Transforming growth factor-β1 (TGF-β1) induces stromal fibroblast-to-myofibroblast transdifferentiation in the tumor-stroma interactive microenvironment via modulation of multiple phenotypic and functional genes, which plays a critical role in tumor progression.
This process includes the induction of Smad2/3 phosphorylation, the increase of Smad2/3 transcriptional activity and the upregulation of the expression of target genes involved in EMT and cancer progression (such as TGF-β1, MMP-2, MMP-9, plasminogen activator inhibitor type-1, vascular endothelial growth factor, Snail and Slug), thus promoting cancer cell mobility and invasion.
Identification of Hdm2 as a downstream target of TGF-beta1 represents a critical prosurvival mechanism in cancer progression and provides another point for therapeutic intervention in late-stage cancer.
Moreover, there is growing evidence that TGF-beta1 contributes to tumor progression by regulating tumor cell proliferation and differentiation, inducing a favorable tumor microenvironment, promoting migration and invasion, and suppressing macrophage cytotoxicity.
In addition, the up-regulation of BIGH3 and PAI-1 was found to correlate with the clinicopathological parameters associated with a poorer patient outcome, whereas TGF-beta1 expression was determined to be unrelated to cancer progression.
This suggests that genotypes provisionally associated with low expression of pro-inflammatory and immunomodulatory TNF-alpha, IFN-gamma and IL-6 and anti-inflammatory IL-10 and TGF-beta1 could be involved in the mechanisms of cancer progression and escape from immunosurveillance.
Transforming growth factor beta 1 (TGF-beta1) is a potent tumor suppressor but, paradoxically, TGF-beta1 enhances tumor growth and metastasis in the late stages of cancer progression.
In the present study, SD-208, a 2,4-disubstituted pteridine, ATP-competitive inhibitor of the TGFbeta receptor I kinase (TGFbetaRI), was used to inhibit cellular activities and tumor progression of PANC-1, a human pancreatic tumor line.
We found that in pancreatic cancer cells Smad proteins and Sp1 cooperatively regulate expression of a distinct set of TGFbeta target genes potentially involved in tumor progression, including MMP-11, cyclin D1 and Smad7.
Animal experiments suggest that TGF-beta1 plays a biphasic role in carcinogenesis by protecting against the early formation of benign epithelial growths, but promoting a significant stimulation of tumor growth invasion and metastasis during tumor progression.
Since decreased expression of ICAM-1 has been known to contribute to cancer cell escape from immunologic recognition and cytotoxicity by effector cells, the present results indicate that unknown function of TGF-beta1 in the tumor progression and metastasis of pancreatic cancer.
The constant low concentration of TGF-beta1 in the tumour mass may be related to the low content of antiproliferative HNE observed in colon cancer: the latter phenomenon, which reduces TGF-beta1 production in the tumour area, may represent a favourable condition for neoplastic progression.