Monochromosome transfers to Syrian hamster BHK cells via microcell fusion provide functional evidence for suppressor genes on human chromosome 9 both for anchorage independence and for tumorigenicity

Regional mapping of suppressor loci for anchorage independence and tumorigenicity on human chromosome 9

By microcell-mediated chromosome transfer to the malignant Syrian hamster cell line BHK-191-5C, we previously identified two suppressor functions on human chromosome 9 (HSA9), one for anchorage independence and another for tumorigenicity. However, the precise chromosomal locations of these suppressor functions were not determined. The present study was undertaken to define the regional location of these suppressor loci using a panel of microcell hybrids containing structurally altered HSA9 with different deleted regions in the BHK-191-5C background. DNA derived from the cell hybrids was analyzed by PCR for verification of the presence of HSA9 genetic material by amplifying 62 microsatellite markers and 13 genes, covering the entire length of HSA9. Our deletion mapping data on anchorage independent and tumorigenic hybrids suggest that the suppressor function for anchorage independence is located in the region between 9q32 to 9qter. The suppressor for tumorigenicity may be located in one of three deleted regions on HSA9, the first one between the markers D9S162 and D9S1870, the second one between the markers D9S1868 and TIGRA002I21, and the third one between the markers D9S59 and D9S155.

Establishment and characterization of a spontaneously immortalized myofibroblast cell line derived from a human liver angiosarcoma

BACKGROUND/AIM

Fibrosis and/or cirrhosis are present in the precursor stages of most liver cancers. However, little is known about the reciprocal interactions of fibroblasts, mainly responsible for fibrosis, and the other liver cells. We report here the isolation of a new liver myofibroblast cell line from a human liver angiosarcoma and its characterization.

METHODS

The cells were isolated by the explant technique and characterization was performed, on one hand, using immunohistochemical and ultrastructural analysis and, in the other hand, by determining their karyotype, ras and p53 status and their tumorigenic properties.

RESULTS

To date, the cells have undergone approximately 170 population doublings and are still proliferating. Immunohistochemically, they were negative for desmin, smooth muscle myosin, cytokeratin 19 and von Willebrand factor, positive for vimentin and alpha-smooth muscle actin, with an important deposition of fibronectin around the cells. Ultrastructure showed particularly cytoplasmic microfilament bundles. Their chromosome number ranged from 38 to 168 with a bimodal population, near diploid and hypotetraploid. No mutations were found in codons 12, 13 or 61 of Ha-, Ki- and N-ras genes but a homozygous missense mutation in codon 179 (CAT-->CTT) was detected in the p53 gene. They were unable to form foci in soft agar or tumors in nude mice.

CONCLUSIONS

Taken together, these results show that these cells, called BM 2.2.1, exhibited typical myofibroblast-like features. Although they contained a karyotype suggestive of tumoral cells and a homozygous mutated p53 gene, they were not tumorigenic. The nature of these cells and the abnormalities of the p53 gene and the karyotype, suggest that: i) they were a component of the tumor stroma, and ii) they could have been involved in angiosarcoma development. Thus, this cell line may be valuable for the study of cellular interactions in liver carcinogenesis.

A new functional classification of tumor-suppressing genes and its therapeutic implications

Cell fusion studies have demonstrated that malignancy can be suppressed by a single dose of malignancy suppressor genes (MSGs), indicating that malignancy is a recessive phenotype. Correspondingly, it is widely believed that mutational inactivation of both alleles of tumor suppressor genes (TSGs), in familial and sporadic tumors, is the formal proof of the recessive nature of malignancy. Evidence presented here, however, shows that unlike MSGs, identified solely through cell fusion studies with no gene of this class yet cloned, many well-known TSGs have gene dosage effects and inhibit cellular growth in vitro. Moreover, homozygous inactivation of a growth-inhibitory TSG (GITSG) is not directly correlated with malignancy. An alternative interpretation is provided for the loss of wild-type alleles of these genes in the tumors. It is concluded that the MSGs and the GITSGs do not belong to the same class of genes. The functional classification of tumor-suppressing genes has important implications for developing effective cancer therapies.

Isolation of DNA markers for the rat Sai 1 gene for suppression of anchorage independence by using representational difference analysis

We have applied the representational difference analysis (RDA) to isolate genetic markers for a deletion on the rat chromosome RNO5q22-33. This deletion occurred in anchorage independent sublines of a normal rat fibroblast x mouse hepatoma cell hybrid (BS181) (Islam 1989). Normal rat tissue DNA provided the "tester" and the BS181 hybrid DNA the "driver" in the RDA hybridization/selection reactions. Out of twelve RDA derived DNA sequences that were analyzed in detail using a rat X mouse cell hybrid panel for chromosome mapping, nine (75%) were found to represent RNO5 deletions, whereas the other three were new RFLPs mapping to other chromosomes. In two cases, the RDA sequences were also analyzed by fluorescence in situ hybridization (FISH) and found to give distinct signals in the RNOq22-33 region. This result emphasizes teh significance of the previous cytogenetic analysis of this hybrid, which indicated the presence of a gene for the suppression of anchorage independence, Sai 1, in this deletion region. The RDA derived sequences isolated by this work will provide a valuable source of new genetic markers for the further detailed analysis of the Sai 1 deletion region.

p16ink4a gene and hematological malignancies

Progression of eukaryotic cells through major cell cycle transitions is mediated by sequential assembly and activation of regulators, the cyclin-dependent CDKkinases (CDKs). Recent studies have identified different CDK inhibitory genes (CDKis), and two of them, p16ink4a/MTS1/CDKN2 and p15ink4b/MTS2 are both mapped to chromosome 9p21 and inhibit cyclin D-CDK4 and -CDK6 complexes. A feedback regulatory loop involving pRb, p16ink4a, and CDKs seems to regulate G1/S phases transition. p16ink4a and p15ink4b are deleted in high frequency in human cell lines and in some fresh solid tumors. Point mutations of p16ink4a have also been sequenced, especially in familial melanomas and digestive cancers but preferential mechanism of p16ink4a/p15ink4b inactivation seems to be biallelic deletion. In hematological malignancies, homozygous deletions of p16ink4a and p15ink4b occur frequently in acute lymphoblastic leukemia (ALL) (14-40%), lymphoid type blast crisis of chronic myeloid leukemia (CML), and adult T cell leukemia (ATL), but p16ink4a deletions are more frequent than p15ink4b deletions, and hemizygous deletions of either p16ink4a and p15ink4b are rare. In ALL an association of homozygous deletions of p16ink4a and p15ink4b, and T-lineage, 9p abnormalities, and prognostic factors was found in some but not all reports. This review presents recent data on p16ink4a and p15ink4b functions and analyses their implications in hematological malignancies.