Figure 2. (A) IL-6 activates STAT3, but not Erk, at high densities in Balb/c3T3 cells. IL-6 was added at 0, 10, 50, or 100 ng/mL for 15 min to Balb/c3T3 cells grown to 50% confluence (lanes 1–3), or 2 d postconfluence as indicated. Cell extracts were probed for STAT3-ptyr705 (upper panel) or Erk1/2 (lower panel), with tubulin or GAPDH as loading controls. Note the absence of Erk activation at high densities (lower panel, lanes 4 and 5). (B) IL-6 activates STAT3 and Erk in the absence of cadherin-11. Same as above, cadherin-11-deficient, Balb-shCad11 cells. Note the Erk activation at high densities (lower panel, lanes 3 and 4), same as STAT3, even at high densities (upper panel, 4 vs 6). (From ref. 20, reproduced with permission.)