TGF alpha
Transforming growth factor alpha (TGF-) is a protein that in humans is encoded by the TGFA gene. As a member of the epidermal growth factor (EGF) family, TGF- is a mitogenic polypeptide. The protein becomes activated when binding to receptors capable of protein kinase activity for cellular signaling.
TGF- is a transforming growth factor that is a ligand for the epidermal growth factor receptor, which activates a signaling pathway for cell proliferation, differentiation and development. This protein may act as either a transmembrane-bound ligand or a soluble ligand. This gene has been associated with many types of cancers, and it may also be involved in some cases of cleft lip/palate.

# Synthesis
TGF- is synthesized internally as part of a 160 (human) or 159 (rat) amino acid transmembrane precursor. The precursor is composed of an extracellular domain containing a hydrophobic transmembrane domain, 50 amino acids of TGF-, and a 35-residue-long cytoplasmic domain. In its smallest form TGF- has six cysteines linked together via three disulfide bridges.  Collectively all members of the EGF/TGF- family share this structure.  The protein, however, is not directly related to TGF-. 
In the stomach, TGF- is manufactured within the normal gastric mucosa. TGF- has been shown to inhibit gastric acid secretion.
Limited success has resulted from attempts to synthesize of a reductant molecule to TGF- that displays a similar biological profile.

## Synthesis in the stomach
In the stomach, TGF- is manufactured within the normal gastric mucosa. TGF- has been shown to inhibit gastric acid secretion.

# Function
TGF- can be produced in macrophages, brain cells, and keratinocytes.  TGF- induces epithelial development.  Considering that TGF- is a member of the EGF family, the biological actions of TGF- and EGF are similar.  For instance, TGF- and EGF bind to the same receptor.  When TGF- binds to EGFR it can initiate multiple cell proliferation events. Cell proliferation events that involve TGF- bound to EGFR include wound healing and embryogenesis.  TGF- is also involved in tumerogenesis and believed to promote angiogenesis.
TGF has also been shown to stimulate neural cell proliferation in the adult injured brain.

# Receptor
A 170-kDa glycosylated protein known as the EGF receptor binds to TGF- allowing the polypeptide to function in various signaling pathways. The EGF receptor is characterized by having an extracellular domain that has numerous amino acid motifs. EGFR is essential for a single transmembrane domain, an intracellular domain (containing tyrosine kinase activity), and ligand recognition. As a membrane anchored-growth factor, TGF- can be cleaved from an integral membrane glycoprotein via a protease.  Soluble forms of TGF- resulting from the cleavage have the capacity to activate EGFR. EGFR can be activated from a membrane-anchored growth factor as well.
When TGF- binds to EGFR it dimerizes triggering phosphorylation of a protein-tyrosine kinase.  The activity of protein-tyrosine kinase causes an autophosphorylation to occur among several tyrosine residues within EGFR, influencing activation and signaling of other proteins that interact in many signal transduction pathways.

# Animal studies
In an animal model of Parkinson's disease where dopaminergic neurons have been damaged by 6-hydroxydopamine, infusion of TGF- into the brain caused an increase in the number of neuronal precursor cells. However TGF- treatment did not result in neurogenesis dopaminergic neurons.

# Human studies

## Neuroendocrine system
The EGF/TGF- family has been shown to regulate luteinizing hormone-releasing hormone (LHRH) through a glial-neuronal interactive process.  Produced in hypothalamic astrocytes, TGF- indirectly stimulates LHRH release through various intermediates.  As a result, TGF- is a physiological component essential to the initiation process of female puberty.

## Suprachiasmatic nucleus
TGF- has also been observed to be highly expressed in the suprachiasmatic nucleus (SCN) (5).  This finding suggests a role for EGFR signaling in the regulation of CLOCK and circadian rhythms within the SCN.  Similar studies have shown that when injected into the third ventricle TGF- can suppress circadian locomotor behavior along with drinking or eating activities.

## Tumors
Its potential use as a prognostic biomarker in various tumors, like gastric carcinoma. or melanoma has been suggested. Elevated TGF- is associated with Menetrier's disease, a precancerous condition of the stomach.

# Interactions
TGF alpha has been shown to interact with GORASP1 and GORASP2.