The Expression and Significance of Drainderived Neurotrophic Factor (BDNF) and Its Specific Receptor Trk B in Colon Cancer Cells

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1 The Expression and Significance of Drainderived Neurotrophic Factor (BDNF) and Its Specific Receptor Trk B in Colon Cancer Cells Yi Liu, Lunhui Zhang, Liang Xu * ABSTRACT This paper aims at analyzing the expression and significance of the brain-derived neurotrophic factor (BDNF) in colon cancer cells. The expressions of BDNF have been detected in both of the colon cancer cell lines and the normal intestinal epithelial cell lines. The Colon cancer cell line has a high expression of the Trk B while it has no expression for the BDNF. The normal intestinal epithelial cell line HIEC has no expression for BDNF and low expression for Trk B. The proliferation rate by the BDNF increases gradually along with its increasing concentrations. Under the same concentration condition, the tumor proliferation rate by swollen tyrosine kinase receptor B gradually increases over time. BDNF can facilitate the proliferation of human colon cancer cell lines. Key Words: Brain-derived Neurotrophic Factor, Specific Receptor B, Colon Cancer Cell DOI Number: /nq NeuroQuantology 208; 6 (6): Introduction The brain-derived neurotrophic factor (BDNF) is a protein with a molecular weight of approximately 4 ku. Its major receptor is the tyrosine kinase receptor B (Trk B), which consists of two types: the full-length type and the truncated type including three subtypes. The fulllength Trk B is the main functional receptor for BDNF to combine to exert its physiological functions (Tartaglia et al., 995). The rectal cancer as a common malignancy, with its rising incidence and death rate, threatens people's health and safety. Brain-derived neurotrophic factors (BDNF) is widely found in the central nervous system. Its specific binding receptor is tyrosine kinase receptor B (Trk B), which can activate multiple cell signaling pathways. In addition to providing nutritional support to neuronal cells, BDNF also promotes the differentiation, growth, regeneration and repair of the nervous system. BDNF acts on adipose tissue to modulate the synthesis and secretion of leptin. Such modulation is called the BDNF/Leptin axis. It has been demonstrated that the BDNF is closely related to the development of several types of cancers, including the neuroblastoma, glioma, liver cancer, prostate cancer, pancreatic cancer, nephroblastoma, lung cancer and multiple myeloma etc. (Zhang et al., 994). BDNF is a protein of 32 ku with glycosylated N-terminus at its initial synthesis. Then its amino acid residue of about 28 ku is cut out within the cell and the BNDF is secreted extracellularly which is about 4 ku. However, a few of BDNF is also secreted in the form of precursors with corresponding physiological functions. BDNF receptor Trk B is a type of the tyrosine kinase receptor consisting of two types: the full-length type and the truncated type including three subtypes. The full-length Corresponding author: Liang Xu Address: Department of Gastrointestinal Surgery, The Affiliated Hospital of Southwest Medical University, Luzhou , China @qq.com Relevant conflicts of interest/financial disclosures: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received: 7 March 208; Accepted: 4 May 208

2 Trk B is the main functional receptor for BDNF to combine to exert its physiological functions. As a brain-derived neurotrophic factor, BDNF, as its name suggests, provides nutritional support for neuronal cells. In addition, BDNF also promotes the differentiation, growth, regeneration, and repair of the nervous system. With the same physiological function as leptin, the BDNF facilitates the growth and differentiation of normal cells, only it targets mainly neuronal cells. Now it is also found that it promotes the development of the tumor cells. As mentioned earlier, BDNF is closely related to various human tumors. With its broad distribution in the nervous system and its function of facilitating neovascularization, the BDNF creates a favorable condition for tumor metastasis. Some experiments have shown that the BDNF promotes the neovascularization in vivo and synergistically functions with the vascular endothelial growth factor (VEGF). Some data also show that BDNF in the neuroblastoma cell line promotes the neovascularization by activating the PI3K-Akt signaling pathway to up-regulate the VEGF expression and secretion. Its inhibition of anoikis also facilitates the tumor cell invasion and metastasis. Colorectal cancer as a common malignancy has led to an increasing number of cases and seriously jeopardizes the health and safety of the people. At present, the research of BDNF s effects in tumors, especially its significant effects in the cell proliferation, angiogenesis and metabolism, has demonstrated the important role it plays in the occurrence and development of tumors. In particular, the research of the effects of BDNF and its receptors on the colorectal malignancies still has great potential. It is believed that the deepening of research will further clarified their function mechanisms with tumors, which will be a theoretical basis for the prevention and treatment of colorectal cancer, high-risk population screening and clinical diagnosis and prognosis. Methods Experimental materials, instruments and reagents The human colon cancer cell line DLD- and normal human intestinal epithelial cell line HIEC were both donated by the Cancer Center of Sun Yat-sen University (National Key Laboratory of South China Oncology). Both of the cell lines are placed in the DMEM medium containing 0% fetal bovine serum and incubated at 37 C in a 5% CO2 incubator. The main experiment instruments are optical microscopes, carbon dioxide incubators, large-capacity centrifuges, refrigerated centrifuges, microplate readers, electrophoresis meters, and electro-transformers. Reagents include rabbit anti-human BDNF monoclonal antibody (2960-) and rabbit anti-human Trk B monoclonal antibody (335-). Method The human colon carcinoma cell line DLD- and normal human intestinal epithelial cell line HIEC were obtained and routinely cultured and passaged. Western blot method was used to detect the expression of BDNF and Trk B in human colon cancer cell line DLD- and normal human intestinal epithelial cell line. The microplate reader MTT method was used to detect the effect of BDNF on the proliferation and growth of human colon cancer cell line DLD- and the effect of BDNF on cytotoxicity of 5-Fu cells. Statistical method SPSS 3.0 statistical software was used to process the data. All s of data are presented as mean ± standard deviation (X±s). The comparison of quantitative data was performed with one-way ANOVA with P< as the difference which is statistically significant. Results and Discussion Expression of BDNF and Trk B in colon cancer cell line DLD- and normal intestinal epithelial cell line HIEC Colon cancer cell line DLD- has high expression for Trk B, while the normal intestinal epithelial cell line HIEC has low expression for Trk B. (Figure ). Both of the colon cancer cell line DLD- and normal intestinal epithelial cell line HIEC BDNF has no expression for BDNF (Figure 2) DLD- DLD- HIEC Figure. The expression of Trk B DLD- HIEC Control Figure 2. The expression of BDNF 82

3 Table. Effect of BDNF on DLD- cells for, and ing Table 2. The tumer proliferation rates of BDNF for, and ing 0 6.% 7.8% 3.04% 36.64% 0 5.2% 3.65% 20.35% 33.50% 0 7.0% 5.29% 26.54% 27.8% 0 0.7% 2.50% 23.35% 29.0% % 9.20% 6.56% 9.84% 0 3.6% 0.99% 4.93% 7.30% %.57% 20.46% 25.58% 0 0.4% 6.7% 30.73% 52.26% 0 2% 9.86% 40.4% 60.45% % 37.96% 66.67% 93.83% % 45.69% 67.98% 77.53% % 7.5% 53.40% 50.65% 0 4.9% 23.82% 33.2% 50.73% % 25.20% 48.72% 64.24% % 4.06% 54.98% 66.63% % 43.68% 64.80% 66.83% % 37.42% 38.82% 56.3% % 69.9% 6.95% 75.09% % 3.34% 97% 95.92% % 0.60% 4.7% 54.9% % 39.00% 58.7% 69.3% Effect of BDNF on the proliferation and growth of colon cancer cell line DLD- The effects of BDNF on the proliferation of colon cancer cell line DLD- under different concentration condition and at different times are shown in Table, which can be converted into tumor proliferation rates (Table 2). The tumor proliferation rate gradually increases with the rising concentration. The proliferation rate of all s with concentration higher than μg/m L are significantly higher than that of the blank Table 3. The statistical analysis of BDNF effects on DLD- cells p> ing ± ± ± Table 4. BDNF on the inhibition of 5-Fu in DLD- cells for, and ing BDNF +(5- (5-Fu) Fu)25μg/ml 25μg/ml Table 5. The tumer inhibition rates of leptin and BDNF with 5-Fu for, and ing BDNF +(5- (5-Fu) Fu)25μg/ml 25μg/ml % 35.35% % 46.36% % 50.77% % 42.89% % 45.30% % 37.4% % 43.0% % 6.48% % 67.03% % 72.28% % 69.74% % 7.06% % 67.60% % 68.20% % 86.86% % 89.5% % 83.64% % 89.37% % 89.82% % 89.60% % 88.3% (p<). The s with the concentration lower than does not 83

4 present a significant increase. The comparison of μg/ml and μg/ml shows a significant increase in proliferation (p<). With the same concentration, the tumor proliferation rate gradually increases over time. With various concentration, BDNF s effects on the proliferation rate are significantly different during and (p<), with no significant difference during and (p>) (Table 3). The results of the effects of BDNF on the cytotoxicity of 5-Fu cell are shown (Table 4), which are converted into tumor inhibition rates (Table 5). Conclusion and outlook In our experiment, it is also detected with Western Blot that there are expressions of Trk B in both of the colon cancer cell line DLD- and normal intestinal epithelial cell line HIEC, and low expression of BDNF in the normal intestinal epithelial cell line and there is no expression of BDNF in both of the two cells. The investigators also found BDNF and its receptor in the tumor cells in multiple myeloma patients, and BDNF expression was also found in myeloma cell lines, facilitating the growth of tumor cells (Amemori et al., 2007). The same expression result is found by some researchers with Western blot in multiple bone marrow cell lines (Rouetbenzineb et al., 2004). In the study of liver cancer, it has been confirmed by some scholars that the expression level of Trk B in Hep G2 cell line is equivalent to that of NB cell, while there is only mircroexpression of Trk B in normal liver cell L- 02. In another experiment, the researchers found expressions of BDNF and Trk B m RNA in liver cancer cell line Bel-7402, whereas no expression in L-02 (Aparicio et al., 2005). In the experiment of BDNF promoting the proliferation of human colon cancer cell line DLD-, BDNF of different concentrations were used to treat cells and the growth of tumor cells were observed during different periods (,, and ). The experimental results showed that the tumor proliferation rate increased with the increasing concentrations of BDNF ( μg/ml, μg/ml, μg/ml, μg/ml), and its effects on the proliferation were evident with concentration higher than μg/ml. With the same concentration, the proliferative rate of tumors gradually increased over time, with such effect at 72 hours significantly higher than that at 24 hours. The facilitating effects of BDNF on the proliferation of colon cancer cell line DLD- was also concentration and time dependent. In the subsequent experiments, it was also found that BDNF ( ) reduced the cytotoxicity of 5-Fu, and significantly decreased the tumor inhibition rate of 5-Fu during the periods of 24 h, 48 h, and 72 h (p<). In other tumor cells, such effect of BDNF has also been confirmed. Some researchers mentioned that in patients with liver cancer, BDNF serum level was increased, and such level was positively correlated with platelet counts. However, these clinical data have not yet been published. In vitro experiments, it is also confirmed that BDNF promotes the proliferation of multiple hepatocellular carcinoma cell lines by up-regulating Hsp 90 and cyclin D (Cao et al., 200). Researchers believe that BDNF can at least mediate tumor-associated biological behaviors, including promoting proliferation and inhibiting apoptosis by activating three signal transduction pathways of PI3k-Ak T, RAS-MAPK, and PLc-γ in cells (Stattin et al., 2004). The occurrence of colorectal cancer involves a number of dysfunctions in intracellular gene regulation, such as cell proliferation, angiogenesis, apoptosis, cell cycle, and cell immortality. The next step is to further study the genetic alterations of colorectal cancer cells impacted by BDNF, and to detect with gene chips the genes that experience changes in the cells. 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