A benign cultured colon adenoma bears three genetically altered colon cancer oncogenes, but progresses to tumorigenicity and transforming growth factor-beta independence without inactivating the p53 tumor suppressor gene.

We describe the spontaneous progression of a colon adenoma cell line to tumorigenicity and growth factor independence. This system allows direct comparison of biologic stages of malignant progression with alterations of colon cancer suppressor genes and oncogenes. VACO-235, a human colon adenoma cell line, is at early passages nontumorigenic in the nude mouse, unable to grow in soft agar, growth stimulated by serum and EGF, and growth inhibited by TGF-beta. VACO-235 daughter passages 93 and higher have in culture spontaneously progressed to being weakly tumorigenic, but retain all other growth characteristics of VACO-235 early passages. A mouse xenograft from late passage VACO-235 was reestablished in culture as the granddaughter cell line, VACO-411. VACO-411 is highly tumorigenic, clones in soft agar, and is unresponsive to serum, EGF, and TGF-beta. Early passage VACO-235 bears a mutant K-ras allele, bears only mutant APC alleles, expresses no DCC transcripts, and expresses only wild type p53 transcripts. VACO-411 retains the identical genotype, still expressing only wild type p53. Colonic cells after ras mutation, APC mutation, and DCC inactivation remain nontumorigenic and growth factor dependent. Malignant progression involves at least two additional steps, and in VACO-411 can proceed by a novel pathway not requiring p53 inactivation.

Early loss of deleted in colorectal carcinoma gene transcript detected in a group of benign colon adenomas.

We examined the expression of the putative tumor suppressor gene deleted in colorectal carcinoma (DCC) in human colon adenoma tissues and cell lines. One allele of DCC is deleted in 70% of human colon carcinomas, and DCC expression is undetectable in 90% of colon carcinoma cell lines. One DCC allele is also deleted in 50% of human colon adenomas, but results from protein expression studies have differed as to whether complete loss of DCC expression could occur in colon adenomas, or instead correlates with progression of colon adenoma to carcinoma. To further examine the timing of DCC expression loss in colon adenomas, we assayed DCC transcript levels in adenoma cell lines and tissues. We measured DCC expression by a sensitive assay using Southern blot detection of the RT-PCR-amplified DCC transcript. DCC expression was negligible or greatly reduced in 4 of 14 colon adenomas, including 2 of 2 adenoma cell lines and 2 of 12 adenoma tissue samples. These data are the first evidence that expression of DCC transcript can be silenced in colon adenoma cell lines and tissues. These data indicate that loss of DCC expression occurs in some colon adenomas, but is insufficient to drive the adenoma to carcinoma progression.