Virusi u patogenezi tumora

Maligne tumore definira odsutnost dodirne inhibicije, mogućnost metastaziranja u druga tkiva, nekontrolirana dioba i proliferacija stanica. Danas je poznato najmanje 7 virusa čija je infekcija povezana s nastankom tumora: virus hepatitisa B (HBV) i C (HCV), papiloma-virusi, Epstein-Barrov virus (EBV), herpesvirus povezan s Kaposijevim sarkomom (KSHV) i ljudski T stanični limfotropni virus (HTLV), virus humane imunodeficijencije (HIV) te poliomavirus Merkelovih stanica (MCPV). Na transformaciju stanica virusi mogu utjecati: 1) direktnom karcinogenezom i 2) indirektnom karcinogenezom. Direktna karcinogeneza uključuje ekspresiju virusnih onkogena kao i deregulaciju staničnih onkogena i tumor-supresorskih gena. U slučaju dirktne karcinogenze genom virusa može se pronaći u stanicama izoliranim iz tumorskog tkiva. Indirektna karcinogeneza najčešće je uzrokovana uspostavljanjem stanja kronične upale pri čemu se okolna tkiva konstantno oštećuju nastajanjem mutiranih stanica i borbom imunosnog sustava protiv istih. Imunosupresija još je jadan mehanizam indirektne tumorigeneze pri kojem imunosni sustav gubu sposobnost prepoznavanja promijenjenih stanica vlastitog organizma i djelovanja protiv istih. Primjer za direktnu karcinogenezu su hepresvirusi (EBV i KSHV), a za indirektnu najbolji je primjer HIV. Svaki od virusa svojom infekcijom utječe na nastanak pripadajućeg malignog tumora ili više njih. Onkogeni se virusi međusobno razlikuju prema tipovima stanica koje inficiraju, životnim ciklusima i vrsti molekule koja im služi kao genetska uputa, a sve to određuje mehanizam kojim će uzrokovati transformaciju stanica u tumorske.Malignant tumor is generally defined by the absence of touch inhibition, the possibility of metastasis to other tissues, uncontrolled division and cell proliferation. At least 7 viruses today are known to be associated with tumor formation: hepatitis B virus (HBV) and C virus (HCV), papillomavirus, Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), human T-cell lymphotropic virus (HTLV), human immunodeficiency virus (HIV) and Merkel cell polyomavirus (MCPV). Cell transformation can be affected by viruses: 1) by direct carcinogenesis and 2) by indirect carcinogenesis. Direct carcinogenesis involves the expression of viral oncogenes as well as the deregulation of cellular oncogenes and tumor suppressor genes. In direct carcinogenesis, the genome of the virus can be found in cells isolated from tumor tissue. Indirect carcinogenesis is most often caused by the establishment of chronic inflammation in which the surrounding tissues are constantly damaged by the formation of mutated cells and the fight of the immune system against them. Immunosuppression is another mechanism of indirect tumorigenesis in which the immune system loses the ability to recognize altered cells of its own organism and act against them. An example of direct carcinogenesis are hepressviruses (EBV and KSHV), and for indirect the best example is HIV. Each of the viruses with its infection affects the formation of the associated malignant tumor or more of them. Oncogenic viruses differ from each other in the types of cells they infect, life cycles, the type of molecules that serve as their genetic guide, and all this determines the mechanism by which they will cause the transformation of cells into tumors