FIGURE 6.

Re-expression of Fos enhanced the tumor formation. A, re-expression of Fos in PRIP^-/- cells. PRIP^-/- cells stably re-expressing FOS were established by transfecting PRIP^-/- with FOS expression vector. The FOS mRNA levels were measured by real time RT-PCR. Two clones (F1 and F2) expressed FOS mRNA at a level similar to that of wild type cells (WT). PRIP^-/- cells integrated with an empty vector served as a control (KO). B, wild type tumor cells, control PRIP^-/- tumor cells, and clones re-expressing FOS (F1 and F2) (1 × 10⁶ cells) were injected into nude mice. The experiment was performed in triplicate, and tumor sizes were measured. The tumors formed by PRIP^-/- tumor cells were much smaller than those from wild type tumor cells and PRIP^-/- tumor cells re-expressing Fos (F1 and F2). a, representative tumors formed by injected tumor cells. b, average tumor sizes were calculated.