Establishment and characterization of a nontumorigenic cell line derived from a human hepatocellular adenoma expressing hepatocyte-specific markers

Nuclear accumulation of seven in absentia homologue-2 supports motility and proliferation of liver cancer cells

Stability of many tumor-relevant proteins is partly mediated by E3 ligases, which determine substrate specificity within the ubiquitin system. Recent data demonstrated that increased nuclear expression of the E3 ligase seven in absentia homologue (SIAH)-1 in human hepatocarcinogenesis supports tumor cell proliferation and migration. To define whether closely related SIAH-2 synergizes with protumorigenic SIAH-1, we systematically analyzed expression, localization and functional relevance of SIAH-2 in human hepatocellular carcinoma (HCC). Nuclear accumulation of SIAH-2 is detectable in more than 60% of all HCCs and correlates with tumor progression, cell proliferation and distant metastasis. An inverse correlation between nuclear SIAH-1 and SIAH-2 was detected, suggesting independent mechanisms for nuclear enrichment. Inhibition of nuclear SIAH-2 by RNAi in HCC cell lines reduced proliferation as well as lateral tumor cell motility and transmigration; however, combined knock down of both SIAH-1 and SIAH-2 did not further amplify biological effects compared to single gene inhibition. Reduction of SIAH-2 expression sensitizes HCC cells to the treatment with different cytostatic drugs, demonstrating that SIAH-2-targeting approaches may increase the response of HCC cells to conventional chemotherapy. Together, these data show that SIAH-2--as described for SIAH-1--accumulates in nuclei of HCC cells where it supports tumor growth and tumor cell dissemination. Because the nuclear pattern of SIAH-2 differs in HCC tissues from the SIAH-1 pattern and because the inactivation of SIAH-2 is not compensated by SIAH-1, the specific inhibition of SIAH-2 (especially in combination with other drugs) represents a promising therapeutic strategy for HCC.

Targeting heat shock protein 90 with non-quinone inhibitors: a novel chemotherapeutic approach in human hepatocellular carcinoma

The inhibition of heat shock protein 90 (Hsp90) has emerged as a promising antineoplastic strategy in diverse human malignancies. Hsp90 has been predicted to be involved in hepatocellular carcinoma (HCC) development; however, its role in hepatocarcinogenesis remains elusive. Using chemically distinctive Hsp90 inhibitors, we show that Hsp90 capacitates the aberrant expression and activity of crucial hepatocarcinogenesis-driving factors (e.g., insulin-like growth factor receptor 1, hepatocyte growth factor receptor, protein kinase B, v-raf-1 murine leukemia viral oncogene homolog 1, and cyclin-dependent kinase 4). In vitro, Hsp90 inhibition with both geldanamycin analogs (17-allylamino-17-desmethoxygeldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-desmethoxygeldanamycin (17-DMAG)) and the non-quinone compound 8-(6-iodobenzo[d][1,3]dioxol-5-ylthio)-9-(3-(isopropylamino)propyl)-9H-purin-6-amine (PU-H71) reduced the viability of various HCC cell lines, induced the simultaneous degradation of numerous hepatocarcinogenic factors, and caused substantial cell cycle arrest and apoptosis. In contrast, nontumorigenic hepatocytes were less susceptible to Hsp90 inhibition. Because conventional geldanamycin-derivate Hsp90 inhibitors induce dose-limiting liver toxicity, we tested whether novel Hsp90 inhibitors lacking the benzoquinone moiety, which has been deemed responsible for hepatotoxicity, can elicit antineoplastic activity without causing significant liver damage. In HCC xenograft mouse models, PU-H71 was retained in tumors at pharmacologically relevant concentrations while being rapidly cleared from nontumorous liver. PU-H71 showed potent and prolonged in vivo Hsp90 inhibitory activity and reduced tumor growth without causing toxicity.

CONCLUSION

Hsp90 constitutes a promising therapeutic target in HCC. Non-quinone Hsp90 inhibitors exhibit tumor-specific accumulation and exert potent antineoplastic activity without causing significant hepatotoxicity.

Autocrine/paracrine secreted Frizzled-related protein 2 induces cellular resistance to apoptosis: a possible mechanism of mammary tumorigenesis

Abnormal regulation of apoptosis and cell proliferation is thought to be involved in tumor formation. The secreted Frizzled-related protein 2 (SFRP2) was detected in primary culture of canine mammary gland tumors but not in normal mammary tissues. Thus, to elucidate the role of SFRP2 in mammary tumorigenesis, we overexpressed SFRP2 in mammary gland tumor and MCF7 cells. The results indicated that SFRP2 is secreted and incorporated into the extracellular matrix (ECM) of the tumor and normal cells. In an attempt to understand the molecular basis underlying the interaction between SFRP2 and ECM, co-immunoprecipitation and cell adhesion assays were carried out. SFRP2 was found to be associated with the fibronectin-integrin protein complex and could promote cell adhesion. DNA fragmentation and caspase 3 activity analyses showed that the susceptibility of the cells to UV-induced apoptosis decreased in the context of SFRP2 overexpression. Upon disruption of the fibronectin-integrin connection, the antiapoptosis activity of SFRP2 was decreased. Moreover, SFRP2 was found to induce tumorous transformation in normal mammary epithelial cells and to inhibit apoptosis in a modified paracrine model. Collectively, our results emphasize the relevance of SFRP2 and ECM in mammary tumorigenesis and provide further insight into the mechanism of SFRP2 action.

Expression of secreted frizzled-related protein 2 in a primary canine mammary tumor cell line: a candidate tumor marker for mammary tumor cells

Canine mammary tumors (CMTs) have been proposed to be a good animal model for human breast cancer. To provide a basis for the tumorigenic study of CMTs, cell lines were established using a modified cell culture technique. The epithelial morphology and immunostaining with cytokeratin 18 confirmed the epithelial origin of the cells. In an investigation of possible mammary tumorigenesis-related factors, the expression of Wnt signaling-related proteins was detected in cell lines. Secreted frizzled-related protein 2 (SFRP2) was abundantly expressed in CMT cells but not in normal canine mammary gland (MG) cells. Secreted frizzled-related protein 2 was secreted into the culture medium and was associated with the extracellular matrix. In addition, increased expressions of beta-catenin and cyclin D1 were observed in cells overexpressing SFRP2. The marked differential expression of SFRP2 reveals that this protein may be a potential candidate marker for CMTs. The CMT cell line established in this study provides a useful tool and experimental model for understanding both the tumorigenesis of CMTs and the role of Wnt signaling in cancers.

P53 gene and Wnt signaling in benign neoplasms: beta-catenin mutations in hepatic adenoma but not in focal nodular hyperplasia

Hepatocellular adenoma (HA) and focal nodular hyperplasia (FNH) are 2 rare, benign liver neoplasms that often are discovered incidentally. To date, few genetic changes have been found in these 2 benign lesions. However, the 2 pathways of p53 and Wnt signaling, which may be the most common molecular targets involved in liver tumorgenesis, were studied in HA and FNH. Ten HAs and 11 FNHs were analyzed for loss of heterozygosity (LOH) and sequencing analysis of mutation hot spots in exons 5 to 8 of the p53 gene. No LOH or mutant sequences were identified, indicating that p53 was not associated with these benign lesions. Genes in the Wnt signaling pathway, including beta-catenin, axin, and adenomatous polyposis coli (APC), also were studied. Polymerase chain reaction (PCR) amplification and direct sequencing of all samples of HA and FNH displayed no mutations in exon 3 of the beta-catenin gene. However, 3 HAs (30%) contained interstitial deletions from exon 3 to exon 4. Truncated forms of beta-catenin detected by Western blot and immunohistochemical analyses showed they had accumulated in the cytoplasm and nuclei. However, for the axin and APC genes, no genetic changes, including allelic loss, interstitial deletions and point mutations, were detected in any of the HAs and FNHs. In conclusion, beta-catenin, which participates in the Wnt signaling pathway, might play a more important role in the formation of HA than in that of FNH, but p53 is not associated with the development of either HA or FNH.

Chromosomal analysis of hepatic adenoma and focal nodular hyperplasia by comparative genomic hybridization

Hepatic adenoma (HA) and focal nodular hyperplasia (FNH) are two common non-malignant tumors of the liver. Genomic analysis on these benign lesions may shed light on the genetic mechanism underlying liver carcinogenesis. We used comparative genomic hybridization (CGH) to evaluate genomic changes in eight cases of HA and six cases of FNH, obtained by surgical procedures; the resulting chromosomal aberration profiles were analyzed together with their pathological and clinical manifestations. We found consistent chromosomal lesions associated with both non-malignant hepatic tumors. The overall genomic abnormalities in HA and FNH were much less obvious than those in hepatocellular carcinoma (HCC). Among these limited changes, frequent gains were located on chromosomal arms 1q (50%), 17q (50%), 1p (38%), and 11q (38%) in HA, and on 11q (50%), 9q (33%), 17q (33%), and 22q (33%) in FNH. Gains outnumbered losses, and HA contained more CGH abnormalities than did FNH. Interestingly, CGH alteration hotspots found in HA, but not in FNH, appeared largely to coincide with common genomic lesions of cancerous HCC, suggesting an interesting relationship along the tumorigenesis pathway of HA and HCC.

Cell line provenance

Cultured cell lines have become an extremely valuable resource, both in academic research and in industrial biotechnology. However, their value is frequently compromised by misidentification and undetected microbial contamination. As detailed elsewhere in this volume, the technology, both simple and sophisticated, is available to remedy the problems of misidentification and contamination, given the will to apply it. Combined with proper records of the origin and history of the cell line, assays for authentication and contamination contribute to the provenance of the cell line. Detailed records should start from the initiation or receipt of the cell line, and should incorporate data on the donor as well as the tissue from which the cell line was derived, should continue with details of maintenance, and include any accidental as well as deliberate deviations from normal maintenance. Records should also contain details of authentication and regular checks for contamination. With this information, preferably stored in a database, and suitable backed up, the provenance of the cell line so created makes the cell line a much more valuable resource, fit for validation in industrial applications and more likely to provide reproducible experimental results when disseminated for research in other laboratories.

Hepatic progenitor cells in hepatocellular adenomas

Hepatocellular adenoma is a benign tumor of the liver that has a small but not negligible risk of malignant transformation into hepatocellular carcinoma. In analogy with the established role of oval cells in hepatocarcinogenesis in rodent models, human hepatic progenitor cells may have a function in the development of liver tumors. To investigate this issue, we performed immunohistochemistry on biopsies of 10 consecutively resected hepatocellular adenomas using markers for hepatic progenitor cells. Sections of paraffin-embedded and frozen biopsies were stained using antibodies against cytokeratins 7, 8, 18, and 19, chromogranin-A, OV-6, and neural cell adhesion molecule. Hepatic progenitor cells were observed in five of 10 hepatocellular adenomas. These five tumors also contained cells with an immunohistochemical phenotype intermediate between hepatic progenitor cells and hepatocytes. Hepatic progenitor cells and intermediate hepatocyte-like cells were scattered throughout the tumors with a density that varied from area to area. Ultrastructural examination confirmed the presence of hepatic progenitor cells. Our study shows that hepatic progenitor cells are present in a considerable proportion of hepatocellular adenomas, supporting the hypothesis that human hepatic progenitor cells can play a role in the development of hepatocellular tumors.

The role of wild-type and mutated N-ras in the malignant transformation of liver cells

In order to determine the role of N-ras overexpression and mutation in malignant liver cell transformation, wild-type and mutated N-ras were transfected into the rat liver epithelial cell line OC/CDE 22, and N-ras expression, growth kinetics, growth in soft agar, and tumorigenicity in vivo as well as the involvement of the mitogen-activated protein kinase (MAPK) signal transduction pathway in the expression of the malignant phenotype were analyzed. Although OC/CDE 22 cells transfected with wild-type N-ras showed a high expression of N-ras at the mRNA and protein levels, the cells did not grow in soft agar and were not tumorigenic in vivo. In contrast, OC/CDE 22 cells transfected with mutated N-ras showed anchorage-independent growth and were tumorigenic. When cultured in fetal bovine serum-supplemented medium, OC/CDE 22 cells expressing mutant N-ras showed a higher proliferation rate than nontransfected OC/CDE 22 cells or OC/CDE 22 cells transfected with wild-type N-ras. When held in serum-free medium, untreated OC/CDE 22 cells did not grow at all, while OC/CDE 22 cells transfected with wild-type or mutant N-ras proliferated at a similar rate, which can be explained by the high MAPK activity in these cells. Selective inhibition of the MAPK cascade abolished the growth of OC/CDE 22 cells carrying mutant N-ras in soft agar; furthermore, these cells ceased pile up and formed monolayers on Petri dishes. Thus, activation of the MAPK signaling pathway, though alone not sufficient to malignantly transform liver cells (as shown in liver cells overexpressing wild-type N-ras), is not only essential for growth control but also for the expression of the malignant phenotype (as demonstrated in liver cells transformed by mutated N-ras).

The human p53 gene mutated at position 249 per se is not sufficient to immortalize human liver cells

A particular point mutation of the tumor suppressor gene p53, namely a G-->T transversion at the third base of codon 249, is frequently detected in primary hepatocellular carcinomas from patients living in areas where the levels of dietary exposure to aflatoxin B1 and the rates of infection with the hepatitis B virus are very high. Very recently, a nontumorigenic liver epithelial cell line (HACL-1) with a finite life-span and expressing a number of hepatocyte-specific markers was established from a human hepatocellular adenoma in our laboratory. To analyze the role of mutated p53 in the immortalization of human liver cells, we transfected HACL-1 cells with an expression vector containing a human p53 complementary DNA mutated at the third base of codon 249 and analyzed the consequences of this gene transfer on the growth properties of this cell line. HACL-1 cells transfected with mutant p53 showed no increase in their life-span (when compared with HACL-1 cells transfected with the antibiotic resistance gene alone) and did not grow in soft agar, whereas transfection of wild-type p53 into HACL-1 cells led to a proliferation stop. Thus, these results strongly support the view that the mutation at codon 249 of the p53 gene may serve as a fingerprint for aflatoxin B1-induced hepatocellular carcinomas, but is not, by itself, sufficient to immortalize human liver cells.