Effects of suppression of CTSB on tumor xenograft growth in vivo. (A) The A549 cells were transfected with CTSB-shRNA as described in Materials and Methods. The protein level of CTSB was significantly down-regulated in A549 cells by CTSB-shRNA plasmids. (B) Tumor growth curve and tumor weight after treatment with CTSB-shRNA. No statistically significant difference between CTSB-shRNA treated group and the controls was observed (P > 0.05). The animal experiment was repeated three times. (C & D) TUNEL assay and PCNA staining. Suppression of CTSB showed no difference in cell proliferation and apoptosis in vivo. CTSB-shRNA treated tumor did not show significantly higher percentage of TUNEL-positive nuclei than tumors treated with PBS, Lipo, or NC (6 ± 1.3 versus 6 ± 1, 7 ± 1.5, or 7.5 ± 1.6, 6 ± 1.6) (P > 0.05). The rate of PCNA-positive nuclei in the four groups reached 93.4 ± 6.42, 89.6 ± 7.09, 85.6 ± 9.73, 82.0 ± 7.13 for PBS, Lipo, or NC, CTSB-shRNA, respectively (P > 0.05).