Unit 3 - Viruses and Cancer Flashcards
What is Cancer?
Cancer: Uncontrolled growth of abnormal cells in the body
- 10^14 cells in the body; chance of individual cell becoming cancerous is ~3x10^-14
- Cancer can develop in almost any organ or tissue (more than 100 types of cancer)
- Cancer caused about 13% of all human deaths worldwide (7.9 million) in 2007
- rates are rising as more people live to an old age
- Three most common cancers in men: Prostate, lung, and colon
- Three most common cancers in women: Breast, colon and lung
What are the causes and risk factors in cancer?
Causes and Risk Factors:
- Carcinogens (asbestos)
- Behavior (alcohol use, smoking)
- Hormones (HRT)
- Psychological stress (?)
- Heredity
- Radiation and UV light
- Physical inactivity/obesity
- Viral infections (10-20% of cancers worldwide
What is the history of cancer viruses and tumors?
- Cancer has afflicted humans throughout history?
- Hipposcrates observed carcinomas (460-370B.C.)
- Percival Pott (1775): chimney sweeps and scrotal cancer caused by soot
- 18th century: 1st cancer hospital in Reims, France; cancer as contagious disease
What and Who was involved in Early cancer Research?
- Ellerman and Bang (1908): demonstrated that “filterable agents” (viruses) could produce tumors in chickens
- Peyton Rous (1911): demonstrated that a cell-free, bacteria-free filtrate could cause sarcomas (slow-growing solid tumors) in chickens
The transmissible agent was a retrovirus, later named Rous sarcoma virus (RSV)
1st identified oncogenic virus (“oncovirus”)
What is Bishop and Varmus?
- RSV genome: gag, pol, env, and src
- Discovered that the src gene is found in the normal DNA of chickens (and later mammals and humans).
- Their work demonstrated that oncogenes are cellular genes that were hijacked by viruses from cells.
- Cause cells to become transformed or cancerous
- 1989 Noble Prize
What is a viral oncogene (v-onc)?
It is a viral gene responsible fo roncogenicity of the virus
What is Proto-oncogene?
Proto-oncogene: cellular genes that promote normal growth and cell division
What is cellular oncogene?
Cellular oncogene: mutated form of proto-concogene that causes tumor formation
What are Tumor suppressor gene?
Tumor Suppressor gene: gene that inhibits conversion of normal cell into a cancer cell
What is Transformation?
Transforation: Change in the morphological, biochemical, or growth protperites of a cell
What is Metastasis?
Metastasis: when a cell or clump of cells separates from a tumor and spreads to another location.
How is the Eukaryotic Cell cycle and cancer involved in one another?
- Interphase (G1, S, G2)
- Mitosis
- Cytokinesis
- “Checkpoints” to monitor and regulate the cell cycle
- G1/S and G2/M
- Regulatory molecules
- Cyclins & cyclin-dependent kinases (CDKs)
- Dysregulation of cell cycle components may lead to tumor formation
What are Telomeres?
- DNA sequences found at the end of chromosomes
- Telomeres become shorter during normal aging
- Short telomere signals cell to stop dividing
- Telomerase: enzyme that synthesizes telomeric DNA (“TTAGGG“) on the ends of chromosomes
- Cancer cells contain increased levels of telomerase activity
- Telomere length never shortens and cell never stops dividing
What are the properties of Cancer or Transformed Cells In vitro (cell culture)?
- Genetic changes—polyploidy, high levels of telomerases
- Immortalization
- Metabolic changes—grow rapidly
- Lack of contact inhibition—cells pile up
- Anchorage independent—loss of adhesion
- Require less serum in medium to grow
- Loss of cell cycle control
- Changes in membrane structure and function
- Tumor-associated carbohydrate antigens
What is involved in properties in Cancer cells in vivo?
- Increased oncogene protein expression due to amplifications, translocations, or mutations
- Loss of tumor suppressor gene function due to deletion or mutation
- Cells divide uncontrollably
- Increased levels of enzymes important for nucleic acid synthesis
- Increased telomerase activity
- Malignant cells avoid host immunosurveillance
What the the different Assays to Detect Transformation?
- Focus-forming assay
- Soft agarose assay
- Reduced serum requirement
What is a Forcus Forming assay?
Focus-forming assay: transformed cells lose contact inhibition and grow on top of each other in dense piles (foci)
What is a Soft agarose assay?
Soft agarose assay: transformed cells can divide and form colonies when suspended in agarose
Wha tis reduced serum requirement?
Reduced serum requirement: transfomred cells can grow in media containing reduced serum (low 0.5% vs. normal 10%)
Since cancer is a Multistep process, what is involved in that multistep process?
- Cells bypass apoptosis
- Cells circumvent the need for growth signals
- Cells escape immunosurveillance
- Cells (tumors) command their own blood supply
- Cells may metastasize
- Tummor suppressor genes lose function
What are some of the viruses that are related to cancer?
- Viruses are associated with 10-20% of cancer worldwide
- At least six viruses are thought to contribute to cancers
- Hepatitis B virus
- Hepatitis C virus
- Human Papillomavirus
- Epstein-Barr virus
- Kaposi’s sarcoma-associated herpesvirus
- Human T-lymphotropic virus types 1 and 2 (HTLV-1 and -2)
What are the molecular mechanisms of virally-induced tumor formation by RNA tumor viruses?
Retrovirus genome
- pol encodes reverse transcriptase (RNA→DNA), integrase, Rnase H, and protease
- gag encodes matrix and core structure proteins
- env encodes “spike” proteins that are embedded in envelope and are critical for attachment
- Repetitive (R) and unique (U) sequences enable DNA copy of genome to be inserted into host DNA
Some retroviruses contain an additional gene (v-onc)
- not an essential gene
- hijacked from genome of host cells during evolution
- encodes a protein capable of inducing cellular transformation
What are the molecular mechanisms of how retroviruses can cause cancer?
Random integration of provirus into host cell DNA:
- Insertion within/near a cellular oncogene (c-onc)
- Insertional activation: abnormal expression of c-onc leads to uncontrolled growth
- Insertional inactivation of cellular tumor suppressor gene leading to uncontrolled cell division
- Integrated v-onc may become activated and transcribed
- Promoting normal cell growth and division; tumor formation
What are Human Retroviruses and how many have been identitfied?
Five human retroviruses have been identified:
- Human foamy virus
- HTLV-1
- Sexually transmitted (male → female)
- Most people infected are asymptomatic carriers
- 2-5% chance of developing Adult T-cell Leukemia (ATL)
- HTLV-2
* Hairy Cell Leukemia - HIV-1*
- HIV-2*
What are DNA Tumor Viruses?
Who discovered it?
How do DNA tumor viruses differ from RNA tumor viruses?
What are oncogenes of DNA tumor virese essential for?
- Richard E. Shope (1930s): discovered 1st DNA tumor viruss
Rabbit fibromas and papillomas; filterable agent caused tumors
- DNA tumor viruses differ from RNA tumor viruses
Structure
Genome organization
Replication strategies
- Oncogenes of DNA tumor viruses are essential viral genes used in replication
Those from small DNA tumor viruses do not have cellular homologs
Most target tumor suppressor genes
- % of transformation < 1:100,000 infected cells
What is Epstein-Barr Virus (EBV)?
- Also known as human herpes virus 4 (HHV-4)
- Named after Anthony Epstein and Yvonne Barr
- Isolated from lymphoma samples collected by Dennis Burkitt (1964).
==Burkitt’s lymphoma
=== Aggessive, malignant cancer similar to leukemia
- Teens usually infected with EBV
- causes mononucleosis (“the kissing disease”)
==Sore throat
==Swollen glands
==Fatigue
==Lack of appetite
==Headache
==White patches in the back of the throat
==Usually not life-threatening
- 95% of the population in the US. between the ages of 35 and 40 are persistently infected with EBV.
Why doesn’t everyone get Burkitt’s lymphoma?
What is Burkitt’s Lymphona and Who gets it?
- Burkitt’s lymphoma (BL) is most common in children in central Africa (30-60% of malignant tumors).
- They suffer from conditions that weaken their immune system (e.g., chronic malaria or AIDS).
- EBV persistently infects B lymphocytes.
- BL is a solid tumor of B lymphocytes.
- BL affects the jaw and very rapidly spreads to the soft tissues and the parotid glands.
- The DNA of BL tumors contain genetic aberrations
- Chromosomal translocations resulting in abnormal regulation of the c-myc gene.
What is the Geographic Distribution of Burkitt’s Lymphoma?
- Tropical zones of Africa, New Guinea, and South America
- Related to temperature (60°F minimum), altitude (< 1,500 meters), and rainfall
What is Kaposi’s Sarcoma-Associated Herpesvirus (KSHV)?
- Also referred to as human herpesvirus-8 (HHV-8)
- Cause of Kaposi’s sarcoma (1872)
- Rare skin cancer
- Virus discovered as the cause of Kaposi’s sarcoma in 1994
- Viral genome encodes a cyclin and a Bcl2 homolog
- Kaposi’s sarcoma occurs most often:
- Elderly men of Mediterranean, Middle Eastern, or Eastern European decent (10-15 males: 1 female)
- AIDS patients (50% risk)
What is Hepatitis B virus (HBV)?
- HBV causes chronic hepatitis that can progress to cirrhosis and liver cancer (HCC).
- Liver cancer is 5th most common cancer
- HBV infects the hepatocytes of the liver.
- HCC tumors in patients infected with HBV usually harbor integrated viral DNA.
- HBV transmitted by infected blood/body fluids
- HBV vaccine was the first vaccine to prevent a cancer.
- Taiwan: carrier state reduced from 9.8% to ~1% in 10 yrs
What are Human Papillomaviruses (HPV)?
- HPV infections are most common among sexually active adults and adolescents.
Most prevalent sexually transmitted disease in the world today
- There are over 100 different types of HPVs (low, medium, and high-risk).
Low-risk types are benign and cause warts or papillomas (e.g., genital warts, warts on hands and soles of feet).
High-risk types cause cervical, vulva, vagina, anus, and penis cancers (e.g., types 16 and 18).
4- to 20-year latent period between infection and cancer
What is HPV Replication?
Viral Life Cell is linked to epithelial cell differentiation
- HPVs infect basal epithelial cells via entry though a break in the skin
- Genome replication and virion assembly occur in nuclues of epithelial cells
Why care about HPV and oncogenesis?
- HPVs may cause 16% of female cancers worldwide and 10% of all cancers
- HPV-16 (50%), HPV-18 (15%), HPV-45 (8%), and HPV-31 (5%) DNA found in nearly all cervical cancers
- HPV genome integrated into host cells
- Inactivate tumor suppressor genes p53 and pRb
- 555,00 new cases of cervical cancer annually, with 310,000 deaths
- Vaccination recommended for both girls and boys
- HPV can be found in semen
- high-risk HPV types are responsible for a large proportion of cancers of the mouth and pharynx in males
What is involved in HPV vaccine Production?
Merck GARDASIL—licensed by FDA in 2006 (HPV-6, 11, 16, and 18)
GSK CERVARIX—licensed by FDA in 2009 (HPV-16 and 18)
Prevents ~70% of cancers
HPV-16/18 virus-like particles (VLPs) produced in yeast
What are Animal DNA Tumor Virus?
- Adenoviruses
- Isolated from human adenoids of children by Rowe in 1953
- Many types of adenoviruses
- 47 types identified by 1989
- Some adenoviruses can cause malignant tumors in baby rodents (e.g., hamsters and mice).
- Adenovirus E1A and E1B genes transform rodent cell lines.
What is the Adenovirus Strucutre?
- 80 nm in diameter
- Nonenveloped
- Icosahedral-shaped
- Knobbed penton fibers projecting outward
- dsDNA (36–38 kb in length)
- Can infect a wide variety of cell types
- chosen as a gene therapy vector
What is Simian Vaculoating Virus-40 (SV-40)
- Isolated from primary African green monkey kidney cells by B.H. Sweet and M.R. Hilleman during safety testing of the poliovirus vaccine in 1960
- Did not cause cytopathogenic effect (CPE) in cells
- Frequent contaminant of rhesus monkey kidney cell culture cells
- SV-40 is a well-characterized polyomavirus.
What are the characteristics of SV-40?
- Small (45 nm in diameter)
- Non-enveloped
- Icosahedral-shaped
- Three capsid proteins (VP1, VP2, VP3)
- dsDNA genome (5.2 kb in length)
Two sets of genes (expressed early and late)
Origin of replications (ORIs)
Promoters
Enhancer sequences
- Large and small T-antigens
Large T antigen interacts with tumor suppressor genes, inactivating cell cycle control
What is the SV-40 structure and Genome?
- Two other polyomaviruses found in humans
- Jamestown Canyon virus (JCV)
- BK virus (BKV)
- Both JCV and BKV cause tumors in animals and in about 5% of AIDS patients.
Discuss the Virus File 10-5 and the SV-40 Controversy
- Early lots of poliovirus vaccine were contaminated with SV-40.
- SV-40 can cause tumors in rodents.
- Vaccinees who received contaminated vaccines produced antibodies against SV-40.
- SV-40 DNA has been found in the DNA of tumor cells of rare cancers.
- Can SV-40 cause cancer?
- Some scientists are working on a vaccine against large T antigen.
What is Human Endogenous Retroviruses (HERVs)?
- 8% of the human genome consists of HERVs.
- Sequences containing gag, pol, env, and LTRs
- Most sequences are defective and incapable of producing gene products.
- Are HERVs involved in cancer? Autoimmunity? Neurological diseases?
What are Oncolytic Viruses?
Cancer Therapy: The last 150 years
- Surgery
- Radiation therapy
- Chemotherapy
- mustard gas
- aminopterin
Immunotherapy
Virotheraphy
What is involved in virotherapy in the 21st centure the oncolytic virus should?
The oncolytic virus should:
- not be a human pathogen. This reduces the chance of pre-existing immunity that would inhibit its therapeutic effectiveness.
- not cause toxicity or severe side effects to normal tissues and cells.
- be able to be genetically manipulated to facilitate the introduction of therapeutic or suicide genes and/or genes used to monitor its viral spread through the tumor or cancerous mass/tissues
- have a rapid life cycle such that it can replicate in cancer cells, lyse the cancer cells, and spread to other cancer cells quickly.
Virotherapy continued
- can be administered systemically (e.g., intravenous injection) to treat patients with metastatic disease.
- can eradicate the tumor and also establish anti-tumor immunity to contain metastases.
- does not enter the nucleus of its target cell or cannot recombine with the host cell genome to minimize the risk of virus–host genetic recombination events.
- naturally replicates in specifically in tumor tissue but not normal tissues or cells (e.g., Adenoviruses, mumps virus)should be susceptible to an antiviral drug.
- should be well characterized in terms of viral genome and protein function.
- the viral mechanism of oncolytic action and tumor specificity should be well-characterized.
What are the fundamental Concepts of Viruses and Cancer?
- Cancer develops when cells in part of the body begin to grow out of control
- Cancer is a multi-step process.
- 20% of all human cancers are associated with viruses
- Transformed cells undergo phenotypic, genetic, and metabolic changes in culture and in vivo.
- Retroviruses can cause cancer via the integration of a provirus into the host genome within or near cellular oncogenes.
- Human DNA tumor viruses include EBV, KSHV, HPV, and HBV.
- Animal DNA tumor viruses include adenovirus and SV-40.
- Current treatments for cancer include radiation, chemotherapy, immunotherapy.
- Virotherapy is an experimental form of cancer therapy in which viruses are used to target and destroy cancer cells.
