# DIRAS3

## Overview
DIRAS3, also known as ARHI or Noey2, is a gene that encodes the DIRAS family GTPase 3, a small GTPase protein with tumor suppressor functions. This protein is part of the Ras superfamily and is characterized by its ability to regulate key cellular processes, including cell proliferation, migration, and autophagy. Unlike the oncogenic H/N/K-RAS proteins, DIRAS3 contains a unique 34-amino acid N-terminal extension that is crucial for its tumor suppressive activity (Sutton2019DIRAS3). The protein is myristoylated, which aids in its localization to the plasma membrane, and it contains a CAAX-box domain at the C-terminus for membrane anchoring (Hutchins2024Intrinsically). DIRAS3 interacts with components of the RAS/MAPK signaling pathway, such as C-RAF, to inhibit downstream signaling and maintain cellular homeostasis (Klingauf2012The). Its expression is often downregulated in various cancers, making it a significant biomarker for cancer prognosis and a potential target for therapeutic interventions (Li2018The).

## Structure
DIRAS3, also known as ARHI, is a small GTPase with a molecular weight of 26 kDa. It shares 50%-60% homology with the oncogene H/N/K-RAS but is distinguished by a 34-amino acid N-terminal extension, which is crucial for its tumor suppressive functions (Sutton2019DIRAS3). This N-terminal extension is myristoylated, facilitating its localization to the plasma membrane (Hutchins2024Intrinsically). The protein also contains a CAAX-box membrane-anchoring domain at the C-terminus, essential for its membrane association and function (Sutton2019DIRAS3).

The secondary structure of DIRAS3 includes helical content, particularly in the N-terminal extension, which is referred to as DNTE. This region has approximately 14% helical content in solution, as determined by circular dichroism spectroscopy (Hutchins2024Intrinsically). The DNTE segment interacts extensively with lipid membranes through hydrophobic and basic residues, with specific residues like Leu 18, Leu 22, Ile 24, and Leu 25 deeply inserted into the bilayer (Hutchins2024Intrinsically).

DIRAS3 forms heteromers with RAS proteins, specifically binding to the A5 helical domain of H-RAS and K-RAS, which disrupts RAS clustering and inhibits downstream MAPK signaling (Sutton2019DIRAS3). This interaction suggests a quaternary structure involving complex formation with RAS proteins. The protein's ability to disrupt KRAS nanoclusters is also linked to its interactions with specific lipid species in the membrane (Hutchins2024Intrinsically).

## Function
DIRAS3, also known as ARHI or Noey2, is a tumor suppressor gene that encodes a Ras-like GTPase protein involved in several critical cellular processes. In healthy human cells, DIRAS3 plays a significant role in regulating the MAPK signaling pathway, particularly by interacting with C-RAF, a kinase upstream of MEK and ERK. This interaction is nucleotide-independent and crucial for inhibiting the phosphorylation of MEK and ERK, thereby restricting cell migration and proliferation (Klingauf2012The). DIRAS3's presence is essential for maintaining a non-migratory phenotype in non-cancerous tissues by downregulating ERK activity (Klingauf2012The).

DIRAS3 also interacts with the autophagy-specific class III PtdIns3K complex, particularly with the BECN1 protein, to regulate autophagy. This interaction is enhanced during nutrient deprivation, promoting autophagy and cell survival under stress conditions (Lu2014DIRAS3). DIRAS3 inhibits the interaction between BECN1 and BCL2, facilitating the transition of BECN1 from a homodimer to a monomer, which is necessary for autophagy activation (Lu2014DIRAS3). These functions highlight DIRAS3's role in maintaining cellular homeostasis and preventing excessive cell proliferation.

## Clinical Significance
DIRAS3, also known as ARHI, is a tumor suppressor gene whose altered expression is implicated in various cancers. In oligodendroglial tumors, particularly those with 1p loss, DIRAS3 is frequently inactivated through methylation, leading to reduced mRNA levels. This inactivation is associated with longer overall survival in patients, suggesting its potential as a prognostic marker (Riemenschneider2008Frequent). In ovarian, breast, pancreatic, and gastric cancers, DIRAS3 is often downregulated, correlating with increased tumor malignancy and poor prognosis (Klingauf2012The; Li2018The). The gene's downregulation is linked to mechanisms such as loss of heterozygosity, DNA methylation, and miRNA regulation (Li2018The; Sutton2019DIRAS3).

DIRAS3 interacts with the RAS/MAPK signaling pathway, inhibiting cell proliferation and migration. Its loss or reduced expression can lead to increased ERK activity, contributing to cancer progression (Klingauf2012The; Sutton2019DIRAS3). In gastric cancer, low DIRAS3 expression is associated with advanced cancer stages and metastasis, while higher expression correlates with better overall survival (Qiu2018Distinct). These findings highlight DIRAS3's role as a significant biomarker for cancer prognosis and a potential target for therapeutic interventions.

## Interactions
DIRAS3, also known as ARHI, is a tumor suppressor protein that interacts with several key proteins involved in the RAS/MAPK signaling pathway. DIRAS3 forms heteromers with H-RAS and K-RAS, inhibiting their function by disrupting RAS clustering and multimerization at the plasma membrane, which is crucial for RAS/MAPK signaling (Sutton2019DIRAS3). This interaction is mediated through the A5 helical domain of K-RAS and H-RAS, with DIRAS3 binding specifically to K-RAS but not to N-RAS or Rap1A (Sutton2019DIRAS3).

DIRAS3 also interacts with C-RAF, a component of the MAPK/ERK signaling pathway, in a nucleotide-independent manner. This interaction involves both the N-terminal and C-terminal regions of C-RAF, and DIRAS3 can simultaneously bind to C-RAF and H-RAS, facilitating the formation of a stable complex (Klingauf2012The; Baljuls2012The). DIRAS3's interaction with C-RAF inhibits C-RAF:B-RAF heterodimerization and reduces MEK and ERK phosphorylation, thereby downregulating the MEK-ERK signaling pathway (Klingauf2012The; Baljuls2016Stabilization). These interactions highlight DIRAS3's role in modulating key signaling pathways involved in cell proliferation and tumor suppression.


## References


[1. (Riemenschneider2008Frequent) Markus J. Riemenschneider, Julia Reifenberger, and Guido Reifenberger. Frequent biallelic inactivation and transcriptional silencing of the diras3 gene at 1p31 in oligodendroglial tumors with 1p loss. International Journal of Cancer, 122(11):2503–2510, February 2008. URL: http://dx.doi.org/10.1002/ijc.23409, doi:10.1002/ijc.23409. This article has 34 citations and is from a domain leading peer-reviewed journal.](https://doi.org/10.1002/ijc.23409)

[2. (Li2018The) Xueli Li, Shuiping Liu, Xiao Fang, Chao He, and Xiaotong Hu. The mechanisms of diras family members in role of tumor suppressor. Journal of Cellular Physiology, 234(5):5564–5577, October 2018. URL: http://dx.doi.org/10.1002/jcp.27376, doi:10.1002/jcp.27376. This article has 12 citations and is from a peer-reviewed journal.](https://doi.org/10.1002/jcp.27376)

[3. (Hutchins2024Intrinsically) Chase M. Hutchins and Alemayehu A. Gorfe. Intrinsically disordered membrane anchors of rheb, rhoa, and diras3 small gtpases: molecular dynamics, membrane organization, and interactions. The Journal of Physical Chemistry B, 128(27):6518–6528, June 2024. URL: http://dx.doi.org/10.1021/acs.jpcb.4c01876, doi:10.1021/acs.jpcb.4c01876. This article has 0 citations.](https://doi.org/10.1021/acs.jpcb.4c01876)

[4. (Klingauf2012The) Mirko Klingauf, Matthias Beck, Ulrich Berge, Yagmur Turgay, Stephan Heinzer, Peter Horvath, and Ruth Kroschewski. The tumour suppressor diras3 interacts with c‐raf and downregulates mek activity to restrict cell migration. Biology of the Cell, 105(2):91–107, December 2012. URL: http://dx.doi.org/10.1111/boc.201200030, doi:10.1111/boc.201200030. This article has 17 citations and is from a peer-reviewed journal.](https://doi.org/10.1111/boc.201200030)

[5. (Qiu2018Distinct) Jingping Qiu, Xiaoting Li, Yingjian He, Dan Sun, Wenhui Li, and Yan Xin. Distinct subgroup of the ras family member 3 (diras3) expression impairs metastasis and induces autophagy of gastric cancer cells in mice. Journal of Cancer Research and Clinical Oncology, 144(10):1869–1886, July 2018. URL: http://dx.doi.org/10.1007/s00432-018-2708-3, doi:10.1007/s00432-018-2708-3. This article has 9 citations and is from a peer-reviewed journal.](https://doi.org/10.1007/s00432-018-2708-3)

[6. (Baljuls2016Stabilization) Angela Baljuls, Maciej Dobrzyński, Jens Rauch, Nora Rauch, and Walter Kolch. Stabilization of c-raf:ksr1 complex by diras3 reduces availability of c-raf for dimerization with b-raf. Cellular Signalling, 28(10):1451–1462, October 2016. URL: http://dx.doi.org/10.1016/j.cellsig.2016.06.019, doi:10.1016/j.cellsig.2016.06.019. This article has 6 citations and is from a peer-reviewed journal.](https://doi.org/10.1016/j.cellsig.2016.06.019)

[7. (Lu2014DIRAS3) Zhen Lu, Maria T Baquero, Hailing Yang, Maojie Yang, Albert S Reger, Choel Kim, Douglas A Levine, Charlotte H Clarke, Warren S-L Liao, and Robert C Bast Jr. Diras3 regulates the autophagosome initiation complex in dormant ovarian cancer cells. Autophagy, 10(6):1071–1092, April 2014. URL: http://dx.doi.org/10.4161/auto.28577, doi:10.4161/auto.28577. This article has 59 citations and is from a domain leading peer-reviewed journal.](https://doi.org/10.4161/auto.28577)

[8. (Baljuls2012The) Angela Baljuls, Matthias Beck, Ayla Oenel, Armin Robubi, Ruth Kroschewski, Mirko Hekman, Thomas Rudel, and Ulf R. Rapp. The tumor suppressor diras3 forms a complex with h-ras and c-raf proteins and regulates localization, dimerization, and kinase activity of c-raf. Journal of Biological Chemistry, 287(27):23128–23140, June 2012. URL: http://dx.doi.org/10.1074/jbc.M112.343780, doi:10.1074/jbc.m112.343780. This article has 15 citations and is from a domain leading peer-reviewed journal.](https://doi.org/10.1074/jbc.M112.343780)

[9. (Sutton2019DIRAS3) Margie N. Sutton, Zhen Lu, Yao-Cheng Li, Yong Zhou, Tao Huang, Albert S. Reger, Amy M. Hurwitz, Timothy Palzkill, Craig Logsdon, Xiaowen Liang, Joe W. Gray, Xiaolin Nan, John Hancock, Geoffrey M. Wahl, and Robert C. Bast. Diras3 (arhi) blocks ras/mapk signaling by binding directly to ras and disrupting ras clusters. Cell Reports, 29(11):3448-3459.e6, December 2019. URL: http://dx.doi.org/10.1016/j.celrep.2019.11.045, doi:10.1016/j.celrep.2019.11.045. This article has 49 citations and is from a highest quality peer-reviewed journal.](https://doi.org/10.1016/j.celrep.2019.11.045)