Analysis of cell lines derived from in vivo tumors.

(A) Expression of various Abl proteins in tumor-derived cell lines by direct Western blotting with an antiserum that detects the various Abl transforming proteins. (B) Northern blot analysis of the expression of the Stat5a/b target genes, CIS and OSM. Cell lines derived from wild-type (wt) mice or mice heterozygous for Stat5a/b and cell lines from Stat5a/b-deficient tumors were examined. GAPDH is included as a loading control. (C) The extent of activation of various Stats was examined by immunoprecipitation with Stat-specific antibodies and Western blotting (WB) with a monoclonal antibody against phosphotyrosine (4G10). Antisera specific for Stat1, Stat3, and Stat5 were used. The smaller form of Stat5 seen in one of the Stat5a/b-deficient tumor cells represents the N-terminal truncated form that is produced from the disrupted locus as previously described.6