Fusion of FGFR1OP2 to FGFR1 in the KG-1 cell line. (A) Western blot analysis of whole-cell lysates revealed constitutive tyrosine phosphorylation of STAT5 in the KG-1 cell line. Detection of phospho-STAT5 is shown in the top panel, and total STAT5 is shown below. (B) Detection of a truncated form of activated FGFR1 in KG-1 cells by Western blot. COS7 cells transfected with full-length FGFR1 were used as a control. (C) Schematic representation of FGFR1OP2, FGFR1, and FGFR1OP2-FGFR1 proteins. Arrowhead indicates the position of the breakpoint. (D) Detection of FGFR1OP2-FGFR1, FGFR1OP2, and FGFR1 transcripts in the KG-1 and KG-1a cell lines.