A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. Many retroviruses cause serious diseases in humans, other mammals, and birds.
Papillomaviridae is a family of non-enveloped DNA viruses whose members are known as papillomaviruses. Several hundred species of papillomaviruses, traditionally referred to as "types", have been identified infecting all carefully inspected mammals, but also other vertebrates such as birds, snakes, turtles and fish. Infection by most papillomavirus types, depending on the type, is either asymptomatic or causes small benign tumors, known as papillomas or warts. Papillomas caused by some types, however, such as human papillomaviruses 16 and 18, carry a risk of becoming cancerous.
Polyomaviridae is a family of viruses whose natural hosts are primarily mammals and birds. As of 2020, there are six recognized genera and 117 species, five of which are unassigned to a genus. 14 species are known to infect humans, while others, such as Simian Virus 40, have been identified in humans to a lesser extent. Most of these viruses are very common and typically asymptomatic in most human populations studied. BK virus is associated with nephropathy in renal transplant and non-renal solid organ transplant patients, JC virus with progressive multifocal leukoencephalopathy, and Merkel cell virus with Merkel cell cancer.
An oncovirus or oncogenic virus is a virus that can cause cancer. This term originated from studies of acutely transforming retroviruses in the 1950–60s, when the term "oncornaviruses" was used to denote their RNA virus origin. With the letters "RNA" removed, it now refers to any virus with a DNA or RNA genome causing cancer and is synonymous with "tumor virus" or "cancer virus". The vast majority of human and animal viruses do not cause cancer, probably because of longstanding co-evolution between the virus and its host. Oncoviruses have been important not only in epidemiology, but also in investigations of cell cycle control mechanisms such as the retinoblastoma protein.
Gammaretrovirus is a genus in the Retroviridae family. Example species are the murine leukemia virus and the feline leukemia virus. They cause various sarcomas, leukemias and immune deficiencies in mammals, reptiles and birds.
Endogenous retroviruses (ERVs) are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. They are abundant in the genomes of jawed vertebrates, and they comprise up to 5–8% of the human genome.
Jaagsiekte sheep retrovirus (JSRV) is a betaretrovirus which is the causative agent of a contagious lung cancer in sheep, called ovine pulmonary adenocarcinoma.
The murine leukemia viruses are retroviruses named for their ability to cause cancer in murine (mouse) hosts. Some MLVs may infect other vertebrates. MLVs include both exogenous and endogenous viruses. Replicating MLVs have a positive sense, single-stranded RNA (ssRNA) genome that replicates through a DNA intermediate via the process of reverse transcription.
Env is a viral gene that encodes the protein forming the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane.
Koala retrovirus (KoRV) is a retrovirus that is present in many populations of koalas. It has been implicated as the agent of koala immune deficiency syndrome (KIDS), an AIDS-like immunodeficiency that leaves infected koalas more susceptible to infectious disease and cancers. The virus is thought to be a recently introduced exogenous virus that is also integrating into the koala genome. Thus the virus can transmit both horizontally and vertically. The horizontal modes of transmission are not well defined but are thought to require close contact.
Retroviral matrix proteins are components of envelope-associated capsids of retroviruses. These proteins line the inner surface of viral envelopes and are associated with viral membranes.
Mason-Pfizer monkey virus (M-PMV), formerly Simian retrovirus (SRV), is a species of retroviruses that usually infect and cause a fatal immune deficiency in Asian macaques. The ssRNA virus appears sporadically in mammary carcinoma of captive macaques at breeding facilities which expected as the natural host, but the prevalence of this virus in feral macaques remains unknown. M-PMV was transmitted naturally by virus-containing body fluids, via biting, scratching, grooming, and fighting. Cross contaminated instruments or equipment (fomite) can also spread this virus among animals.
Murine polyomavirus is an unenveloped double-stranded DNA virus of the polyomavirus family. The first member of the family discovered, it was originally identified by accident in the 1950s. A component of mouse leukemia extract capable of causing tumors, particularly in the parotid gland, in newborn mice was reported by Ludwik Gross in 1953 and identified as a virus by Sarah Stewart and Bernice Eddy at the National Cancer Institute, after whom it was once called "SE polyoma". Stewart and Eddy would go on to study related polyomaviruses such as SV40 that infect primates, including humans. These discoveries were widely reported at the time and formed the early stages of understanding of oncoviruses.
Human mammary tumor virus (HMTV) is a B-type retrovirus that is closely related to the mouse mammary tumor virus (MMTV). The existence of this virus was suspected for decades but nucleotide sequences identifying a unique virus in human breast cancer tumors were not confirmed until 2001. Viral particles were isolated several years later. Evidence for a role of HTMV/MMTV in human breast cancer has recently been reviewed.
Breast cancer metastatic mouse models are experimental approaches in which mice are genetically manipulated to develop a mammary tumor leading to distant focal lesions of mammary epithelium created by metastasis. Mammary cancers in mice can be caused by genetic mutations that have been identified in human cancer. This means models can be generated based upon molecular lesions consistent with the human disease.
Janet S Butel is the Chairman and Distinguished Service Professor in the molecular virology and microbiology department at Baylor College of Medicine. Her area of expertise is on polyomavirus pathogenesis of infections and disease. She has more than 120 publications on PubMed. She also has 6 publications in Nature, which is considered one of the most prestigious science journals. She is a member of 9 different organizations and has 13 honors and awards.
Human endogenous retrovirus K (HERV-K) or Human teratocarcinoma-derived virus (HDTV) is a family of human endogenous retroviruses associated with malignant tumors of the testes. Phylogenetically, the HERV-K group belongs to the ERV2 or Class II or Betaretrovirus-like supergroup. Over the past several years, it has been found that this group of ERVs play an important role in embryogenesis, but their expression is silenced in most cell types in healthy adults. The HERV-K family, and particularly its subgroup HML-2, is the youngest and most transcriptionally active group and hence, it is the best studied among other ERVs. Reactivation of it or anomalous expression of HML-2 in adult tissues has been associated with various types of cancer and with neurodegenerative diseases such as amytrophic lateral sclerosis (ALS). Endogenous retrovirus K (HERV-K) is related to mammary tumor virus in mice. It exists in the human and cercopithecoid genomes. Human genome contains hundreds of copies of HERV-K and many of them possess complete open reading frames (ORFs) that are transcribed and translated, especially in early embryogenesis and in malignancies. One notable location of HERV-K is the C4 gene of RCCX module. HERV-K is also found in apes and Old World monkeys. It is uncertain how long ago in primate evolution the full-length HERV-K proviruses which are in the human genome today were created.
Human Endogenous Retrovirus-W (HERV-W) is a family of Human Endogenous Retroviruses, or HERVs.
The small tumor antigen is a protein encoded in the genomes of polyomaviruses, which are small double-stranded DNA viruses. STag is expressed early in the infectious cycle and is usually not essential for viral proliferation, though in most polyomaviruses it does improve replication efficiency. The STag protein is expressed from a gene that overlaps the large tumor antigen (LTag) such that the two proteins share an N-terminal DnaJ-like domain but have distinct C-terminal regions. STag is known to interact with host cell proteins, most notably protein phosphatase 2A (PP2A), and may activate the expression of cellular proteins associated with the cell cycle transition to S phase. In some polyomaviruses - such as the well-studied SV40, which natively infects monkeys - STag is unable to induce neoplastic transformation in the host cell on its own, but its presence may increase the transforming efficiency of LTag. In other polyomaviruses, such as Merkel cell polyomavirus, which causes Merkel cell carcinoma in humans, STag appears to be important for replication and to be an oncoprotein in its own right.
The middle tumor antigen is a protein encoded in the genomes of some polyomaviruses, which are small double-stranded DNA viruses. MTag is expressed early in the infectious cycle along with two other related proteins, the small tumor antigen and large tumor antigen. MTag occurs only in a few known polyomaviruses, while STag and LTag are universal - it was first identified in mouse polyomavirus (MPyV), the first polyomavirus discovered, and also occurs in hamster polyomavirus. In MPyV, MTag is an efficient oncoprotein that can be sufficient to induce neoplastic transformation in some cells.
