Influence of KRAS activation in the colorectal cancer immunosurveillance escape

• Autor(a) principal: Machado, Ana Luísa Marinho da Cunha
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.22/13957
• topic: Colorectalcancer; tumormicroenvironment; immunecells; immunosurveillance; immuneescape; immunotherapy

The imune system as a host defense system watches the cell growth and division, eliminating cells with antigens different from those present in healthy cells. However, some transformed cells have the capacity, through various mechanisms, to escape the immune system. Genomic instability and some mutations are pointed as possible mechanisms supporting the imune surveillance escape,asisthecaseofoncogenicmutations. KRAS mutation is presente in about 40% of cases of colorectal cancer and confers to the tumor a greater potential for malignancy. It is known that KRAS and BRAF mutant cancer cells regulate the recruitment, activation,and differentiation of imune cells,promoting tumor evolution by ensuring leakage to the immune system and increasing the proliferative potential. Few evidences highlight an association between a KRAS mutation and myeloid cells, mainly macrophages and neutrophils infiltration. However, the mechanism which determines this interaction remains unclear. To investigate how the KRAS and BRAF mutations can influence the immune response, either by regulating the expression of immunomodulatory molecules, leading to altered crosstalk between the tumor and the immune system, or by regulating immune cell infiltration. In our work, a series of immunomodulatory molecules were analyzed by flow cytom-etry in a panel of KRAS and BRAF mutant colorectal cancer cells in which KRAS/BRAF was silenced by small interfering RNA. Additionally, the influence of chemotherapy and IFN-Y administration, wich is a non-consensual possible therapy, in the expression of immune checkpoints molecules was also evaluated. It was also performed immunohistochemistry staining of F4/80 to access the in vivo infiltration and distribution of macrophages i the mouse colonic epithelium. Preliminary results suggest that KRAS silencing lead to the alternation of some molecules involved in the crosstalk with the immune system cells, such as macrophages and lymphocytes, as long as BRAF silencing did not cause any alternation. Additionally, in some cases, chemotherpy and IFN-y administrationshowed to have some influence on the upregulation of theses immune molecules expression, wich was impaired by KRAS silencing. On the other hand, KRAS mutation, was not capable to increase the macrophage infiltration in the mouse colon epithelium. KRAS activation seems to be capable of regulating the expression of surface markers, wich can regulate and suppress the immune response against cancer cells, and to influenc the macrophage infiltration whwn combined with another frequent mutation.