Rapamycin-insensitive companion of mammalian target of rapamycin (RICTOR) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

that in humans is encoded by the ''RICTOR''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. RICTOR and

mTOR The mammalian target of rapamycin (mTOR), also referred to as the mechanistic target of rapamycin, and sometimes called FK506-binding protein 12-rapamycin-associated protein 1 (FRAP1), is a kinase that in humans is encoded by the ''MTOR'' gene. ...

are components of a protein complex that integrates nutrient- and growth factor-derived signals to regulate cell growth.

Structure

The gene RICTOR is located on

chromosome 5 Chromosome 5 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 5 spans about 181 million base pairs (the building blocks of DNA) and represents almost 6% of the total DNA in cells. C ...

at 5p13.1 with a sequence length of 5440 bp, oriented on the minus strand. The translated RICTOR protein contains 1709 amino acids and is present in the cytosol. RICTOR contains few conserved regions and function domains of RICTOR have yet to be observed. However, using

liquid chromatography In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...

tandem mass spectrometry Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more mass analyzers are coupled together using an additional reaction step to increase their abilities to analyse chemical samples. A com ...

analysis, 21 phosphorylation sites were identified on RICTOR. Of these sites, T1135 has been shown to undergo growth factor-responsive phosphorylation via

S6K1 Ribosomal protein S6 kinase beta-1 (S6K1), also known as p70S6 kinase (p70S6K, p70-S6K), is an enzyme (specifically, a protein kinase) that in humans is encoded by the ''RPS6KB1'' gene. It is a serine/threonine kinase that acts downstream of PIP3 ...

Function

RICTOR is a subunit of the mammalian target of rapamycin complex 2 ( mTORC2) which contains

, GβL, RICTOR (this protein) and mSIN1. The mammalian target of rapamycin (

) is a highly conserved Ser/Thr kinase that regulates cell growth and proliferation.

may exist as mTOR complex 1 (

mTORC1 mTORC1, also known as mammalian target of rapamycin complex 1 or mechanistic target of rapamycin complex 1, is a protein complex that functions as a nutrient/energy/redox sensor and controls protein synthesis. mTOR Complex 1 (mTORC1) is compo ...

) or mTOR complex 2 ( mTORC2). RICTOR is a key component of mTORC2, which, unlike mTORC1, is not directly inhibited by

rapamycin Sirolimus, also known as rapamycin and sold under the brand name Rapamune among others, is a macrolide compound that is used to coat coronary stents, prevent organ transplant rejection, treat a rare lung disease called lymphangioleiomyomatosi ...

. mTORC2, and RICTOR, specifically, has been shown to phosphorylate

Akt Protein kinase B (PKB), also known as Akt, is the collective name of a set of three serine/threonine-specific protein kinases that play key roles in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, tran ...

/ protein kinase B (PKB) on SER473. This phosphorylation activates

/ PKB, where deregulation of

/ PKB has been implicated in cancer and diabetes. RICTOR and mTORC2 have been shown to play an essential role in embryonic growth and development, perhaps due to the control that mTORC2 exerts on

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ov ...

cytoskeleton organization. RICTOR action

Regulation

FoxO FOX (forkhead box) proteins are a family of transcription factors that play important roles in regulating the expression of genes involved in cell growth, proliferation, differentiation, and longevity. Many FOX proteins are important to embryonic ...

transcription factors can activate expression of RICTOR. FoxO has been shown to inhibit mTORC1, while activating Akt through RICTOR elevation.

Degradation

Perifosine Perifosine (also KRX-0401) is a former drug candidate that was under development for a variety of cancer indications. It is an alkyl- phospholipid structurally related to miltefosine. Perifosine interrupts the PI3K/AKT/mTOR pathway by acting as a ...

has been shown to interfere with mTOR activity by degrading its components, such as RICTOR.

Interactions

RICTOR has been shown to

interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with and play a role in: RICTOR interactions network

Clinical relevance

Diseases associated with mutation in the RICTOR gene include foramen magnum meningioma and

syringomyelia Syringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. Often, syringomyelia is used as a generic term before an etiology is determined. This cyst, called a syrinx, can expand and elongate o ...

. Akt/PMB activation is also involved in

glucose metabolism Carbohydrate metabolism is the whole of the biochemical processes responsible for the metabolic formation, breakdown, and interconversion of carbohydrates in living organisms. Carbohydrates are central to many essential metabolic pathways. Pla ...

and activation of Akt by RICTOR has been shown to mediate glucose and lipid metabolism. Therefore, the influence of RICTOR and mTORC2 on Akt signaling has been associated with insulin resistance and

type 2 diabetes Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urinatio ...

Cancer

Akt/PMB activation leads to proliferation and survival, therefore over-activation of the Akt/PMB pathway by mTORC2 (including RICTOR) is implicated in cancerous growth. In human

colorectal carcinoma Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine). Signs and symptoms may include blood in the stool, a change in bowel ...

, RICTOR has been shown to association with

FBXW7 F-box/WD repeat-containing protein 7 is a protein that in humans is encoded by the ''FBXW7'' gene. Function This gene encodes a member of the F-box protein family which is characterized by an approximately 40 amino acid motif, the F-box. The F ...

(outside of mTORC2) to mediate the

ubiquitination Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...

of growth-promoting factors

cyclin E Cyclin E is a member of the cyclin family. Cyclin E binds to G1 phase Cdk2, which is required for the transition from G1 to S phase of the cell cycle that determines initiation of DNA duplication. The Cyclin E/CDK2 complex phosphorylates p27K ...

and

c-Myc ''Myc'' is a family of regulator genes and proto-oncogenes that code for transcription factors. The ''Myc'' family consists of three related human genes: ''c-myc'' ( MYC), ''l-myc'' ( MYCL), and ''n-myc'' ( MYCN). ''c-myc'' (also sometimes re ...

. Furthermore, elevated growth factor signaling may suppress the ubiquitinating action of RICTOR-FBXW7, resulting in accumulation of

and

and subsequent progression through the cell cycle. In

glioblastoma Glioblastoma, previously known as glioblastoma multiforme (GBM), is one of the most aggressive types of cancer that begin within the brain. Initially, signs and symptoms of glioblastoma are nonspecific. They may include headaches, personality ...

(GBM), RICTOR(along with EGFR) may serve as an effective therapeutic target for silencing RNA, leading to decreased cell proliferation. Co-silencing of RICTOR and EGFR lead to increased sensitivity to alkaloids and alkylating agents. For one particular PTEN-mutant cell line, co-silencing resulted in tumor eradication. RICTOR has been shown to be significantly overexpressed in well-differentiated

leiomyosarcoma Leiomyosarcoma is a malignant (cancerous) smooth muscle tumor. A benign tumor originating from the same tissue is termed leiomyoma. While leiomyosarcomas are not thought to arise from leiomyomas, some leiomyoma variants' classification is evolv ...

s. Due to the influence of RICTOR on

polymerization, RICTOR could play a role in allowing transcription and subsequent differentiation in these muscle cells. mTOR subunits RICTOR and RAPTOR both showed increased expression, which increased with

pituitary adenoma Pituitary adenomas are tumors that occur in the pituitary gland. Most pituitary tumors are benign, approximately 35% are invasive and just 0.1% to 0.2% are carcinomas.mTOR The mammalian target of rapamycin (mTOR), also referred to as the mechanistic target of rapamycin, and sometimes called FK506-binding protein 12-rapamycin-associated protein 1 (FRAP1), is a kinase that in humans is encoded by the ''MTOR'' gene. ...

RPTOR Regulatory-associated protein of mTOR also known as raptor or KIAA1303 is an adapter protein that is encoded in humans by the ''RPTOR'' gene. Two mRNAs from the gene have been identified that encode proteins of 1335 (isoform 1) and 1177 (isofor ...

and RICTOR were significantly correlated with the growth and invasion of pituitary adenomas and may have an important predictive and prognostic value in such patients.