The role of transforming growth factor-beta in suppression of hepatic metastasis from colon cancer

BMI-1 activates hepatic stellate cells to promote the epithelial-mesenchymal transition of colorectal cancer cells

BACKGROUND

Activated hepatic stellate cells (aHSCs) are the major source of cancer-associated fibroblasts in the liver. Although the crosstalk between aHSCs and colorectal cancer (CRC) cells supports liver metastasis (LM), the mechanisms are largely unknown.

AIM

To explore the role of BMI-1, a polycomb group protein family member, which is highly expressed in LM, and the interaction between aHSCs and CRC cells in promoting CRC liver metastasis (CRLM).

METHODS

Immunohistochemistry was carried out to examine BMI-1 expression in LM and matched liver specimens of CRC. The expression levels of BMI-1 in mouse liver during CRLM (0, 7, 14, 21, and 28 d) were detected by Western blotting (WB) and the quantitative polymerase chain reaction (qPCR) assay. We overexpressed BMI-1 in HSCs (LX2) by lentivirus infection and tested the molecular markers of aHSCs by WB, qPCR, and the immunofluorescence assay. CRC cells (HCT116 and DLD1) were cultured in HSC-conditioned medium (LX2 NC CM or LX2 BMI-1 CM). CM-induced CRC cell proliferation, migration, epithelial-mesenchymal transition (EMT) phenotype, and transforming growth factor beta (TGF-β)/SMAD pathway changes were investigated in vitro. A mouse subcutaneous xenotransplantation tumor model was established by co-implantation of HSCs (LX2 NC or LX2 BMI-1) and CRC cells to investigate the effects of HSCs on tumor growth and the EMT phenotype in vivo.

RESULTS

Positive of BMI-1 expression in the liver of CRLM patients was 77.8%. The expression level of BMI-1 continued to increase during CRLM in mouse liver cells. LX2 overexpressed BMI-1 was activated, accompanied by increased expression level of alpha smooth muscle actin, fibronectin, TGF-β1, matrix metalloproteinases, and interleukin 6. CRC cells cultured in BMI-1 CM exhibited enhanced proliferation and migration ability, EMT phenotype and activation of the TGF-β/SMAD pathway. In addition, the TGF-βR inhibitor SB-505124 diminished the effect of BMI-1 CM on SMAD2/3 phosphorylation in CRC cells. Furthermore, BMI-1 overexpressed LX2 HSCs promoted tumor growth and the EMT phenotype in vivo.

CONCLUSION

High expression of BMI-1 in liver cells is associated with CRLM progression. BMI-1 activates HSCs to secrete factors to form a prometastatic environment in the liver, and aHSCs promote proliferation, migration, and the EMT in CRC cells partially through the TGF-β/SMAD pathway.

TGF-β signaling in liver metastasis

The presence of liver metastases drastically worsens the prognosis of cancer patients. The liver is the second most prevalent metastatic site in cancer patients, but systemic therapeutic opportunities that target liver metastases are still limited. To aid the discovery of novel treatment options for metastatic liver disease, we provide insight into the cellular and molecular steps required for liver colonization. For successful colonization in the liver, adaptation of tumor cells and surrounding stroma is essential. This includes the formation of a pre-metastatic niche, the creation of a fibrotic and immune suppressive environment, angiogenesis, and adaptation of tumor cells. We illustrate that transforming growth factor β (TGF-β) is a central cytokine in all these processes. At last, we devise that future research should focus on TGF-β inhibitory strategies, especially in combination with immunotherapy. This promising systemic treatment strategy has potential to eliminate distant metastases as the efficacy of immunotherapy will be enhanced.

Weighted gene co-expression network analysis of colorectal cancer liver metastasis genome sequencing data and screening of anti-metastasis drugs

Approximately 9% of cancer-related deaths are caused by colorectal cancer (CRC). CRC patients are prone to liver metastasis, which is the most important cause for the high CRC mortality rate. Understanding the molecular mechanism of CRC liver metastasis could help us to find novel targets for the effective treatment of this deadly disease. Using weighted gene co-expression network analysis on the sequencing data of CRC with and with metastasis, we identified 5 colorectal cancer liver metastasis related modules which were labeled as brown, blue, grey, yellow and turquoise. In the brown module, which represents the metastatic tumor in the liver, gene ontology (GO) analysis revealed functions including the G-protein coupled receptor protein signaling pathway, epithelial cell differentiation and cell surface receptor linked signal transduction. In the blue module, which represents the primary CRC that has metastasized, GO analysis showed that the genes were mainly enriched in GO terms including G-protein coupled receptor protein signaling pathway, cell surface receptor linked signal transduction, and negative regulation of cell differentiation. In the yellow and turquoise modules, which represent the primary non-metastatic CRC, 13 downregulated CRC liver metastasis-related candidate miRNAs were identified (e.g. hsa-miR-204, hsa-miR-455, etc.). Furthermore, analyzing the DrugBank database and mining the literature identified 25 and 12 candidate drugs that could potentially block the metastatic processes of the primary tumor and inhibit the progression of metastatic tumors in the liver, respectively. Data generated from this study not only furthers our understanding of the genetic alterations that drive the metastatic process, but also guides the development of molecular-targeted therapy of colorectal cancer liver metastasis.

Long term effect of curcumin in restoration of tumour suppressor p53 and phase-II antioxidant enzymes via activation of Nrf2 signalling and modulation of inflammation in prevention of cancer

Inhibition of carcinogenesis may be a consequence of attenuation of oxidative stress via activation of antioxidant defence system, restoration and stabilization of tumour suppressor proteins along with modulation of inflammatory mediators. Previously we have delineated significant role of curcumin during its long term effect in regulation of glycolytic pathway and angiogenesis, which in turn results in prevention of cancer via modulation of stress activated genes. Present study was designed to investigate long term effect of curcumin in regulation of Nrf2 mediated phase-II antioxidant enzymes, tumour suppressor p53 and inflammation under oxidative tumour microenvironment in liver of T-cell lymphoma bearing mice. Inhibition of Nrf2 signalling observed during lymphoma progression, resulted in down regulation of phase II antioxidant enzymes, p53 as well as activation of inflammatory signals. Curcumin potentiated significant increase in Nrf2 activation. It restored activity of phase-II antioxidant enzymes like GST, GR, NQO1, and tumour suppressor p53 level. In addition, curcumin modulated inflammation via upregulation of TGF-β and reciprocal regulation of iNOS and COX2. The study suggests that during long term effect, curcumin leads to prevention of cancer by inducing phase-II antioxidant enzymes via activation of Nrf2 signalling, restoration of tumour suppressor p53 and modulation of inflammatory mediators like iNOS and COX2 in liver of lymphoma bearing mice.