3.5 TA inhibits the STAT3 pathway in vivo
We previously showed that TA inhibited the proliferation and growth of
PANC-1 cells by down-regulating the expression levels of p-STAT3
(Tyr705) and STAT3-regulated proteins. To examine whether TA also
suppressed the biological functions of STAT3 in vivo , we first
evaluated the expression levels of total STAT3, p-STAT3 (Tyr705), and
STAT3-regulated proteins in the tumor tissues. As shown in Figure 5a, TA
evidently down-regulated the expression of p-STAT3 (Tyr705) and STAT3
downstream target proteins such as c-Myc, Survivin, and ICAM-1 in the
high-dose group (40 mg/kg/d), while had no remarkable effect on the
protein expression of total STAT3, Cyclin D1, and Bcl-2. Furthermore,
immunohistological analysis of tumor tissue sections also indicated that
the expression of p-STAT3 (Tyr705), c-Myc, Survivin, MMP-9, and ICAM-1
was markedly reduced in the TA-treated groups compared with the negative
control group (Figure 5b).
To further validate whether TA inhibited STAT3 signaling pathwayin vivo , the protein expression of p-STAT3 (Tyr705) was
determined by the tissue immunofluorescence staining. TA significantly
decreased the expression of p-STAT3 (Tyr705) protein in the tumor
tissues (Figure S8a). In addition, the mRNA expression levels of STAT3
target genes were measured by the qRT-PCR to examine whether TA had an
impact on the expression of STAT3 downstream genes in the tumor tissues.
TA dramatically decreased endogenous BCL2 , MYC ,VEGF , CASP3 , MMP9 , ICAM1 , and IL6mRNA expression, and upregulated CCND1 mRNA expression but had no
impact on MMP2 mRNA expression in the high-dose group (40
mg/kg/d) (Figure S8b). In summary, our data demonstrated that TA
substantially suppressed tumor growth via inhibiting STAT3 signaling
pathway in vivo .