FIGURE 5.

STAT3 activation is independent of tyrosine residues and not sufficient for cell proliferation. A, deletion variants of the murine IL-23R were generated by PCR. The first amino acid of the missing part of the IL-23R cytoplasmic domain is mentioned (e.g. Δ415). The postulated SHP2 binding site Tyr-416 or Tyr-397 was deleted, and a mutant variant with four Tyr → Phe substitutions was made. B, respective stably transduced Ba/F3-gp130 cells were generated as described and analyzed as mentioned. The Western blot data derived from different membranes and are therefore separated by black lines. Data are representative of at least two independent experiments. C, the colorimetric CellTiter-Blue® cell viability assay was used to determine the proliferation of the stably transduced Ba/F3-gp130 cell lines as mentioned. Values represent the mean value of three repetitions and were normalized. For comparison, n-fold proliferation was calculated by setting the negative control of each Ba/F3 cell line to a value of 1. Data are representative of at least two independent experiments. Error bars, S.D.