Figure 3.

Confirmation by immunoblotting (bottom row) of the sst₂ expression detected with sst₂ immunohistochemistry (top row) in tumor samples of octreotide-treated patients (patients 1, 5b, and 3a) compared with controls consisting of sst₂-expressing HEK293 cells (HEK-sst₂) and a tumor sample from a patient not treated with octreotide (patient 15). In the immunoblot, a broad band centered around 70 kDa is stained by the R2-88 antiserum in all tested samples. This staining is completely abolished by preadsorption of R2-88 with the antigen peptide (a.p.). The variation in apparent molecular mass of the sst₂ receptor in the analyzed samples reflects the differences of glycosylation of the receptor. The positive sst₂ staining detected with the R2-88 antiserum in the immunohistochemistry samples of patients 1, 5b, and 3a as well as the membranous staining seen in the sample of patient 15 together with the presence of a sst₂ receptor band in all samples detected by R2-88 immunoblotting strongly suggests that the granular cytoplasmic structures seen by immunohistochemistry indeed correspond to the internalized sst₂ receptor. Pat., Patient.