Polymorphism and expression of NF-κB in relation to susceptibility and prognosis of colorectal cancer patients

Abstract: Normal human cells are strictly controlled in their environment by extrinsic and intrinsic factors. Despite this, some cells begin to develop into cancer cells, and if this process is allowed to continue, it will develop into cancer disease. To become cancerous, a cell must break several biological barriers. Two important barriers are apoptosis and cellular growth control.Cancer is a multifactorial disease caused by environmental and hereditary factors. The incidence of colorectal cancer varies among different populations around the world. Sweden has a history of a relatively high incidence of colorectal cancer, whereas its incidence in China is relatively low.Nuclear factor kappa B (NF-κB) is a transcription factor protein family, regulating genes involved in several aspects of cancer development. In human cells five members have been identified: NFKB1 (p105/p50), NFKB2 (p100/p52), RelA (p65), RelB and c-Rel. They normally form homo- or heterodimers in the cytoplasm of the cells, where they are in an inactive state by binding to inhibitory proteins, I kappaB-α, -θ and -ε and Bcl-3. Stimulatory signals, both intrinsic and extrinsic, lead the inhibitory proteins to be phosphorylated, which marks them for degradation. On activation, NF-κB proteins are often posttranslationally modified.In the first project, we investigated the role of a polymorphism in the promoter region of NFKB1 gene. The polymorphism is a 4-basepair insertion/deletion located 94 basepairs upstream of the gene (-94ins/delATTG). It does not seem to alter the amino acid sequence of the protein and therefore does not alter the function of the protein itself. Instead, it alters the regulation of the protein transcription. The aim of the present study was to investigate whether the polymorphism was related to cancer risk or clinicopathological variables. We found that this polymorphism increased the risk of sporadic colorectal cancer in a Swedish population but not in Swedish populations with a family history of colorectal cancer or in Chinese population.In the second project we studied an 8-basepair insertion/deletion polymorphism in the promoter region of NFKBIA gene coding for the nuclear factor kappa B inhibitory protein, IκBα. This polymorphism is located 708 basepairs upstream of the gene (-708ins/del8). The aim of the study was to investigate whether the polymorphism was related to cancer risk or clinicopathological factors. We found that this polymorphism was very rare in a Swedish population of colorectal cancer patients and controls and was totally absent in a Chinese population of patients and controls. Our conclusion is that this polymorphism is too rare to have a major impact on colorectal cancer incidence in the two populations.In the third project we studied levels of p65 phosphorylated at Serine-536 in colorectal cancers in a Swedish population. After activation and IκB phosphorylation/degradation, p65 is phosphorylated at Serine-536. This phosphorylation is involved in regulating transcriptional activity, nuclear localisation and protein stability. The aim of the study was to investigate whether the expression of the phosphorylated protein correlated to any clinicopathological variables, including survival. The expression of p65 phosphorylated at Serine-536 increased from normal mucosa to primary tumour, but no further increase to lymph node metastases was found. We did find, however, that the strong expression in the cytoplasm was correlated to worse survival among the patients, independent of gender, age, tumour location, stage and differentiation.In the fourth project we continued to study p65 phosphorylated at Serine-536. In this project, however, we studied the expression in a population of rectal cancer patients who participated in a Swedish clinical trial of preoperative radiotherapy. The aim of the study was to investigate whether the expression correlated to response to radiotherapy or to clinicopathological and some biological factors. We found that the expression was increased from normal mucosa to primary tumour, but detected no further increase from primary tumour to lymph node metastases. We found that the expression of p65 protein phosphorylated at Serine-536 was positively related to expression of TEM1, FXYD-3, PRL, p73 and MAC30 in the group of patients who received radiotherapy. Although no such relationship was seen in the group of patients that had not received radiotherapy, we did not find that the expression of p65 protein phosphorylated at Serine-536 was directly related to the clinical response to radiotherapy.In summary, the -94ins/delATTG polymorphism in the promoter region of NFKB1 gene increases the risk of sporadic colorectal cancer in Swedish but not in Chinese populations. The -708ins/del8 polymorphism in the promoter region of the NFKBIA gene is too rare to have a major impact on colorectal cancer incidence in Swedish and Chinese populations. Strong expression of p65 protein phosphorylated at Serine-536 is independently related to worse survival in Swedish colorectal cancer patients, and the expression is positively correlated to biological factors associated with more malignant features of tumours in rectal cancer patients who received preoperative radiotherapy.