Genetic abnormalities and expression of p53 in human colon carcinomas

Expression of cyclin E in colorectal adenomas and adenocarcinomas: correlation with expression of Ki-67 antigen and p53 protein

The expression of cyclin E in human colorectal adenomas and adenocarcinomas was examined immunohistochemically to elucidate the role of cyclin E in the colorectal carcinogenesis. The expression of cyclin E was detected in 25% (91/358) of the adenomas and 56% (149/267) of the adenocarcinomas. The incidence of strongly positive cases was significantly higher in the adenocarcinomas (20%) than in the adenomas (5%) (P < 0.01). Among adenomas, a significant correlation was noticed between the expression of cyclin E and the grade of atypia. The incidence of cyclin E expression was significantly higher in the adenocarcinomas without an adenoma component (62%; 104/169) than in those with this component (46%; 45/98) (P < 0.05). Furthermore, the incidence of the cyclin E expression was higher in stages 1 and 2 carcinoma than in stage 0 and stages 3 and 4 carcinoma. The expression of cyclin E was the most prominent in tumors invading the submucosa and muscularis propria. The expression of cyclin E was significantly correlated with the proliferative activity of the tumor cells measured by Ki-67 antigen expression (P < 0.01). It was also correlated with the expression of p53 protein in the tumor cells (P < 0.01). Overexpression of cyclin E and subsequent deregulation of cell cycle may contribute to the development and early progression of the colorectal carcinomas.

Genetic status and expression of the cyclin-dependent kinase inhibitors in human gastric carcinoma cell lines

Deregulation of cyclin, cyclin-dependent kinases (CDKs) and their inhibitors could have a pivotal role in the development of diverse human cancers. We examined the genetic status and the expression of CDK inhibitors (p21, p27, p16 and p15), CDK2 and cyclins (A, D1 and E) in eight gastric carcinoma cell lines, in comparison with the status of p53 gene alterations. All the cell lines (except MKN-28) that contained a p53 gene abnormality expressed very low or undetectable levels of p21 mRNA, while the cell lines (MKN-45 and -74) with wild-type p53 gene expressed high levels of p21 mRNA. An inverse correlation was found between the level of p21 mRNA and the expression of mRNAs for CDK2 and G1 cyclins. MKN-28 was an exception; it contained mutated p53, and expressed mRNAs for p21, CDK2 and G1 cyclins at high levels. Only MKN-45 and -74, with wild-type p53, expressed considerable levels of p21 protein. Homozygous deletion of the p16 and p15 genes was detected in two (MKN-45 and HSC-39) of the eight gastric carcinoma cell lines, p16 protein was not expressed in three cell lines (MKN-28, MKN-74 and KATO-III), as well as MKN-45 and HSC-39. Rearrangement of the p15 gene was found in TMK-1. Rearrangement of the p27 gene was detected in MKN-45, although the expression of p27 protein was well preserved in all the gastric carcinoma cell lines. The expression of pRb was also preserved in all the cell lines except KATO-III. No obvious correlation was observed between the p53 gene status and the expression of p27 and p16. These findings suggest that abnormal regulation of CDK2/cyclins and CDK inhibitors might be involved in deregulated growth of gastric carcinomas.

Molecular mechanism of stomach carcinogenesis

Gene changes in multiple oncogenes, multiple growth factors and multiple tumor-suppressor genes are observed in stomach cancer. Among them, those most commonly implicated in both well-differentiated adenocarcinoma and poorly differentiated adenocarcinoma are inactivation (mutations and allele loss) of the p53 gene, and activation (abnormal expression and amplification) of the c-met gene. Moreover, they occur at an early stage of stomach carcinogenesis. In addition, loss of heterozygosity (LOH) on chromosome 5q (APC locus) is frequently associated with well-differentiated adenocarcinoma. LOH on chromosome 18q (DCC locus) and LOH of the bcl-2 gene also are common events of well-differentiated adenocarcinoma. LOH on chromosomes 1q and 7q may be involved in the progression of well-differentiated adenocarcinoma. Conversely, the development of poorly differentiated adenocarcinoma, in addition to changes in p53 and c-met genes, requires reduction or dysfunction of cadherin. Overexpression of bcl-2 protein is observed in poorly differentiated adenocarcinoma or signet-ring cell carcinoma. Moreover, the K-sam gene is amplified preferentially in poorly differentiated adenocarcinoma of scirrhous carcinoma. K-sam amplification in scirrhous carcinoma often occurs independently of c-met gene amplification. LOH on chromosome 1p also is relatively common in poorly differentiated adenocarcinoma. Exceptionally, signet-ring cell carcinoma shares APC mutations. There are some differences in expression of the growth-factor/receptor system between well-differentiated adenocarcinoma and poorly differentiated adenocarcinoma. Moreover, interaction between cell-adhesion molecules in tumor cells expressing c-met and hepatocyte growth factor (HGF) from stromal cells is linked with morphogenesis of two histological types of stomach cancer. Intestinal metaplasia and adenoma of the stomach also contain p53 mutations and K-ras mutations or tpr-met rearrangement. Taken together, different genetic pathways of stomach carcinogenesis may exist for poorly differentiated and well-differentiated stomach cancers. Some of the latter may develop by a cumulative series of gene alterations similar to those of colorectal cancer.