Snorri S. Thorgeirsson

Acceleration of c-myc-Induced Hepatocarcinogenesis by Co-Expression of Transforming Growth Factor (TGF)-α in Transgenic Mice Is Associated with TGF-β1 Signaling Disruption

We have previously shown in transgenic mice that transforming growth factor (TGF)-alpha dramatically enhances c-myc-induced hepatocarcinogenesis by promoting proliferation and survival of hepatocellular carcinoma (HCC) cells. As transgenic livers display increased levels of mature TGF-beta1 from the early stages of hepatocarcinogenesis, we have now assessed whether impairment of TGF-beta1 signaling contributes to the deregulation of cell cycle progression and apoptosis observed during this process. Focal preneoplastic lesions lacking expression of TGF-beta receptor type II (TbetaRII) were detected in c-myc/TGF-alpha but not in c-myc livers. In c-myc/TGF-alpha mice, 40% (2/5) of adenomas and 90% (27/30) of HCCs showed down-regulation of TbetaRII expression in comparison with 11% (2/18) of adenomas and 47% (14/30) of HCCs in c-myc mice. Down-regulation of the TGF-beta1-inducible p15(INK4B) mRNA and reduced apoptotic rates in TbetaRII-negative HCCs further indicated the disruption of TGF-beta1 signaling. Furthermore, both TbetaRII-negative and -positive c-myc TGF-alpha HCCs, but not c-myc HCCs, were characterized by decreased levels of the cell cycle inhibitor p27. These results suggest 1) an inverse correlation of decreased p27 expression with the particularly strong expression of TGF-alpha in these lesions, consistent with the capacity of TGF-alpha signaling to post-transcriptionally regulate p27, and 2) the presence of alternative, downstream defects of TGF-beta1 signaling in c-myc/TGF-alpha HCCs that may impair the growth-inhibitory response to TGF-beta1. Thus, the accelerated neoplastic development in c-myc/TGF-alpha mice is associated with an early and frequent occurrence of TbetaRII-negative lesions and with reduced levels of p27 in HCC cells, indicating that disruption of TGF-beta1 responsiveness may play a crucial role in the enhancement of c-myc-induced hepatocarcinogenesis by TGF-alpha.

Molecular genetics of liver neoplasia

Primary liver cancer (PLC) is the third most deadly and fifth most common cancer in the world (Parkin et al. 1999), with an estimated 626,000 or 5.7% of new cancer cases and almost as many deaths in 2002 (Parkin et al. 2005). Liver cancer is an ancient disease and its description can be found in Huangdi Neijing, an ancient Chinese medical textbook also known as Yellow Emperor’s Inner Canon dated back over 2000 years ago. However, the first mentioned PLC case could be dated as early as 1849 by Carl Rokitansky and the definition of PLC, as referenced to metastatic liver cancer, was only formally established in 1888 by Victor Hanot and Augustin Gilbert, and in 1889 independently by Moriharu Miura (Hanot and Gilbert 1888; Rokitansky 1849; Yamagiwa 1911). Traditionally, PLC was considered as an incurable disease due to an extremely poor outcome. Patients with PLC have been an underserved population since the beginning of its discovery and the disease is becoming a major health burden worldwide. Clearly, there is a strong need in expanding basic and translational research on PLC with an ultimate goal to reduce its severity. Recent studies on HCC genetic and genomic analyses feature important advances in the understanding of the complex biological processes underlying tumorigenesis and metastasis of PLC, and demonstrate how these insights might translate into clinical applications. As we approach a golden era in PLC research, we anticipate a significant advance in our understanding of this disease in near future. We are confident that the knowledge gain from continuing research efforts on PLC undoubtedly facilitates the understanding of molecular mechanism and tumor biology to provide the best therapy for each cancer patient and to improve patient management. X.W. Wang (B) Liver Carcinogenesis Section, Laboratory of Human Carcinogenesis, National Cancer Institute, NIH, 37 Convent Drive, MSC 4258, Building 37, Room 3044A, Bethesda, MD 20892, USA e-mail: xw3u@nih.gov 3 X.W. Wang et al. (eds.), Molecular Genetics of Liver Neoplasia, Cancer Genetics, DOI 10.1007/978-1-4419-6082-5_1, C

45 – Early Activation and Expansion of Hepatic Stem Cells

This chapter reviews the cellular and molecular biology of hepatocyte lineage generation from stem cells, particularly, the early steps of activation and expansion. Hepatic parenchymal cells (hepatocytes and cholangiocytes) in adult animals are mitotically quiescent under physiological conditions. Both types of cells live long in the absence of trauma or toxicity. However, the liver is frequently exposed to both physical trauma and potent hepatotoxins, and unexpected loss of hepatocytes and cholangiocytes is not uncommon. Perhaps, because of this situation, and because the maintenance of liver function is necessary to preserve the life of the organism, several cellular mechanisms have evolved to replace hepatocytes. Unlike the parenchymal cells of most adult tissues, the hepatocytes and cholangiocytes that remain after cell loss are able to proliferate quickly to generate additional copies to replace a deficit or even to increase hepatic function in the absence of cell loss. Additionally, when the residual parenchymal cells cannot proliferate after cell loss, new lineages of hepatocytes and cholangiocytes can be generated from stem cells.

Cancer Stem Cells and Liver Cancer

The cancer stem-cell hypothesis proposes that tumors contain a distinct subpopulation of cells which are exclusively responsible for the initiation and maintenance of the cancer. These cells are referred to as either tumor-initiating cells or cancer stem cells (CSC). CSC were first identified in hematologic malignancies, but there is increasing evidence that variety of solid tumors (e.g., in breast, brain, pancreas, colon, and liver) are hierarchically organized and sustained by a distinct subpopulation of CSC. The frequency of CSC in solid tumors is variable indicating both biological variation and technical issues. The existence of CSC also poses a significant clinical challenge since CSC have been shown to be more resistant to chemotherapy and radiotherapy. Consequently, identification and prospective characterization of the CSC in liver cancer promises to have an enormous impact on the development of both, novel diagnostic and therapeutic approaches. This chapter will include a background on the general concept of CSC; a presentation of different isolation methods for CSC; a discussion on the putative origin of the CSC; and a critical discussion of selected recent publications dealing with the existence, identification, and elimination of human liver CSC.

Biology of Hepatocellular Carcinoma: Past, Present and Beyond

Primary liver cancer (PLC) is the third most deadly and fifth most common cancer in the world (Parkin et al. 1999), with an estimated 626,000 or 5.7% of new cancer cases and almost as many deaths in 2002 (Parkin et al. 2005). Liver cancer is an ancient disease and its description can be found in Huangdi Neijing, an ancient Chinese medical textbook also known as Yellow Emperor’s Inner Canon dated back over 2000 years ago. However, the first mentioned PLC case could be dated as early as 1849 by Carl Rokitansky and the definition of PLC, as referenced to metastatic liver cancer, was only formally established in 1888 by Victor Hanot and Augustin Gilbert, and in 1889 independently by Moriharu Miura (Hanot and Gilbert 1888; Rokitansky 1849; Yamagiwa 1911). Traditionally, PLC was considered as an incurable disease due to an extremely poor outcome. Patients with PLC have been an underserved population since the beginning of its discovery and the disease is becoming a major health burden worldwide. Clearly, there is a strong need in expanding basic and translational research on PLC with an ultimate goal to reduce its severity. Recent studies on HCC genetic and genomic analyses feature important advances in the understanding of the complex biological processes underlying tumorigenesis and metastasis of PLC, and demonstrate how these insights might translate into clinical applications. As we approach a golden era in PLC research, we anticipate a significant advance in our understanding of this disease in near future. We are confident that the knowledge gain from continuing research efforts on PLC undoubtedly facilitates the understanding of molecular mechanism and tumor biology to provide the best therapy for each cancer patient and to improve patient management.

Overview of Cholangiocarcinoma and Evidence for a Primary Liver Carcinoma Spectrum

Intrahepatic cholangiocarcinoma, second in incidence to hepatocellular carcinoma among the primary liver carcinomas, has an even more dismal prognosis. Intrahepatic cholangiocarcinoma is difficult to diagnose at an early stage of development and advances aggressively, with widespread metastases. Molecular genetic features of intrahepatic cholangiocarcinoma have been partially elucidated, although the specific genetic lesions and molecular processes that drive its development, progression, and metastasis are still obscure. Evidence has accumulated from many sources suggesting that cholangiocarcinoma and hepatocellular carcinoma are components of a spectrum of primary liver carcinomas, including poorly and aberrantly differentiated varieties. Primary liver carcinomas arise from cells in different stages of development that encompass the entire lineage of liver epithelial cells generated from hepatoblasts and/or adult liver stem cells, and share critical genomic aberrations and phenotypes with these progenitor cells.

Transgenic and Knockout Mouse Models of Liver Cancer

Hepatocellular carcinoma (HCC) is one of the most frequent and deadliest tumors worldwide. Only few patients are amenable to surgery due to the late HCC diagnosis, and alternative treatments do not significantly improve the patient prognosis when tumor is unresectable. Thus, the investigation of HCC biology is required to identify new targets for early diagnosis, chemoprevention, and treatment. To study the molecular events leading to liver malignant transformation and tumor progression, a number of mouse models have been generated. Here, we highlight some of the genetically engineered mouse models that have proved to be valuable tools to study the molecular pathogenesis of human liver cancer. Also, we briefly describe the similarities between human and mouse HCC at the molecular level with emphasis on the advantages and disadvantages of each model. Although additional work is required, the data show that engineered mouse models have provided a significant contribution in our understanding of the pathogenesis of HCC. In particular, the mouse models have allowed the step-by-step analysis of the multiple stages of liver carcinogenesis with the identification of the underlying alterations in signal transduction pathways, cell cycle, and epigenetic and genetic mechanisms involved. Furthermore, the information obtained from these mouse models will help to design new, more specific and effective therapeutic approaches against human HCC.