Figure 6.

Determination of STAT3 acticity in HT-29 xenograft tumors. (A) Left: Test by EMSA for the formation of specific complexes on the SIE m67 STAT recognition element. Extracts of HT-29-derived tumors from nude mice (1–4) were incubated with the radiolabelled probe and analyzed by native PAGE and autoradiography. Right: Identification of STAT3 in the DNA-protein complex from tumor “1” by incubation with a specific anti-STAT3 antibody as indicated. Positions of STAT3-containing complexes and the antibody-dependent supershifted complex are marked by arrows. (B) Histologic examination of an HT-29-derived xenograft tumor for STAT3 activity. Sections from a representative tumor induced by injection of HT-29 cells into nude mice were stained with hematoxilin/eosin (top) or immunoreacted with an antibody specific for STAT3 phosphorylated at tyrosine 705 (bottom). Typical sites of crypt-like structures and tumor tissues with substantial nuclear concentration of activated STAT3 are indicated by arrows.