Progression of colorectal cancer is associated with multiple tumor suppressor gene defects but inhibition of tumorigenicity is accomplished by correction of any single defect via chromosome transfer.

Abstract

Carcinogenesis is a multistage process that has been characterized both by the activation of cellular oncogenes and by the loss of function of tumor suppressor genes. Colorectal cancer has been associated with the activation of ras oncogenes and with the deletion of multiple chromosomal regions including chromosomes 5q, 17p, and 18q. Such chromosome loss is often suggestive of the deletion or loss of function of tumor suppressor genes. The candidate tumor suppressor genes from these regions are, respectively, MCC and/or APC, p53, and DCC. In order to further our understanding of the molecular and genetic mechanisms involved in tumor progression and, thereby, of normal cell growth, it is important to determine whether defects in one or more of these loci contribute functionally in the progression to malignancy in colorectal cancer and whether correction of any of these defects restores normal growth control in vitro and in vivo. To address this question, we have utilized the technique of microcell-mediated chromosome transfer to introduce normal human chromosomes 5, 17, and 18 individually into recipient colorectal cancer cells. Additionally, chromosome 15 was introduced into SW480 cells as an irrelevant control chromosome. While the introduction of chromosome 17 into the tumorigenic colorectal cell line SW480 yielded no viable clones, cell lines were established after the introduction of chromosomes 15, 5, and 18. Hybrids containing chromosome 18 are morphologically similar to the parental line, whereas those containing chromosome 5 are morphologically distinct from the parental cell line, being small, polygonal, and tightly packed. SW480-chromosome 5 hybrids are strongly suppressed for tumorigenicity, while SW480-chromosome 18 hybrids produce slowly growing tumors in some of the animals injected. Hybrids containing the introduced chromosome 18 but was significantly reduced in several of the tumor reconstitute cell lines. Introduction of chromosome 5 had little to no effect on responsiveness, whereas transfer ot chromosome 18 restored responsiveness to some degree. Our findings indicate that while multiple defects in tumor suppressor genes seem to be required for progression to the malignant state in colorectal cancer, correction of only a single defect can have significant effects in vivo and/or in vitro.

Mutation analysis of the transforming growth factor-β type II receptor in human cell lines resistant to growth inhibition by transforming growth factor-β

“…There is already some evidence for this since the MDA-MB468 breast cancer cell line, which lacks MI and RII mutation, has homozygous deletion of the DPC4 gene which was recently linked to the TGF-b pathway . SW480, which lacks MI and RII mutation, may be another example, since microcellmediated transfer of chromosome 18 restores responsiveness to TGF-b and suppresses its tumorigenicity (Goyette et al, 1992); this is consistent with restoration of DPC4 or another mad-related gene (Eppert et al, 1996), both located on chromosome 18q. Three other cell lines are monosomic for madgenes on chromosomes 5 (JV5-1), 15 (JV15-1, JV15-2) and 18 (DPC4 and JV18-1); KG-1 has monosomy 5, MDA-MB231 lacks both copies of chromosome 15, and SW837 is monosomic for chromosomes 15 and 18 MI, microsatellite instability; adenoca, adenocarcinoma; SCC, squamous cell carcinoma; poly-A, poly-adenine; del A, delete one A; del AA, delete two As; POS, positive; neg, negative; na, not analysed.…”

Targeting gene expression to tumor cells with loss of wild-type p53 function

“…36 This gain of function seems to parallel the oncogenic ability of those mtp53s demonstrated in both in vivo tumorigenicity assays 43,44 and in vitro cell transformation assays of rat embryonic fibroblast cells. 45 The central role of p53 in preventing malignant transformation makes this gene an obvious target for use in cancer gene therapy. The observation that overexpression of wtp53 could lead tumor cells that have lost wtp53 function either to enter apoptosis or undergo cell cycle arrest 46,47 has stimulated various attempts to restore p53 function by re-expressing the wtp53 gene in tumor cells 47,48 or by introducing peptides which mimic the interaction between p53 and a C-terminal antibody, 49 resulting in a restoration of wtp53 conformation and function.…”

Functional identification of LZTS1 as a candidate prostate tumor suppressor gene on human chromosome 8p22

“…Fusion of normal and malignant cells a orded the ®rst evidence that the normal genome may restore the responsiveness of tumor cells to growth controls (Harris et al, 1969). Subsequently, the technique of microcell fusion has been widely used to achieve reversion of the malignant phenotype of certain tumor cells by introducing single normal human chromosomes or subchromosomal fragments (Goyette et al, 1992;Ichikawa et al, 1994;Murakami et al, 1996). Even tumors that have arisen through multiple genetic alterations on di erent chromosomes have been reverted to a less tumorigenic phenotype, indicating that introduction of a single TSG may be su cient to suppress tumor growth.…”