Fig. 1. Osteopontin is regulated by OBF1 in lymphoid cells. (A) Analysis of OPN expression in wild-type (wt) and OBF1–/–(ko) splenocytes. Cells were stimulated in vitro and total RNA was analyzed by northern blotting. Osteopontin (OPN) transcripts were found at high levels in wild-type splenocytes. OBF1–/– splenocytes show reduced OPN transcript levels. Actin, control for comparable mRNA levels in both samples; OBF1, control to show the presence of transcripts in wild-type cells and absence in knockout cells. (B) Comparison of enhancer activities of PORE-derived elements in transient transfection experiments. BJA-B cells were transfected with different luciferase reporter plasmids (x-axis). The y-axis shows activation of transcription, expressed as relative luciferase activities. The tk minimal promoter served as a control. BJA-B cells naturally express OBF1. PORE^D and PORE^M are derivatives of the PORE, to which only the POU dimer and monomer, respectively, can bind.