My group is currently focusing on investigating the mechanism that is involved in TGF-β production in human colon carcinoma cells. TGF-β suppresses cell growth in epithelial cells. However, in malignant cells, TGF-β often exhibits transforming effects, especially once the cells have lost negative growth control signals imparted by TGF-β Cancer cells can secret large quantities of TGFβ inducing a pro-oncogenic effect through stimulation of epithelial-to-mesenchymal transdifferentiation (EMT) and/or paracrine mechanisms. Strategies for cancer treatment could include interfering with TGFβ secretion as a means of reducing both the autocrine and/or paracrine pro-oncogenic effector functions of TGFβ in the tumor microenvironment. TGFβ production by tumor cells could possibly be inhibited by the use of small molecule inhibitors targeting the signal transduction pathways that mediate TGFβ expression in tumor cells. Such a strategy could be of great value and offer better drug specificity. However, the design of such small molecule inhibitors requires a greater understanding of the intracellular signaling pathways mediating TGFβ production by cancer cells. The research activity of our group is addressing this issue for human colon carcinoma cells. Our specific aims are to:

1. Define the most appropriate targets, either signaling components or transcription factors, for blocking TGFβ production.
2. Block these biological targets using siRNA approaches to determine whether the specific targets are required for TGFβ production by the tumor cells.
3. Determine whether tumor growth is suppressed both in vitro and in vivo when TGFβ production is blocked.
4. Design the most plausible and effective approach to inhibit the target element that is critical in mediating TGFβ production. Possible choices include devising small interfering RNA (siRNA), designing small molecule inhibitors, or constructing cell-penetrating and protease-resistant peptides to selectively bind and block the active site of the target element. In our recent progress, we have defined the critical motif and the transcription factor in the TGFβ1 promoter region. We have determined that the proximal AP-1 binding motif (-362 to ?355) is critical for mediating TGFβ1 expression. We have also identified that pro-oncogene protein c-Fos is the critical component in the AP-1 complex that is necessary for TGFβ1 gene expression in human colon carcinoma cells. Further, we have determined that blocking c-Fos by siRNA led to suppression of TGFβ1 gene expression, TGFβ1 production, and the subsequent cell migratory capacity of the cells.

In our other relevant projects, we have determined that the CRE binding motif in TGFβ3 promoter region is critical to TGFβ3 expression and that Smad3, but not Smad4, is involved in the CRE binding complex in response to TGFβ stimulation. We are also investigating a novel TGFβ receptor-interacting protein, termed km23, to identify how the protein is involved in TGFβ signaling pathways. Our major objective is to identify alterations in TGF-β signaling pathways that contribute to tumor formation or progression in colon cancer models. It is anticipated that specific TGF-β signaling components will prove to be critical therapeutic targets in the restoration of negative growth control by TGF-β to epithelial cancers. In addition, we hope to define which TGF-β signaling pathways lead to growth inhibitory effects in epithelial cells and which lead to cellular responses more often associated with the tumor-enhancing effects of TGF-β Selective stimulation or inhibition of these signaling pathways will be evaluated to determine their effects on tumor formation or progression in vivo.