Similar to PTX3, BDNF promoted bone metastatic gastric cancer–OB interactions (Figure 3F, white bars at left, P <0.05); however, the blockade of TrkB activation by either K252a (Figure 3F, gray bars at right, P <0.05) or TrkB specific small interfering RNA (siRNA) (Figure 3H, gray bars at right, P <0.05) hindered the BDNF-induced interactions of these cells, thereby indicating the requirement of TrkB activation in this interaction. The gene discussed is BDNF; the disease is gastric cancer.