receptor antibody (M-7) (lanes 3 and 6). (B) MCF-7 cells were also crosslinked with radiolabeled IL-4 in the absence (lane 1) and presence of excess of IL-13 (lane 2) or IL-4 (lane 3). Bound ¹²⁵I-IL-4 was cross-linked to IL-4R with disuccinimidyl suberate (DSS). The cells were then lysed at 4°C with modified RIPA buffer. The resulting lysate was analyzed by electrophoresis through an SDS-PAGE (7%) gel. The gel was dried and exposed to an X-ray film for 7 days at −80°C. The molecular weight markers are shown on the left. The positions of different receptor chains are indicated. The dark area in lane 3 (B) represents autoradiography exposure artifact.