Background & objective: STAT3 protein has been found constitutively activated in a wide variety of human tumor tissues and cell lines. It may be involved in tumorigenesis and development. This study was to observe the activation of STAT3 protein in mouse melanoma cell line B16, human liver cancer cell lines SMMC-7721 and HepG-2, human lung cancer cell line A549, and human cervical cancer cell line HeLa, and to investigate the effects of STAT3 antisense oligodeoxynucleotides (ASODN) on proliferation and apoptosis of B16 cells.
Methods: B16 cells were transfected with STAT3 ASODN or STAT3 sense oligodeoxynucleotides (STAT3 SODN), respectively. The expression and phosphorylation levels of STAT3 protein in all the tumor cells were measured by Western blot. The proliferation of B16 cells was detected by MTT assay. Cell apoptosis was determined by Hoechst33258 staining and Annexin V/PI using flow cytometry.
Results: STAT3 was highly expressed and phosphorylated in all the tumor cells. Transfection of STAT3 ASODN suppressed the expression and phosphorylation levels of STAT3 protein in B16 cells. Forty-eight hours after transfection, the proliferation of B16 cells was inhibited the higher the concentration (0-200 nmol/L) of STAT3 ASODN was, the heavier the inhibition was (P<0.01); when transfected with STAT3 SODN over 250 nmol/L, the proliferation of B16 cells was also inhibited (P<0.05). Inhibitory effects appeared 24 h later after transfection of STAT3 ASODN, and became more obvious 48 h later (P<0.01). The early apoptosis rate was significantly higher in 400, 800, 2,000 nmol/L STAT3 ASODN groups and 2,000 nmol/L STAT3 SODN group than in blank control group (8.22%, 9.99%, 16.97%, and 13.31% vs. 5.52%, P<0.01); no significant difference was found among 400 and 800 nmol/L STAT3 SODN groups and blank control group (5.87%, 5.36% and 5.52%, P>0.05).
Conclusions: STAT3 is highly expressed and activated in all the tumor cells detected. STAT3 ASODN can abrogate the activity of STAT3 protein, inhibit proliferation and induce apoptosis of B16 cells, which support that STAT3 may be a potential molecular target for tumor therapy.