Viral transformation most commonly refers to the virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

-induced malignant transformation of an animal cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 in a body or cell culture

Cell culture

Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

. In molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

, the term may also refer to the transfection

Transfection

Transfection is the process of deliberately introducing nucleic acids into cells. The term is used notably for non-viral methods in eukaryotic cells...

 of DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 into a host cell using a viral vector

Viral vector

Viral vectors are a tool commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism or in cell culture . Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect...

.

Virus-induced malignant transformation

Viral transformation can impose characteristically determinable features upon a cell. Typical phenotypic

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

 changes include high saturation density, anchorage-independent growth, loss of contact inhibition, loss of orientated growth, immortalisation, disruption of the cell's cytoskeleton

Cytoskeleton

The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...

.

Epidemiological studies suggest that malignant transformation of cells by viruses occurs via multiple steps. This involves initiation, promotion and progression events. Viruses act along with other factors to transform cells. The persistence of at least part of the viral genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 within the cell is required for cell transformation. This is accompanied by the continual expression from a number of viral gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s. These genes interfere with a cell's signaling pathway

Signal transduction

Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

 causing the observed phenotypic changes of the cell. The end result is a transformed cell showing increased cell division, which is favorable to the virus.

Transformation using viral vectors

The term transformation

Transformation (genetics)

In molecular biology transformation is the genetic alteration of a cell resulting from the direct uptake, incorporation and expression of exogenous genetic material from its surroundings and taken up through the cell membrane. Transformation occurs naturally in some species of bacteria, but it can...

 is also used for the introduction of foreign DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 into cells, which can be achieved using a viral vector

Viral vector

Viral vectors are a tool commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism or in cell culture . Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect...

 to transfer the DNA. This process is also referred to as transfection

Transfection

Transfection is the process of deliberately introducing nucleic acids into cells. The term is used notably for non-viral methods in eukaryotic cells...

 or transduction

Transduction (genetics)

Transduction is the process by which DNA is transferred from one bacterium to another by a virus. It also refers to the process whereby foreign DNA is introduced into another cell via a viral vector. Transduction does not require cell-to-cell contact , and it is DNAase resistant...

, respectively.