FIG. 4.

STAT3 is the predominant STAT activated by IL-6 in LNCaP cells. LNCaP cells were cultured in T-medium plus 5% FBS and either not treated or treated with 2 nM IL-6 for 20 min. Cytosolic lysates (500 μg) were immunoprecipitated (IP) with antibodies to STAT1 (lanes 1 and 2), STAT3 (lanes 3 and 4), STAT5a (lanes 5 and 6), and STAT5b (lanes 7 and 8) and subjected to immunoblot analysis (WB) with antiphosphotyrosine (anti PY) antibody (A) and antibodies against the cognate STAT proteins (B). The antiphosphotyrosine immunoblot is shown overexposed to demonstrate that phosphotyrosine could be detected only in STAT3 under these conditions. Numbers on the left are molecular masses in kilodaltons.