| Primary liver cancer is the fifth most common cancer and the third leading causeof cancer death globally, including hepatocellular carcinoma, cholangiocarcinoma andhepatocholangiocarcinoma, among which hepatocellular carcinoma accounts for themajority. The leading cause of liver cancer is chronic active hepatitis, which includesviral hepatitis from HBV or HCV infection, alcoholic hepatitis and non-alcoholicfatty liver disease. Furthermore, HBV-induced chronic viral hepatitis is attributed tobe one of the main factors of the occurrence of hepatocellular carcinoma of Chinesepeople. Persistent liver cell death, infiltration of inflammatory cells and compensatoryhyperplasia of the liver is generally considered to be the pathological process ofinflammation-promoted hepatocarcinogenesis. Understanding the signaling pathwaysdriving or mediating these processes during hepatotumorigenesis is important fordeveloping novel treatments for this dreadful disease. A large number of studies basedon animal models show that TGF-β signliang pathway is playing an important role inregulating chronic inflammation-mediated hepatocarcinogenesis. However, mostresults didn’t display the consistent conclusion along with misunderstanding anduncertainty. Herein, based on analysis of a large number of human chronic hepatitisand HCC samples and some online data, combined with in vitro experiments and invivo animal models, the role of TGF-β signaling pathway in inflammation-promotedhepatocarcinogenesis have been systematically investigated, and the following mainresults are obtained:1. Based on analysis of TGF-β signaling associated protein expression in a largenumber of human liver cancer samples and some microarray data online, TGF-βsignaling was generally downregulated in HCC and TβRI/II mRNA expressionsignificantly was reduced as well as the downstream gene expression was inactivated. In addition, TβRII expression level increased along with the progression ofhepatocellular carcinoma.2. By measuring status of TGF-β signaling in HCC cell lines （SNU398，SNU423，HepG2，Sk-Hep-1and Huh7cells）, Sk-Hep-1and Huh7cells have intact TGF-βsignaling compared with HepG2cells known to own this signaling. This signaling inSNU423cells was wakened while SNU398has injuried TGF-β signaling withdeletion of the receptor II. However, it should be pointed out that all these cancer celllines can secrete different levels of TGF-β and exogenous TGF-β could inhibit growthof HCC cells that have intact TGF-β signaling pathway.3. Based on those above results, in order to weigh the effect of TGF-β signalingwithin these HCC cells themselves, the expression of TβRII, the main receptor inTGF-β signaling, were knockdown by lentiviral mediated shRNA in SNU423andSk-Hep-1. Apparent growth retardant and enhanced apoptosis was found due toTβRII knockdown. Tumor growth were significantly suppressed using subcutaneoustumor model injected with TβRII knockdown Sk-Hep-1, suppression effect on lungmetastasis was also obvious when TβRII was blocked.4. In order to further examine the respective effect of Smad and non-Smad in HCCcell lines, Smad4, the main receptor in TGF-β signaling, were knockdown bylentiviral mediated shRNA in Huh7and Sk-Hep-1. The similar results were obtainedthat apparent growth retardant and enhanced apoptosis was found as TβRIIknockdown. Meanwhile, the effect of TGF-β-mediated cell cycle arrest on HCC cellswas also attenuated in Smad4knockdown HCC cells.5. Downregulation of TGF-β signaling in SNU423, Sk-Hep-1and Huh7by usingshRNA targeting both TβRII and Smad4promoted cell apoptosis. Mechanism studyshows that knockdown of both TβRII and Smad4apparently inhibited expression ofphosphorylation of Smad3at Linker region in nucleus which could prevent from cellapoptosis; in addition, targeting Smad4also promoted expression of cancersuppressor gene PTEN and dephosphorylation of AKT, demonstrating the mechanismunderlying the inhibitory effect of attenuation of TGF-β signaling on HCC growthand metastasis. In conclusion, the pivotal roles of TGF-β signaling have been investigatedconcerning hepatic inflammation-induced carcinogenesis. On one hand, theinactivation of TGF-β signaling in liver cancer shields themselves from the inhibitoryeffect of this signaling on cell proliferation, impacting the progression of HCC; Onthe other hand, establishment of TGF-β in HCC cells favors the maintainance oftumor microenvironment, causing persistent activation and enhanced effect of thiscell signaling by sustained and enhanced secretion of cytokines, chemokines andgrowth factors. Clarification of the mechanism of chronic hepatitis-inducedhepatocarcinogenesis is important for the identification of novel therapeutic targets inHCC prevention and treatment. |
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