Hepatocellular carcinoma (HCC) is a prevalent cancer in sub-Saharan Africa and eastern Asia. Hepatitis B virus and aflatoxins are risk factors for HCC, but the molecular mechanism of human hepatocellular carcinogenesis is largely unknown. Abnormalities in the structure and expression of the tumour-suppressor gene p53 are frequent in HCC cell lines, and allelic losses from chromosome 17p have been found in HCCs from China and Japan. Here we report on allelic deletions from chromosome 17p and mutations of the p53 gene found in 50% of primary HCCs from southern Africa. Four of five mutations detected were G----T substitutions, with clustering at codon 249. This mutation specificity could reflect exposure to a specific carcinogen, one candidate being aflatoxin B1 (ref. 7), a food contaminant in Africa, which is both a mutagen that induces G to T substitution and a liver-specific carcinogen.

Mutations in the p53 gene have been associated with a wide range of human tumors, including osteosarcomas. Although it has been shown that wild-type p53 can block the ability of E1a and ras to cotransform primary rodent cells, it is poorly understood why inactivation of the p53 gene is important for tumor formation. We show that overexpression of the gene encoding wild-type p53 blocks the growth of osteosarcoma cells. The growth arrest was determined to be due to an inability of the transfected cells to progress into S phase. This suggests that the role of the p53 gene as an antioncogene may be in controlling the cell cycle in a fashion analogous to the check-point control genes in Saccharomyces cerevisiae.

There is little information regarding the molecular mechanisms of hepatocarcinogenesis. We studied the p53 gene at the DNA, RNA, and protein level in seven human hepatocellular carcinoma (HCC)-derived cell lines; six of seven showed p53 abnormalities. By Southern blotting, the p53 gene was found to be partially deleted in Hep 3B and rearranged in SK-HEP-1 cells. Mahlavu cells showed a slower migration on SDS/polyacrylamide gels suggesting it was an abnormal protein. In' Huh7 cells, p53 protein had a prolonged half-life leading to its accumulation in the nuclei; increased levels of p53 protein were also found by immunoblotting. The p53 gene and its expression appeared to be unaltered in the hepatoblastoma-derived Hep G2 cell line. We found that the loss of p53 expression did not occur as a late in vitro event in the FOCUS cell line because p53 protein was also nondetectable at an early passage. We conclude that the loss of p53 expression or the presence of abnormal forms of the protein are frequently associated with HCC cell line-. These observations suggest that alterations in p53 may be important events in the transformation of hepatocytes to the malignant phenotype.Human hepatocellular carcinoma (HCC) is one of the most frequent tumors worldwide. Although HCC is relatively rare in North America and Europe, it ranks as one ofthe four most prevalent malignant diseases of adults in China, Taiwan, Korea, and sub-Saharan Africa (1). Infection with hepatitis B virus (HBV) as well as alcoholic cirrhosis and other factors associated'with chronic inflammatory and hepatic regenerative changes are found to be important risk factors for hepatocarcinogenesis (1-3). However, the molecular mechanisms involved in malignant transformation of hepatocytes remain largely unknown'. Because of strong epidemiological evidence showing a close correlation between the prevalence of hepatitis B surface antigen chronic carriers and the incidence of HCC, the role of HBV in hepatocarcinogenesis has been extensively studied (4). However, the HBV genome is unlikely to carry oncogenic sequences, and there is little evidence to suggest that integration of viral DNA into hepatocyte DNA activates cellular protooncogenes (3). Indeed, no specific association between activation of any known oncogene and HCC has yet been found.The role of recessive oncogenes in HCC has not been studied in detail. T'ang et al. (5) Immunoblotting. Cell and tissue extracts were prepared as described (24) and samples adjusted to'equal protein concentrations (100-200 ,ug) were separated by SDS/PAGE, electrotransferred to nitrocellulose paper, and analyzed by using the 1251-labeled Pabl22 antibody (25).Indirect Immunofluorescence. Cells grown on cover slips under standard culture conditions were used for indirect immunostaining with monoclonal antibody (mAb) Pabl22 by using a described protocol with minor modifications (26). Briefly, cells were fixed in 4% (vol/vol) formaldehyde and incubated with 1% bovine serum albumin (BSA)/10 mM phosphate/140 mM NaCl, pH 7.2...

The immunosurveillance mechanisms governing high-risk neuroblastoma (HR-NB), a major pediatric malignancy, have been elusive. We identify a potential role for natural killer (NK) cells, in particular the interaction between the NK receptor NKp30 and its ligand, B7-H6, in the metastatic progression and survival of HR-NB after myeloablative multimodal chemotherapy and stem cell transplantation. NB cells expressing the NKp30 ligand B7-H6 stimulated NK cells in an NKp30-dependent manner. Serum concentration of soluble B7-H6 correlated with the down-regulation of NKp30, bone marrow metastases, and chemoresistance, and soluble B7-H6 contained in the serum of HR-NB patients inhibited NK cell functions in vitro. The expression of distinct NKp30 isoforms affecting the polarization of NK cell functions correlated with 10-year event-free survival in three independent cohorts of HR-NB in remission from metastases after induction chemotherapy (n = 196, P < 0.001), adding prognostic value to known risk factors such as N-Myc amplification and age >18 months. We conclude that the interaction between NKp30 and B7-H6 may contribute to the fate of NB patients and that both the expression of NKp30 isoforms on circulating NK cells and the concentration of soluble B7-H6 in the serum may be clinically useful as biomarkers for risk stratification.

We analyzed the status of retinoblastoma and p53 genes in 10 human hepatoma cell lines. Polyclonal anti-peptide antibodies generated against peptides homologous to COOH-terminal and leucine-zipper domains of the retinoblastoma protein allowed us to identify two cell lines (Hep 3B and FOCUS) with abnormal expression. The same cell lines have both lacked p53 expression. In contrast to the retinoblastoma gene, the expression of the p53 gene was abnormal in six additional cell lines. Indeed, only the Hep G2 hepatoblastoma cell line (and its derivative Hep G2/2215) appeared to have normal p53 and retinoblastoma gene expression. Our studies indicate that p53 abnormalities are common but retinoblastoma gene aberrations are rare in human hepatoma cell lines.