[Study of B2 gene structure and its expression in colorectal cancer].

OBJECTIVE

To get a complete cDNA sequence of B2 and evaluate the correlation on structure and expression between B2 and insulin like growth factor binding protein related protein 1 (IGFBP-rP1) in colorectal carcinomas, paired normal tissues, adenomas, tissues adjacent to the tumor, and colorectal carcinoma cell lines.

METHODS

5'RACE (rapid amplification of cDNA end) was applied to get the sequence of the 5' end of B2. Semi-quantitative RT-PCR and immunohistochemistry were used to detect the expression of B2 in colorectal cancer tissues and cell lines (SW480, SW1116, SW620, HCT8, CoLo205 and LoVo).

RESULTS

A sequence of 1,125 bp was obtained by combining the sequence from 5'RACE product and the known sequence of B2. It shared 1,122/1,125 identities with IGFBP-rP1. At the level of mRNA, the expression of B2/IGFBP-rP1 was high in colorectal carcinomas, moderate in adenomas and tissues adjacent to tumor, low in normal tissues (P < 0.05). Five cell lines except SW480 showed no expression of B2/IGFBP-rP1. A significant difference was obtained in the immunoreactivity of B2/IGFBP-rP1 between normal tissue and cancer (P < 0.05). In 28.9% (22/76) samples, cancer cells locating at the invasive front of cancer nest had a stronger staining of B2/IGFBP-rP1 than those surrounding the lumen. These samples had also an increased frequency of lymph node metastases, increased depth of invasion and a stronger staining of B2/IGFBP-rP1 than in other samples (P < 0.05).

CONCLUSIONS

B2 is the same gene as IGFBP-rP1. Overexpression of B2/IGFBP-rP1 may play an important role in the initiation and promotion of colorectal cancer. Its overexpression in invading tumor cells may be linking with an increased potential of invasion.