The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras

RING1 interacts with multiple Polycomb-group proteins and displays tumorigenic activity

Polycomb-group (PcG) proteins form large multimeric protein complexes that are involved in maintaining the transcriptionally repressive state of genes. Previously, we reported that RING1 interacts with vertebrate Polycomb (Pc) homologs and is associated with or is part of a human PcG complex. However, very little is known about the role of RING1 as a component of the PcG complex. Here we undertake a detailed characterization of RING1 protein-protein interactions. By using directed two-hybrid and in vitro protein-protein analyses, we demonstrate that RING1, besides interacting with the human Pc homolog HPC2, can also interact with itself and with the vertebrate PcG protein BMI1. Distinct domains in the RING1 protein are involved in the self-association and in the interaction with BMI1. Further, we find that the BMI1 protein can also interact with itself. To better understand the role of RING1 in regulating gene expression, we overexpressed the protein in mammalian cells and analyzed differences in gene expression levels. This analysis shows that overexpression of RING1 strongly represses En-2, a mammalian homolog of the well-characterized Drosophila PcG target gene engrailed. Furthermore, RING1 overexpression results in enhanced expression of the proto-oncogenes c-jun and c-fos. The changes in expression levels of these proto-oncogenes are accompanied by cellular transformation, as judged by anchorage-independent growth and the induction of tumors in athymic mice. Our data demonstrate that RING1 interacts with multiple human PcG proteins, indicating an important role for RING1 in the PcG complex. Further, deregulation of RING1 expression leads to oncogenic transformation by deregulation of the expression levels of certain oncogenes.

Application of the polymerase chain reaction (PCR) to quantify micro-metastasis in an experimental animal

In vitro cultured r/mHM-SFME-1 cells were injected into the hind foot pads of Balb/c mice. Metastasis was detected in the lungs of tumor-bearing mice by means of both PCR and histological methods. Primers for the PCR were set to amplify a 128 bp exon-1 sequence of the human c-Ha-ras1 gene which had been introduced into the cells. Resulted PCR bands were densitometorically quantified using a bioimage analyzer, and more than 1 x 10(4) tumor cells were detectable in the mouse lung. The number of tumor cells per lung estimated from the amount of PCR products was 1 x 10(5), 15 x 10(5), 1 x 10(5) and 40 x 10(5) on days 7, 14, 21 and 28 respectively after the tumor injection. No metastases were histologically observed on days 7 and 14. Then, the possibility of using this model system for evaluation of a treatment against micro-metastases is discussed.

Transfection of metastatic capability with total genomic DNA from human and mouse metastatic tumour cell lines

From a large series of experiments involving transfer of high molecular weight total genomic DNA from highly metastatic human and mouse tumour cell lines to other mouse tumour cell lines we have derived a few cell lines with greatly augmented metastatic properties. In one of these experiments the transfected cell line (designated AH8 Test) not only colonised the lungs but also formed secondary tumour colonies in several extrapulmonary sites including the skin, skeletal muscles, bone, liver diaphragm, spleen and heart. There were no qualitative and quantitative effects of this magnitude when we used DNA from several non-metastatic or non-tumourigenic sources. Secondary transfection of metastatic capability with DNA obtained from a metastasis formed by one of the primary transfectant lines (AH8 Test) has also been accomplished. Concomitant transfer of human DNA through both transfection cycles in this experiment was confirmed by a variety of methods including Southern blot analysis, in situ hybridisation and polymerase chain reaction (PCR) amplification of DNA using primers recognising human-specific Alu repeat sequences. The findings offer opportunities for the isolation of sequences programming metastatic behaviour and we have cloned and sequenced a fragment of human DNA, which has not been previously characterised, from the transfected cells.