| Objective:Growth hormone (GH)/Insulin like factor1(IGF-1) are the most important regulators of postnatal growth and development. The epidemiological studies, however, showed that the colorectal cancer incidence in acromegalic patients who has excessive GH secretion is18times higher than in the general population. While the dwarf people who have inadequate secretion of GH are resistant to several types of cancer. To investigate the functions of GH/IGF-1axis in oncogenesis and development of colorectal cancer,-in this study, a model of colitis-associated colorectal cancer was induced in dwarf and WT lewis rats by using azoxymethane/dextran sodium sulfate (AOM/DSS). The molecular mechanisms were studied in vivo and in vitro.Methods:1?A model of colorectal cancer was prepared in dwarf and WT lewis rats by intraperitoneal injections of AOM twice a week, followed by drinking water containing2%DSS for another week, and repeated for4cycles. At the end, the rats were killed and the size and numbers of colorectal tumor were measured.2?The change of IGF-1level after AOM/DSS treatment were tested by ELISA.3?The mRNA expression of c-myc?cox2?IGF-1?ILlb?P27in colorectal endothelial cells and tumors were analyzed by quantitative PCR.4?The influence of the serum from dwarf and WT rats on proliferation of HCT116cell line were determined by MTT assay and cell cycle were detected by FCM (flow cytometry).5?The molecular mechanisms of GH/IGF-1on apoptosis, cell cycles and cell signal transduction were studied by GH simulation or GH/IGF-1-transfected colorectal cancer cells. And the target protein expression and phosphorylation level were also detected by Western Blot. Results:We found dwarf rat can resist carcinogenesis by AOM/DSS treatment; the incidence rate of colorectal cancer is much lower in dwarf rat than in wild type as well as tumors size. And the1GF-1concentration in dwarf rat is only53.4%of the wild type. Furthermore, after inducing, the plasma IGF-1concentration of WT increased180%. while dwarf rat can resist the up-regulation by slightly increased16%. And it is only about22%of WT induced group IGF-1concentration. The expression level of c-myc, COX-2were much lower in dwarf colorectal epithelial cells (29.8%?52.4%respectively), while P27was higher than wild type. Also in tumor tissues, the level of c-myc, cox-2, IL1b were significantly lower in dwarf rat group. The P27expression was high in dwarf rat than wild type (125.7%).Dwarf rat serum has significantly weaker proliferation effect on colorectal cancer cell than wild type, which can be offset by exogenous IGF-1. The colorectal cancer cell which were cultured by dwarf rat serum were arrested in GI phase (55%vs.39%, P<0.001) and had a lower proliferating index than cultured in wild type serum (45%vs.61%, P<0.001).By Western Blot, we found all the detected colorectal cancer cells have high expression level of growth hormone receptor (GHR) and insulin like factor ? receptor (IGF-1R) in vitro. GH (200ng/ml) can promote cell into the cycle and inhibit apoptosis mainly through phosphorylation on Jak2(56%, P<0.05), Stat3/5(240%,<0.001;250%, P<0.05), and it also can increase the expression level of IGF-IR(70%). IGF-1can phosphorylate GSK-3b by activated Akt (up-regulated960%) through IGF-1R/EGF-R signal pathway. However, phosphorylated GSK-3b (up-regulated50%) can inhibit the degradation of ?-catenin, thus causes the deposits in the nucleus and later triggers many oncogene transcription. In addition. IGF-1may facilitate metastasis by up-regulating expression of MMP-7(48%) which only exists in tumor cells.Conclusions:The results suggested that deficiency of GH/IGF-1can significantly resistance the occurrence of colorectal cancer induced by chemical carcinogens. GH and IGF-1can promote cancer cells proliferation quickly by impulsing them into cell cycles, and also prevent apoptosis of colorectal cancer cell by activating Akt signaling. |
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