Vírus Oncogênicos e Câncer Prof. Dr. Aguinaldo Roberto Pinto Laboratório de Imunologia Aplicada MIP/CCB/UFSC

Câncer Hipócrates, por volta do ano 400 a.C Câncer: As veias que irradiam a partir de alguns tumores de mama assemelham-se com as pernas de um caranguejo. Ele deu à moléstia o nome de karkinoma (carcinoma), palavra grega que também significa caranguejo, e a mesma associação chegou ao latim.

Células cancerosas ou tumorigênicas variantes de células normais que perderam a habilidade de controlar seu crescimento com as seguintes alterações: Imortalização Transformação Metástase

Fibroblastos normais (monocamada) Fibroblastos transformados (arredondados e em colônias)

Célula Normal Câncer Estima-se que 6-7 eventos devem ocorrer (em ~20-40 anos) para indução do câncer (alterações genéticas e epigenéticas) em certos casos a propensão ao câncer é hereditária

Agentes Carcinogênicos: iniciam ou promovem a formação do tumor Célula Normal Agentes Carcinogênicos: iniciam ou promovem a formação do tumor Célula Tumoral (transformada)

Fatores carcinogênicos Fumo pulmão, esôfago, bexiga e pâncreas Hábitos alimentares (gorduras saturadas e fibras) cólon Obesidade endométrio, cólon, rim, vesícula Álcool trato digestivo e respiratório Vírus

Vírus e Câncer 1908, Wilhelm Ellerman & Olaf Bang 1911, F. Peyton Rous Leucemia de galinha podia ser transmitida por inoculação de filtrado de células tumorais 1911, F. Peyton Rous Sarcoma de galinha – Nobel em 1966

Vírus e Câncer 1908, Wilhelm Ellerman & Olaf Bang 1911, F. Peyton Rous Leucemia de galinha podia ser transmitida por inoculação de filtrado de células tumorais 1911, F. Peyton Rous Sarcoma de galinha – Nobel em 1966 1936, Bittner Carcinoma mamário de camundongos causado por vírus transmitido pela mãe Gross & Friend Vírus relacionado à leucemia de camundongos

Vírus oncogênicos - DNA Doença Câncer Papovaviridae Papillomavirus (HPV) Poliomavírus murino Verrugas, verrugas genitais Câncer cervical e uterino Herpesviridae Vírus Epstein-Barr (HHV4) Vírus do Sarcoma de Kaposi (HHV8) Mononucleose infecciosa Linfoma de Burkitt Carcinoma de nasofaringe Sarcoma de Kaposi Hepadnavirus Vírus da Hepatite B (HBV) Hepatite B Câncer de fígado Adenoviridae Adenovírus Doença respiratória aguda Adenocarcinomas (câncer de tecidos epiteliais glandulares)

Vírus oncogênicos - RNA Câncer Vírus linfotrópico de célula T humana (HTLV-1; HTLV-2) Leucemia de células T do adultos Linfomas Vírus de sarcoma de gatos, galinhas e roedores Sarcomas (câncer de tecidos conectivos) Vírus da leucemia felina (FeLV) Leucemia felina

Tumor Viruses Transformation: Loss of growth control Reduced adhesion Motility Invasion Ability to form tumors - viral genes interfere with control of cell replication and other aspects of the cell phenotype Transformed cells frequently exhibit chromosomal aberrations Viral genes interfere with cell replication control mechanism. NOTE: The early functions of DNA viruses do not make structural proteins but control cellular and viral genome replication.

Classes de genes que quando mutados causam transformação maligna Oncogenes: Genes responsáveis pela transformação maligna de células (~100) A versão celular normal do oncogene é chamada de proto-oncogene (genes celulares homólogos de oncogenes que quando alterados (mutados) levam a transformação) Anti-Oncogenes ou Supressores Tumorais: genes que quando deletados causam aparecimento de câncer (~10)

DNA Tumor Viruses In Human Cancer ONCOGENE A gene that codes for a protein that potentially can transform a normal cell into a malignant cell An oncogene may be transmitted by a virus in which case it is known as a VIRAL ONCOGENE v-onc c-onc X

RNA Tumor Viruses Proto-oncogene A cellular (host) gene that is homologous with a similar gene that is found in a transforming virus Remember: A virus has only one end: to reproduce. This means that the genome and proteins have to be made in large numbers. So many more copies of the v-onc mRNA are made than the c-onc RNA. This over expression may be the basis of the transformation that is seen A cellular oncogene can only induce transformation after mutation some other change in the cell’s genome

Classes de proteínas que são codificadas por oncogenes Fatores de crescimento Classes de proteínas que são codificadas por oncogenes Receptores de Fatores de crescimento Proteínas envolvidadas com a transdução de sinal Fatores de Transcrição

Oncogenes Vírus Oncogene Rous sarcoma virus v-src Simian sarcoma virus v-sis Avian erythroblastosis virus v-erbA or v-erbB Moloney murine sarcoma virus v-mos MC29 avian myelocytoma virus v-myc Kirsten murine sarcoma virus v-kras

Como surgiram os oncogenes retrovirais

DNA Tumor Viruses In Human Cancer Papilloma Viruses cause natural cancers in animals cause benign warts ubiquitous epitheliotropic - most human tumors are malignancies of epithelial cells

DNA Tumor Viruses In Human Cancer Papilloma Viruses 51 types identified - most common are types 6 and 11 Most cervical, vulvar and penile cancers are ASSOCIATED with types 16 and 18 (70% of penile cancers) No final proof that these viruses cause cancer as Koch’s postulates cannot be fulfilled. Papilloma viruses cannot be grown in culture It appears that there is free plasmid in the cell rather than integration EPIDEMIOLOGIAL STUDIES BUT: HPV 16 and HPV 18 do transform human keratinocytes Effective Vaccine (quadrivalent recombinant HPV 6, 11, 16 and 18 proteins made in yeast - Gardasil)

DNA Tumor Viruses In Human Cancer Polyoma Viruses Simian virus 40 - juvenile hamster sarcomas, transformation contaminação de lotes de vacina contra polio Polyoma - mouse leukemia, in vitro transformation Human polyomas (JC and BK) - monkey sarcoma, transformation SV40 was in early batches of polio vaccine Normally these viruses cause lytic infection and transform when they are incomplete Possible association of BK with human prostate cancer Early functions are necessary - ONCOGENES

DNA Tumor Viruses In Human Cancer Adenoviruses Highly oncogenic in animals Adenovirus can be involved in RETINOBLASTOMA and maybe in some other rare cancers Always the same part Early functions E1A region: 2 T antigens E1B region: 1 T antigen E1A and E1B = Oncogenes

DNA Tumor Viruses In Human Cancer Herpes Viruses Considerable evidence for role in human cancer Some very tumorigenic in animals Most people have antibodies against EBV Why some populations get mononucleosis while others get tumors in not known Causes lymphoma in marmosets

DNA Tumor Viruses In Human Cancer Epstein-Barr Virus Burkitt’s Lymphoma Endemic Non-endemic Nasopharyngeal cancer Infectious mononucleosis (glandular fever) Transforms human B-lymphocytes in vitro Most people have antibodies against EBV Why some populations get mononucleosis while others get tumors in not known Causes lymphoma in marmosets Burkitt’s lymphoma: malarial infested regions Nasopharyngeal cancer: China, SE Asia – diet?

DNA Tumor Viruses In Human Cancer Kaposi’s Sarcoma Herpes Virus Human herpes virus – 8 Kaposi’s Sarcoma Herpes Virus Kaposi’s sarcoma

DNA Tumor Viruses In Human Cancer Hepatitis B Virus DNA genome RNA polymerase II RNA Provirus Reverse transcriptase Host enzyme Viral enzyme

DNA Tumor Viruses In Human Cancer Epidemiology: Strong correlation between HBV and hepatocellular carcinoma China: 500,000 - 1 million new cases of hepatocellular carcinoma per year

RNA Tumor Viruses RNA Genome - Retroviruses RNA-dependent DNA Polymerase encoded by virus REVERSE TRANSCRIPTASE RNA genome Reverse transcriptase DNA genome Integrase Integrates Host RNA polymerase II Reverse transcriptase is not a capacity possessed by normal eucaryotic cells Many features are unique to retroviruses Very unusual mode of replication which gives them the potential to transform the cell But when it comes to how these viruses cause neoplasia, they may be very similar to DNA viruses Rous sarcoma virus in chickens was the first retrovirus to be discovered. It causes an aggressive acute cancer in chickens virus host

RNA Tumor Viruses A normal retrovirus has: 3 genes GAG : internal proteins ENV: Envelope glycoproteins POL: Enzymes Reverse transcriptase – RNase H Integrase Protease

RNA Tumor Viruses

RNA Tumor Viruses Retroviruses known to cause human cancer Human T cell lymphotropic virus -1 (HTLV-1) Adult T cell leukemia, Sezary T-cell leukemia Africa, Caribbean, Some Japanese Islands, S. America (Peru, Bolivia) 1-4% of infected people

Como retrovírus causam câncer? “typical retrovirus” R U5 GAG POL ENV U3 R A normal retrovirus has three genes, GAG, OPL, ENV – only these are necessary for the virus to replicate to more virus. Many, however, have another gene that allows them to transform the cell. NOTE: This extra gene is NOT necessary for a productive infection. C.f. DNA tumor viruses in which the oncogene is necessary for BOTH replication and transformation First oncogene to be discovered was the src gene of RSV. It is an extra gene at the 3’ end of the viral RNA Rous Sarcoma Virus R U5 GAG POL ENV U3 R SRC

Substituição de 19 aminoácidos do C-terminal por 12 aminoácidos diferentes

Some retroviruses have an oncogene instead of their regular genes Avian Myeloblastosis Virus R U5 GAG POL MYB U3 R These viruses cannot make all of their proteins and so need a co-infecting “helper” virus Viral oncogenes have three letter names e.g. src, myb Feline Sarcoma Virus (FSV) R U5 dGAG FMS dENV U3 R Avian Myelocytoma Virus (MC29) R U5 dGAG MYC dENV U3 R

Avian Leukosis Virus (causes lymphomas) RNA Tumor Viruses In contrast: R U5 GAG POL ENV U3 R Avian Leukosis Virus (causes lymphomas) No oncogene! – How does it cause a tumor?

ALV can integrate into the host cell genome at MANY locations RNA Tumor Viruses ALV can integrate into the host cell genome at MANY locations but in tumor it is always at the SAME site (or restricted number of sites)

Could C-oncs be involved in NON-VIRAL cancers? RNA Tumor Viruses Could C-oncs be involved in NON-VIRAL cancers?

Cancers often result from gene translocations Burkitt’s Lymphoma 8:14 translocation Break in chromosome 14 at q32 Could the break and exchange of parts of chromosomes bring the c-onc under the control of a very active cell promotor? In Burkitt’s lymphoma there is a 8:14 translocation. Myc is at the break site on chromosome 8. What does it come next to on chromosome 14? myc Acute myelocytic leukemia 7:15 9:18 11:15:17

Oncogenesis by rearrangement Tumor c-onc new promotor Burkitt’s lymphoma myc (8) Ig heavy (8 to 14) Ig light (8 to 2) B-cell chronic lymphocytic bcl-1 Ig heavy (11 to 14) leukemia bcl-2 Ig heavy (18 to 14) Thus in Burkitt’s lymphoma, the myc gene is brought under the control of a Ig promotor which is very active in this lymphocyte. Thus this is similar to putting the cellular oncogene under the control of the very active promotor in the viral LTR Proof that deregulated c-myc may be involved in tumor formation comes from transgenic mice. If a gene consisting of c-myc linked to the Ig promotor is integrated into the chromosomes of these mice there is a high frequency of lymphomas. T cell chronic lymphocytic tcl-1 T cell receptor leukemia (14 inversion) T cell chronic lymphocytic myc T cell receptor (8 to 14) leukemia

have normal regulatory function in many cells Anti-Oncogenes Retinoblastoma gene P53 have normal regulatory function in many cells

Anti-Oncogenes Retinoblastoma Adenovirus E1A Rb Gene Rb protein Rb It is found that in adenovirus cells, the virus E1A gene makes a protein that complexes with a 105kD cellular protein. This turned out to be Rb protein. Binding Rb protein so that it cannot control growth is the same as mutating both copies of the gene for the Rb protein and so the cell continues to replicate Rb 105kD Rb Rb Cell cycle continues Stops replication

Papilloma proteolysis Anti-Oncogenes p53 P53 gene P53 gene P53 gene Hepatitis C Papilloma A similar thing happens to p53 protein in hepatitis C-infected cells and p53 is bound so that it becomes inactive. Again, lack of p53 results in loss of growth control. In papilloma-infected cells, things happen a little differently. In this case the virus makes a protease that destroys p53 protein. Thus, our knowledge of how RNA tumor viruses cause tumors led to the discovery of viral oncogenes. This led to the discovery of cellular oncogenes which in turn led to anti-oncogenes. The discovery of anti-oncogenes showed how DNA tumor viruses cause tumors. P53 P53 P53 Papilloma proteolysis P53 DNA Stops replication replication replication

DNA Tumor Viruses Oncogenes Adenovirus E1A region 2 SV 40 Large T Polyoma Large T BK virus Large T Lymphotropic virus Large T Human papilloma Virus-16 E7 All have a sequence in common Mutations in this region abolish transformation capacity The oncogenes of DNA viruses such as polyoma or adenovirus have been identified to early function genes and all of these seem to have characteristics in common, indeed, they have some sequence similarities and mutations in this common region abolish tumorigenicity

CANSEI!