<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">hras</th>
</tr>
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<td class="label">Symbol</td>
<td><strong>HRAS</strong></td>
</tr>
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<td class="label">Full Name</td>
<td>hras</td>
</tr>
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<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=HRAS" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">167 edges</a></td>
</tr>
</table>
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">hras</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>HRAS</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>hras</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=HRAS" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">167 edges</a></td>
</tr>
</table>
HRAS (Harvey Rat Sarcoma Viral Oncogene Homolog) is a prototype member of the Ras family of small GTPases that functions as a molecular switch in intracellular signaling pathways. The HRAS gene encodes a 188-amino acid protein that cycles between an active GTP-bound state and an inactive GDP-bound state, controlling a wide range of cellular processes including proliferation, differentiation, survival, and synaptic plasticity. Originally identified as the transforming oncogene of the Harvey murine sarcoma virus, HRAS has since been recognized as a critical regulator of neuronal function in the central nervous system. The gene is located on chromosome 11p15.5 (NCBI Gene ID: 3265, Ensembl: ENSG00000174775, UniProt: P01112) and is expressed throughout the brain, with particularly high levels in regions critical for learning and memory, motor control, and executive function. Germline HRAS mutations cause Costello syndrome, a developmental disorder characterized by intellectual disability, distinctive facial features, and increased tumor risk. Somatic HRAS mutations are among the most common oncogenic alterations in human cancer. In the nervous system, HRAS plays essential roles in neuronal development, synaptic plasticity, learning and memory, and the response to neuronal injury. Dysregulated HRAS signaling has been implicated in neurodegenerative diseases including Alzheimer's disease and Parkinson's disease, as well as in neurodevelopmental disorders and excitotoxicity. This comprehensive review covers HRAS gene structure, protein function, neuronal expression patterns, signaling pathways, disease associations, and therapeutic implications for neurodegenerative conditions. [@bos1989][@barsagi2000]
The HRAS gene spans approximately 6.5 kb on chromosome 11p15.5 and consists of 6 exons encoding a 188-amino acid protein. The genomic region surrounding HRAS is subject to imprinting, with monoallelic expression from the paternal allele in some tissues. The HRAS promoter contains binding sites for multiple transcription factors including SP1, AP-1, and NF-κB, enabling responsive regulation in different cellular contexts. The gene is highly conserved across mammalian species, reflecting its fundamental cellular functions. Alternative splicing generates multiple transcript variants, though the functional significance of these variants in the nervous system is not fully characterized. The HRAS locus is part of a cluster of Ras family genes on chromosome 11p15.5, which also includes the pseudogenes HRAS1 and HRAS1P. Mutations in HRAS are among the most common activating mutations in human cancer, particularly in bladder cancer, thyroid cancer, and certain types of leukemia. The germline mutations that cause Costello syndrome are distinct from the somatic mutations found in cancers, with different functional consequences and clinical implications. Understanding the genomic organization and regulation of HRAS provides insight into its tissue-specific expression and disease associations. [@gilsbach2005]
HRAS is widely expressed throughout the central nervous system, with regional specificity that reflects its functional roles in different neural circuits. In the hippocampus, HRAS is expressed at high levels in CA1-CA3 pyramidal neurons and in dentate gyrus granule cells, regions critical for learning and memory formation. The cerebral cortex shows HRAS expression in pyramidal neurons across all layers, with particularly high levels in layer 5 neurons that project to subcortical structures. The cerebellum expresses HRAS prominently in Purkinje cells, the sole output neurons of the cerebellar cortex, as well as in granule cells and deep cerebellar nuclei neurons. In the basal ganglia, HRAS is expressed in medium spiny neurons of the striatum and in dopaminergic neurons of the substantia nigra pars compacta. The amygdala, thalamus, and hypothalamus also show significant HRAS expression, reflecting roles in emotional processing, sensory relay, and homeostatic regulation. Within neurons, HRAS is localized to both the soma and dendritic compartments, with particular enrichment at synapses where it participates in activity-dependent signaling. Astrocytes and microglia also express HRAS, where it contributes to glial function and neuroinflammatory responses. The widespread brain expression of HRAS underscores its importance in diverse neuronal functions. [@li2006]
The HRAS protein is a 188-amino acid, 21 kDa GTPase that functions as a molecular switch in intracellular signaling. Like all Ras proteins, HRAS possesses intrinsic GTPase activity that hydrolyzes GTP to GDP, returning the protein to its inactive state. However, the intrinsic GTPase activity of HRAS is slow, and the protein requires interaction with GTPase-activating proteins (GAPs) to accelerate hydrolysis. GAPs such as p120GAP and NF1 in neurons dramatically increase the rate of GTP hydrolysis, ensuring tight regulation of HRAS signaling. Conversely, guanine nucleotide exchange factors (GEFs) such as SOS1 and RASGRP1 promote the exchange of GDP for GTP, activating HRAS. The cycle of activation and inactivation is further regulated by GDP dissociation inhibitors (GDIs) that sequester inactive HRAS in the cytosol. The GTP-bound form of HRAS adopts a conformation that enables interaction with downstream effectors, while the GDP-bound form is unable to bind these targets. Post-translational modifications, particularly prenylation of the C-terminal CAAX motif (Cys-Val-Ile-Met), are required for membrane localization and function. Additional modifications including phosphorylation and ubiquitination further regulate HRAS activity and stability. The balance between GEFs, GAPs, and GDIs determines the active HRAS-GTP pool in cells, providing precise temporal and spatial control of signaling. [@barsagi2000]
HRAS activates multiple downstream signaling cascades that influence neuronal function. The best-characterized pathway is the MAPK/ERK cascade, where HRAS-GTP recruits and activates RAF kinases (A-RAF, B-RAF, C-RAF), which then phosphorylate and activate MEK1/2, which in turn phosphorylate and activate ERK1/2. Activated ERK phosphorylates numerous substrates including transcription factors (ELK-1, c-Fos, c-Myc), cytoskeletal proteins, and other signaling molecules, leading to changes in gene expression and cellular behavior. HRAS also activates the PI3K/AKT pathway, which promotes cell survival through phosphorylation and inhibition of pro-apoptotic proteins. The RAL pathway, mediated by RALGEFs activated by HRAS-GTP, regulates vesicle trafficking and cytoskeletal dynamics. Additionally, HRAS can activate PLCε, leading to calcium signaling and PKC activation. In neurons, these pathways mediate the effects of HRAS on synaptic plasticity, learning and memory, neuronal development, and the response to injury. The specific biological outcomes depend on the cell type, developmental stage, and input specificity of signaling. Pathway crosstalk and feedback loops ensure appropriate responses to different stimuli. The diversity of downstream effectors allows HRAS to influence many aspects of neuronal function. [@downward2003]
HRAS plays critical roles in neuronal development, influencing proliferation, differentiation, migration, and morphogenesis. During development, HRAS-mediated MAPK/ERK signaling promotes the transition from neural progenitor proliferation to neuronal differentiation. This pathway is activated by growth factors including BDNF, NGF, and FGF, which signal through receptor tyrosine kinases that activate HRAS. The duration and intensity of HRAS signaling help determine whether neural progenitors continue dividing or exit the cell cycle and differentiate into neurons. HRAS also influences neuronal migration, with appropriate signaling required for proper positioning of neurons in the developing brain. After migration, HRAS contributes to axonal and dendritic growth and branching. Studies in neuronal culture have shown that HRAS promotes dendritic arborization and spine formation, while excessive or insufficient HRAS signaling leads to abnormal morphology. The specific effects depend on the neuronal type and developmental context. Knockout of HRAS in mice results in viable animals with subtle behavioral phenotypes, suggesting compensatory mechanisms from other Ras family members, but complete deletion of all Ras isoforms leads to severe developmental defects. These findings highlight the importance of HRAS in neuronal development. [@wong2019]
HRAS is particularly important for the formation and maintenance of dendritic spines, the postsynaptic sites of most excitatory synapses in the brain. Dendritic spines are small protrusions from dendritic shafts that receive synaptic input from axonal terminals. The formation and remodeling of spines is activity-dependent and underlies synaptic plasticity, learning, and memory. HRAS signaling promotes spine formation through multiple mechanisms. First, HRAS-mediated MAPK/ERK activation leads to transcription of genes involved in spine development, including immediate early genes and synaptic proteins. Second, HRAS-PI3K-AKT signaling promotes the local synthesis of synaptic proteins at dendritic spines. Third, HRAS regulates the actin cytoskeleton through the RAL pathway, directly affecting spine morphology. Studies using fluorescently tagged HRAS have shown that it localizes to dendritic spines in an activity-dependent manner, with stronger recruitment during periods of high synaptic activity. Manipulating HRAS activity in neurons affects spine density and morphology. Overactive HRAS leads to increased spine density but abnormal spine shapes, while reduced HRAS impairs spine formation. These findings underscore the importance of precise HRAS regulation for proper synaptic connectivity. [@kim2015]
HRAS is essential for long-term potentiation (LTP), the cellular basis of learning and memory. LTP is a persistent strengthening of synapses that occurs in response to high-frequency stimulation or coincident pre- and postsynaptic activity. The requirements for LTP include NMDA receptor activation, calcium influx, and activation of intracellular signaling cascades. HRAS-mediated MAPK/ERK signaling is a critical component of the LTP induction and maintenance pathways. NMDA receptor activation leads to Ras activation through calcium-dependent mechanisms, and HRAS-GTP then initiates the MAPK/ERK cascade. Activated ERK translocates to the nucleus where it phosphorylates transcription factors and promotes gene expression required for LTP maintenance. Behavioral studies in mice have demonstrated that HRAS is required for memory formation. Forebrain-specific HRAS knockout mice show deficits in spatial learning and memory, as well as in fear conditioning. Conversely, activating HRAS in the hippocampus enhances memory consolidation. Human genetic studies have identified HRAS variants associated with cognitive function, though the molecular mechanisms remain under investigation. These findings establish HRAS as a key mediator of activity-dependent plasticity and memory formation. [@feng2010]
HRAS signaling in neurons is dynamically regulated by synaptic activity, providing a mechanism for linking neuronal experience to structural and functional plasticity. Synaptic activity leads to activation of receptor tyrosine kinases and G protein-coupled receptors that can activate HRAS through various GEFs. Calcium influx through NMDA receptors and voltage-gated calcium channels activates RasGRFs and other calcium-dependent GEFs. Membrane depolarization and elevated cAMP also contribute to activity-dependent HRAS activation. The dynamics of HRAS signaling are shaped by the kinetics of GEF and GAP activation, as well as by feedback mechanisms. ERK-dependent phosphorylation of HRAS itself can modulate its activity, creating both positive and negative feedback loops. The spatial distribution of HRAS activation within neurons is also regulated, with active HRAS-GTP accumulating at stimulated synapses. This localized signaling enables synapse-specific plasticity while sparing unstimulated synapses. The activity-dependence of HRAS signaling makes it well-suited to mediate the experience-dependent remodeling of neural circuits that underlies learning and memory. [@yeung2020]
HRAS has complex and multifaceted involvement in Alzheimer's disease (AD) pathophysiology. The MAPK/ERK pathway, which is activated by HRAS, is known to be dysregulated in AD brains, where it may contribute to both protective and pathogenic processes. On one hand, HRAS-ERK signaling can promote neuronal survival through activation of AKT and CREB-mediated gene expression. On the other hand, excessive or chronic ERK activation may contribute to amyloid-beta production, tau phosphorylation, and excitotoxicity. Amyloid-beta oligomers, the toxic species in AD, activate HRAS-MAPK signaling in neurons, potentially as part of a protective response that becomes maladaptive over time. Studies in cellular and animal models of AD have shown that inhibiting HRAS-MAPK signaling can reduce amyloid-beta toxicity, suggesting that pathway overactivation contributes to pathogenesis. HRAS also interacts with presenilin proteins and affects gamma-secretase activity, potentially influencing amyloid-beta production. Additionally, HRAS is involved in the regulation of tau phosphorylation through effects on GSK-3β and other kinases. The role of HRAS in synaptic dysfunction, a key early event in AD, is particularly relevant given its importance in spine formation and plasticity. Overall, HRAS appears to play a dual role in AD, with both protective and pathogenic effects depending on the cellular context and disease stage. Targeting HRAS-MAPK signaling therapeutically must consider this complexity. [@costa2011]
HRAS involvement in Parkinson's disease (PD) centers on its functions in dopaminergic neurons of the substantia nigra pars compacta. A genetic association study identified the HRAS Val96Ala variant (rs12628) as associated with reduced PD risk, suggesting that HRAS may influence dopaminergic neuron survival. The mechanism underlying this association remains under investigation, but HRAS-mediated signaling could affect multiple pathways relevant to PD pathogenesis. Dopaminergic neurons are particularly vulnerable to mitochondrial dysfunction, and HRAS signaling influences mitochondrial dynamics, reactive oxygen species production, and apoptosis. HRAS-MAPK signaling can promote either survival or death depending on the context, with chronic activation potentially contributing to neurodegeneration. The protein alpha-synuclein, which aggregates in PD, may interact with HRAS signaling pathways. Additionally, HRAS affects neuroinflammation, which is increasingly recognized as an important contributor to PD progression. Microglial HRAS signaling influences the inflammatory response, with implications for chronic neuroinflammation. Further research is needed to clarify the precise role of HRAS in PD and to determine whether targeting this pathway could be beneficial. [@chen2021]
Excitotoxicity, the pathological process by which excessive glutamate receptor activation leads to neuronal death, involves HRAS-MAPK signaling. Excessive glutamate release during stroke, traumatic brain injury, or neurodegenerative diseases can trigger excitotoxic cell death. While moderate activation of HRAS-MAPK signaling can be protective, excessive or prolonged activation contributes to excitotoxic damage. Studies have shown that inhibiting MAPK/ERK signaling can reduce excitotoxic neuronal death, suggesting that pathway overactivation is pathogenic. HRAS may also be involved in the regulation of NMDA receptor function and trafficking, potentially affecting excitotoxic vulnerability. Following ischemic injury, HRAS-MAPK signaling is activated in affected brain regions, contributing to both protective adaptive responses and damaging inflammatory processes. The dual nature of HRAS signaling in excitotoxicity complicates therapeutic targeting. Strategies that modulate rather than completely block HRAS-MAPK signaling may be more beneficial, allowing preservation of protective functions while reducing pathological activation. [@hernandez2018]
HRAS activation in neurons is regulated by multiple upstream inputs that translate synaptic activity and growth factor signaling into changes in Ras-GTP levels. Receptor tyrosine kinases including Trk receptors for BDNF and NGF activate HRAS through adaptor proteins such as Shc and GRB2, which recruit the RasGEF SOS. G protein-coupled receptors can also activate HRAS through protein kinase C-dependent pathways. Calcium influx through voltage-gated calcium channels and NMDA receptors activates RasGRF1 and RasGRF2, calcium-dependent RasGEFs that are particularly important in neurons. These calcium-dependent mechanisms provide a direct link between synaptic activity and HRAS activation. Additionally, cAMP-dependent protein kinase (PKA) can modulate HRAS signaling through phosphorylation of RasGAPs and RasGEFs. The convergence of multiple signaling pathways on HRAS enables integration of diverse inputs and appropriate cellular responses. Dysregulation of these upstream regulators can lead to abnormal HRAS signaling in disease states.
Activated HRAS-GTP interacts with multiple downstream effectors to mediate its cellular functions. The RAF kinases (A-RAF, B-RAF, C-RAF) are primary effectors that initiate the MAPK cascade. Different RAF isoforms have distinct expression patterns and functions in neurons, with B-RAF particularly important in the nervous system. PI3K is another major HRAS effector, with the p110 catalytic subunit directly binding HRAS-GTP. PI3K activation leads to AKT activation and promotion of cell survival. The RALGEFs (RGL, RLF) activate RAL GTPases that regulate vesicle trafficking and actin dynamics. PLCε is activated by HRAS and generates diacylglycerol and inositol trisphosphate, leading to calcium release and PKC activation. The diversity of downstream pathways allows HRAS to influence many aspects of neuronal function. Pathway selection is influenced by the specific HRAS conformations, effector availability, and subcellular localization. Feedback mechanisms ensure appropriate signal duration and termination.
HRAS interacts with numerous proteins beyond its canonical effectors, forming a complex signaling network in neurons. Scaffold proteins such as KSR (Kinase Suppressor of Ras) bring together components of the MAPK cascade, enhancing signaling efficiency and specificity. GAP proteins including p120GAP, NF1, and SynGAP provide crucial negative regulation of HRAS signaling in neurons. Chaperone proteins such as HSP90 assist in proper HRAS folding and stabilization. Postsynaptic density proteins including PSD-95 can interact with HRAS, localizing signaling to synapses. The protein cysteine-rich protein 1 (CRIP1) binds HRAS and modulates its membrane association. These interactions shape the specificity and spatial organization of HRAS signaling. Understanding the full HRAS interactome in neurons remains an important goal for understanding its functions.
Direct targeting of HRAS for neurodegenerative disease therapy is complicated by its essential functions and the complex roles it plays in different disease contexts. The most advanced therapeutic targeting of HRAS has occurred in cancer, where farnesyltransferase inhibitors (FTIs) that prevent HRAS prenylation and membrane localization have been developed. However, alternative prenylation pathways can compensate for FTIs in some contexts. In neurons, complete inhibition of HRAS would likely impair essential functions in synaptic plasticity and survival. More nuanced approaches may be needed. Modulating the downstream MAPK/ERK pathway through MEK or ERK inhibitors could provide therapeutic benefit while sparing some HRAS functions. However, systemic administration of these inhibitors has significant risks. Targeting specific neurons or brain regions could reduce side effects. An alternative approach is to enhance negative regulators of HRAS signaling, such as GAPs or endogenous inhibitors. Gene therapy approaches to deliver modified HRAS or HRAS regulators are under investigation.
HRAS expression and signaling may serve as biomarkers for neurological conditions. Changes in HRAS expression have been reported in brain tissue from patients with AD, PD, and other neurodegenerative diseases. HRAS mRNA and protein levels in peripheral blood cells may reflect CNS changes in some contexts. Genetic variants in HRAS have been associated with cognitive function and with neurodegenerative disease risk, as demonstrated by the HRAS Val96Ala association with PD. Phosphorylated ERK levels, downstream of HRAS, can be measured as a proxy for HRAS-MAPK pathway activity. Cerebrospinal fluid biomarkers that reflect HRAS signaling are being investigated. The development of PET ligands that image HRAS-MAPK signaling in vivo is an emerging area that could provide important insights into disease mechanisms and therapeutic response.
Significant questions remain about HRAS function in the nervous system. The specific roles of different Ras isoforms (HRAS, KRAS, NRAS) in neurons are not fully resolved, with partial functional redundancy complicating analysis. The spatial organization of HRAS signaling within neurons, and how this organization relates to synaptic plasticity, requires further investigation. The mechanisms by which HRAS variants contribute to neurodegenerative disease risk need clarification. The cell type-specific functions of HRAS in neurons versus glia are not completely understood. How HRAS signaling interacts with other pathways implicated in neurodegeneration, such as those involving tau, alpha-synuclein, and amyloid-beta, is an important area for future research. The development of better tools for studying HRAS, including improved sensors and selective modulators, will facilitate progress.
New technologies are enabling more detailed investigation of HRAS function. Genetically encoded biosensors allow visualization of HRAS-GTP levels in living neurons with subcellular resolution. Single-cell RNAseq is revealing cell type-specific HRAS expression patterns. Human induced pluripotent stem cell models enable study of HRAS variants in patient-derived neurons. Optogenetic approaches allow light-controlled activation of HRAS signaling. Proteomics approaches are mapping the HRAS interactome in neurons. These new tools promise to advance understanding of HRAS in the nervous system and may reveal new therapeutic opportunities.
The following diagram shows the key molecular relationships involving HRAS (Harvey Rat Sarcoma Viral Oncogene Homolog) discovered through SciDEX knowledge graph analysis: