FBJ murine osteosarcoma viral oncogene homolog B also known as FOSB (in humans) or FosB (in other species) is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that, in humans, is encoded by the FOSB 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...

.

The Fos gene family consists of 4 members: FOS

C-Fos

In the field of molecular biology and Genetics, c-Fos is a protein encoded by the FOS gene.-Structure and function:c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors. c-Fos has a leucine-zipper DNA binding domain, and a transactivation domain at...

, FOSB, FOSL1

FOSL1

Fos-related antigen 1 is a protein that in humans is encoded by the FOSL1 gene.-Interactions:FOSL1 has been shown to interact with USF1 and C-jun....

, and FOSL2

FOSL2

Fos-related antigen 2 is a protein that in humans is encoded by the FOSL2 gene....

. These genes encode leucine zipper

Leucine zipper

A leucine zipper, aka leucine scissors, is a common three-dimensional structural motif in proteins. These motifs are usually found as part of a DNA-binding domain in various transcription factors, and are therefore involved in regulating gene expression...

 proteins that can dimerize with proteins of the JUN

C-jun

c-Jun is the name of a gene and protein that, in combination with c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only later rediscovered as the product of the c-jun gene. It is activated through double phosphorylation by the...

 family, thereby forming the transcription factor complex AP-1

AP-1 (transcription factor)

In the field of molecular biology, the activator protein 1 is a transcription factor which is a heterodimeric protein composed of proteins belonging to the c-Fos, c-Jun, ATF and JDP families. It regulates gene expression in response to a variety of stimuli, including cytokines, growth factors,...

. As such, the FOS proteins have been implicated as regulators of cell proliferation, differentiation, and transformation.

Delta FosB

Delta FosB is a truncated splice variant of FosB. Delta FosB has been implicated in the development of drug addiction and control of the reward system

Reward system

In neuroscience, the reward system is a collection of brain structures which attempts to regulate and control behavior by inducing pleasurable effects...

 in the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

, and is linked to changes in a number of other gene products such as CREB

CREB

CREB is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements , thereby increasing or decreasing the transcription of the downstream genes....

 and sirtuin

Sirtuin

Sirtuin or Sir2 proteins are a class of proteins that possess either histone deacetylase or mono-ribosyltransferase activity. Sirtuins regulate important biological pathways in bacteria, archaea and eukaryotes...

s. Delta FosB also regulates the commitment of mesenchymal precursor cells to the adipocyte

Adipocyte

However, in some reports and textbooks, the number of fat cell increased in childhood and adolescence. The total number is constant in both obese and lean adult...

 or osteoblast

Osteoblast

Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...

 lineage.

Role in cocaine use

Delta FosB levels have been found to increase upon the use of cocaine. Each subsequent dose of cocaine will continue to increase the levels of Delta FosB with no ceiling of tolerance. Increasing the levels of Delta FosB has led to increases in brain-derived neurotrophic factor (BDNF) levels, which in turn will increase the number of dendritic branches and spines present on neurons involved with the nucleus accumbens

Nucleus accumbens

The nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...

 and prefrontal cortex

Prefrontal cortex

The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...

 areas of the brain. This change can be identified rather quickly, and may be sustained weeks after the last dose of the drug. This consequence of cocaine use may attribute to the idea of sensitization

Sensitization

Sensitization is an example of non-associative learning in which the progressive amplification of a response follows repeated administrations of a stimulus. An everyday example of this mechanism is the repeated tonic stimulation of peripheral nerves that will occur if a person rubs his arm...

presented with the drug.

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