Expression And Mechanism Of IGFBP-7 In Human Colorectal Carcinoma

BACKGROUNDColorectai Cancer (CRC) is a common gastrointestinal malignancy which threatensthe health of human. Worldwide, colorectai cancer is the third most frequent occurring cancer in both sexes and the second most common cause of cancer-related death. The WHO estimates that 945,000 new cases occur annually, with 492,000 deaths, approaching an individual lifetime risk of 5% in developed countries. Improved treatment and efficient surveillance contributed to control the disease, however, theoverall 5-year survival rate is still poor (WHO, 2000) .The majority of colorectai cancer is sporadic, accounting for 88-94% of all CRCs. The rate of CRC in inflammatory bowel disease and in hereditary colorectai cancer is only1-2% and 5-10%, respectively (Weitz et al. 2005) . The genetic component of the risk of developing CRC has been estimated at 35%, with a 95% confidence interval 10-48% (Lichtenstein, 2000) . Susceptibility to CRC is conferred by hereditary cancer syndromes but also complex genetic traits and environmental determinants (Baglioni and Genuardi, 2004) , e.g. there is epidemiological evidence for anassociation between type 2 diabetes, insulin therapy and CRC (Limburg et al. 2005,Yang et al. 2004) .IGFs (Insulin-like growth factors) regulate cell proliferation, differentiation andapoptosis involving normal and cancerous processes by systemic, hormonal and local paracrine effects in high concentrations in the circulation and in the extracellularfluids (LeRoith, 2003) . IGFBPs (Insulin-like growth factor-binding proteins) areresponsible for affecting the half-lives and bioavailability of the IGFs in the circulation and in the extracellular fluids via IGF-dependent or IGF-independent effects under certain conditions. This involves both physiological and pathologicalprocesses (Hwa, 1999) .IGFBP-7, also named IGFBP-related protein 1 (Hwa, 1999), Mac25 (Murphy, 1993),tumor derived adhesion factor (TAF) (Akaogi, 1994) and prostacyclin-stimulatingfactor (PSF) (Yamauchi, 1994), is the first member of the low-affinity IGFBP family.It might have particular biological properties independent of IGFs, which may be different from other members of the high-affinity IGFBPs. It is unclear whether their different affinity with IGFs dominates their roles in the carcinogenesis or the other processes. Recently, IGFBP-7 has received much attention in different cancers(Tennant et al. 2003, Landberg et al 2001, Komatsu et al. 2000) , which suggestedthat IGFBP-7 could be a potential tumor-suppressor gene. However, to date, there are several publications about IGFBP-7 in CRC, mostly suggesting that the gene may actas a tumor promoter or oncogene (Umeda et al. 1998, Adachi et al. 2001, Shao etal .2004) . Through IHC (immunohistochemistry), Shao et al detected the proteinexpression of IGFBP-7 in the Chinese samples. The higher expression in the colon tumor tissues was found compared with the normal colon tissues and the cancer cells located in the invasive front of the cancer nest showed stronger staining of IGFBP-7than those surrounding the lumen, suggesting this gene could have the character of oncogenes. Between the colon solid tumor and cancer cell lines, the difference of the expression character of IGFBP-7 could derive from two reasons: firstly, the development of solid tumors are regulated by the many systemic and local factors in vivo; secondly, the expression of IGFBP-7 in the different ethnicities may be different because the earlier publications about IGFBP-7 in CRC researched the Asian patients' samples and the used cancer cell lines derived from Caucasion. Therefore, the role of IGFBP-7 in colorectal cancer (CRC) is still inconclusive.PURPOSETo analyse the expression of IGFBP-7 at both mRNA and protein levels and explore the mechanism of downregulation of IGFBP-7 in CRC.METHODSemi-quantitative RT-PCRTotal RNA was prepared from the CCD-33Co (normal colon cells) and 8 colon cancer cell lines. The primers for RT-PCR amplification were based on the following sequence of IGFBP-7 (Genbank Accession Number NM₀01553). Through RT-PCR,...