Heterogenic TGF-β response in HCC cell lines displays the divergent in vivo HCC phenotype

Hepatocellular carcinoma (HCC) is a heterogenic cancer type with symptoms occurring very late in disease progression. Due to this, it is still challenging to develop efficient therapies. Therefore, HCC represents one of the most common and deadliest cancers worldwide.

TGF-β is a driver of chronic liver disease progression, which eventually ends in HCC. TGF-β, a tumor suppressor in cancer development, exerts tumor promoting characteristics during cancer progression. Together with the strong heterogeneity of HCC this leads to a complex situation in regard of TGF-β signaling in liver tumorigenesis.

To identify possible roles of TGF-β signaling components in HCC, we investigated 10 different HCC cell lines: Real time PCR analysis showed that Smad7– an efficient inhibitor of canonical TGF-β signaling – expression is strongly varying in different cell lines. However, Smad7 expression levels were highly correlated (inversely) to the TGF-β dependent activation of the canonical Smad2 but not Smad3 pathway (Western blot, Smad3 reporter assay). Interestingly, the latter one was less active in cell lines insensitive to TGF-β induced cell death (7 cell lines). Further, we were able to show growth arrest in some cell lines upon TGF-β treatment (MTT assay). Other cell lines did not show any influence of TGF-β on cell growth while in one proliferation was even induced.

These findings probably reflect the different functions of TGF-β in HCC development and progression. Besides heterogeneity of the TGF-β response, we also identified varying autocrine TGF-β signaling levels. Further, cells with elevated Smad7 expression showed increased TGF-β mRNA levels. These findings suggest a mechanism to protect cells from tumor suppressing TGF-β effects, while in parallel profiting from tumor supporting features

In summary, we show a strongly heterogenic TGF-β response in 10 different HCC cell lines. As TGF-β signaling shows ambiguous functions in carcinogenesis, it is still hard to predict if or in which stage of hepatocarcinogenesis (aberrant) TGF-β signaling fulfills tumor promoting or suppressing tasks. Therefore, the cell lines with their varying TGF-β responses offer individual scenarios to analyze different mechanisms for a better understanding of diverse in vivo situations.