StAR-related lipid transfer domain protein 13 (STARD13) also known as deleted in liver cancer 2 protein (DLC-2) 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 STARD13 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...

 and a member of the DLC family of proteins.

Function and structure

STARD13 serves as a Rho GTPase-activating protein (GAP), a type of protein that regulates members of the Rho family of GTPases

Rho family of GTPases

The Rho family of GTPases is a family of small signaling G protein , and is a subfamily of the Ras superfamily. The members of the Rho GTPase family have been shown to regulate many aspects of intracellular actin dynamics, and are found in all eukaryotic organisms including yeasts and some plants...

. It selectively activates RhoA

RHOA

Ras homolog gene family, member A is a small GTPase protein known to regulate the actin cytoskeleton in the formation of stress fibers. In humans, it is encoded by the gene RHOA....

 and CDC42

CDC42

Cell division control protein 42 homolog also known as CDC42 is a protein involved in regulation of the cell cycle. In humans, CDC42 is encoded by the CDC42 gene.- Function :...

 and suppresses cell growth by inhibiting actin

Actin

Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...

 stress fiber assembly.

The protein consists of an N-terminal sterile alpha motif

Sterile alpha motif

Sterile alpha motif is a putative protein interaction module present in a wide variety of proteins involved in many biological processes. The SAM domain that spreads over around 70 residues is found in diverse eukaryotic organisms...

 (SAM) domain, a serine-rich domain, a RhoGAP domain

RhoGAP domain

RhoGAP domain is an evolutionary conserved protein domain ofGTPase activating proteins towards Rho/Rac/Cdc42-like small GTPases.-Human proteins containing this domain :ABR; ARHGAP1; ARHGAP10; ARHGAP11A; ARHGAP11B; ARHGAP12; ARHGAP15; ARHGAP17;...

 and at the C-terminus, a StAR-related lipid-transfer domain (START).

Tissue distribution and pathology

Although the protein is present in many different tissues in the body, deletion of the protein in mice has no adverse effects. However, loss of STARD13 may promote blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

 formation (angiogenesis

Angiogenesis

Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...

), especially by tumor cells. The promotion of angiogenesis with the loss of STARD13 occurs through the actions of RhoA.

The protein was identified in part through its differential expression in cancers. A low level of STARD13 was observed in less differentiated hepatocellular carcinoma

Hepatocellular carcinoma

Hepatocellular carcinoma is the most common type of liver cancer. Most cases of HCC are secondary to either a viral hepatitide infection or cirrhosis .Compared to other cancers, HCC is quite a rare tumor in the United States...

 tissue with higher RhoA expression. A small patient study finds that the absence of STARD13 in hepatocellular carcinomas correlates with higher levels of RhoA and a poorer prognosis

Prognosis

Prognosis is a medical term to describe the likely outcome of an illness.When applied to large statistical populations, prognostic estimates can be very accurate: for example the statement "45% of patients with severe septic shock will die within 28 days" can be made with some confidence, because...

than patients with carcinomas that were STARD13-positive.

Further reading