NOL3

Nucleolar protein 3 is a apoptosis-repressing protein that in humans is encoded by the NOL3 gene.

NOL3
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 4UZ0
Identifiers
Aliases	NOL3, ARC, FCM, MYP, NOP, NOP30, nucleolar protein 3, MYOCL1
External IDs	OMIM: 605235; MGI: 1925938; HomoloGene: 31208; GeneCards: NOL3; OMA:NOL3 - orthologs
Gene location (Human) Chr. Chromosome 16 (human)[1] Band 16q22.1 Start 67,170,154 bp[1] End 67,175,735 bp[1]
Gene location (Mouse) Chr. Chromosome 8 (mouse)[2] Band 8 D3|8 53.04 cM Start 106,002,772 bp[2] End 106,008,571 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in apex of heart gastrocnemius muscle skin of abdomen right adrenal gland right adrenal cortex skin of leg left adrenal gland body of pancreas muscle of thigh left adrenal cortex Top expressed in lumbar spinal ganglion extraocular muscle triceps brachii muscle sternocleidomastoid muscle temporal muscle digastric muscle ankle muscle of thigh thoracic diaphragm right ventricle More reference expression data BioGPS n/a
Gene ontology Molecular function death effector domain binding calcium ion binding death receptor binding metal ion binding cysteine-type endopeptidase inhibitor activity involved in apoptotic process protein binding RNA binding identical protein binding signaling receptor binding caspase binding Cellular component cytosol membrane sarcoplasmic reticulum sarcoplasm nucleus mitochondrion nucleolus cytoplasm Biological process regulation of apoptotic process release of sequestered calcium ion into cytosol by sarcoplasmic reticulum response to hypoxia negative regulation of striated muscle cell apoptotic process inhibition of cysteine-type endopeptidase activity involved in apoptotic process negative regulation of tumor necrosis factor-mediated signaling pathway negative regulation of muscle atrophy negative regulation of release of cytochrome c from mitochondria response to injury involved in regulation of muscle adaptation negative regulation of extrinsic apoptotic signaling pathway mRNA processing negative regulation of apoptotic process cardiac muscle cell apoptotic process intrinsic apoptotic signaling pathway negative regulation of cardiac muscle cell apoptotic process blood vessel remodeling response to ischemia mRNA splice site selection protein complex oligomerization negative regulation of mitochondrial membrane permeability involved in apoptotic process regulation of gene expression negative regulation of oxidative stress-induced intrinsic apoptotic signaling pathway negative regulation of necrotic cell death apoptotic process RNA splicing negative regulation of hypoxia-induced intrinsic apoptotic signaling pathway regulation of NIK/NF-kappaB signaling Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 8996 78688 Ensembl ENSG00000140939 ENSMUSG00000014776 UniProt O60936 Q9D1X0 RefSeq (mRNA) NM_001185057 NM_001185058 NM_001276307 NM_001276309 NM_001276311 NM_001276312 NM_001276319 NM_003946 NM_030152 RefSeq (protein) NP_001171986 NP_001263236 NP_001263238 NP_001263240 NP_001263241 NP_001263248 NP_003937 NP_084428 Location (UCSC) Chr 16: 67.17 – 67.18 Mb Chr 8: 106 – 106.01 Mb PubMed search [3] [4]
Wikidata
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The NOL3 gene in humans, codes for apoptosis-repressing proteins, including the apoptosis repressor with caspase recruitment domain (ARC), which is synonymous with the NOL3 protein, and the Nucleolar Protein.^[5][6] The NOL3 gene is found on Chromosome 16 in humans.^[7]

ARC

The apoptosis repressor with caspase recruitment domain (ARC) is a protein coded by Isoform 2 of the NOL3 gene due to alternative splicing.^[8] Human ARC is a cytoplasmic protein with the caspase recruitment domain (CARD). ARC is 208 amino acids containing the CARD N-terminal is fused to C-terminal of the protein which is full of proline (P) and glutamic acid (E) which was revealed via sequence analysis.^[8][9] Additionally, ARC protein is seen to be involved in inhibiting tumor necrosis factor α (TNFα) mediated regulated necrosis.^[10] The ARC protein is vital for inhibition of apoptosis which therefore plays a role in carcinogenesis.^[11] The ARC protein is over-expressed in varioius cancers and in pulmonary hypertension.^[9] ARC is seen to be expressed at high levels in the heart, which is seen as a benefit to prevent apoptosis in differentiated cardiomyocytes.^[12]

Structure

ARC protein is made up of two functional groups. The CARD region of the ARC protein is homologous to the other caspase recruite domains of caspase-2 and caspase adaptor RIP among other proteins. The CARD region is followed by a proline/glutamate tandem repeats that goes at the final 110 amino acids of ARC. This decreases the pH of the protein. This region can bind to free floating ions like calcium.^[13] CARD regions are not specific to the ARC protein and found in other apoptosis inhibiting proteins. They alls are the motifs of death domain reminants and apoptotic signaling. All CARD regions recruit caspase for apoptosis. Discovered in 1997 by K. Hoffmann et. all, the research are pivotal in ARC protein interactions and apoptotic inhibitions. Most CARD regions are inhibitory and the DED domain is another domain that can play the same role.

Function

The ARC protein has multiple ways of regulating or inhibition apoptosis. ARC is expressed in cardiomyocytes, neurons, and muscle cells, but is over-expressed in malignancies. Increase ARC expression leads to a lack of cellular recognition of apoptotic signals.^[9] Not only in cancer, but in autoimmune disease, viral infections, and degenerative disorders.^[14]

ARC Protein can regulate apoptosis via extrinsic or intrinsic pathways. Extrinsic pathways include caspase interaction and other death inducing signaling complexes.^[9]

Extrinsic inhibition

Caspase interaction

Although the mechanism for apoptosis inhibition by ARC is still to be further researched, speculation includes that the ARC protein targets immature caspase forms.^[14] Caspases are apoptosis effectors and regulate programmed cell-death. Cleavages occur predominately on C-terminal sides with aspartic acid (aspartate once deprotonated).^[15] Caspase activity is inhibited by the ARC protein. Specifically, the ARC protein interacts with caspase-2, caspase-8, and CED-3 but not with caspase -1, -3, or - 9. This interaction lead to inhibited cell signaling and programmed cell-death via the caspases.^[14]

FADD and TRADD interaction

ARC also inhibits programmed cell-death by affecting FADD and TRADD, which are two signaling molecules of signaling pathways that include proteins CD95/FAS and TNFR1. Expression usually results in apoptosis as the receptors activate the proteases caspase-8 along with caspase-2, but is regulated in the presence of ARC.^[14]

Intrinsic inhibition

BAX interaction

An apoptotic protein named BAX, which causes cytochrome c to release when activated is negatively affective by ARC. BAX is a mitochondrial indicator for apoptosis as oxidative stress leads to a conformational change to activated H9c2 cells. ARC and BAX interact directly and preserved mitochondrial integrity by preventing BAX activation.^[12]

p53 interaction

Transcription factor p53 is an important in carcinogenesis. Normally functioning p53 protein leads to the genomic stability, arrest of cell cycle, and apoptosis. However, a study has shown that inactivation can be attributed by the direct binding of p53 to the ARC protein nucleus. This then relocates the p53 to the cytoplasm, rendering it ineffective or significantly decreasing activity.^[16] ARC in cancer cells, induces the p53 to tetramerize to bind to the ARC nucleus, meaning the presence of the protein can lead to p53 inhibition. The study shows that only wild type p53 is inhibited by ARC protein and that mutated p53 is can be present in cancerous cells but is unaffected by the ARC protein.^[16]

Necrosis inhibition

Not only has ARC been found to inhibit apoptosis extrinsically and intrinsically, but also regulated form of necrosis. Necrosis, which differs to apoptosis by dysfunction of plasma membrane, cell and organelle swelling, and inflammation, can be regulated by death receptors. Tumor Necrosis Factor α (TNFα) which binds to tumor necrosis factor receptor 1 (TNFR1) then recruits death domains, receptor intercepting protain kinase 1 (RIP1), and other factors. This usually leads to caspase-8 activity and regular caspase apoptosis cascade. However, if caspase-8 is blocked, RIP1 and other kinases are activated, initiating necrosis. ARC is found to effect the necrosis pathway by interfering with RIP1 recruitment of TNFR1 which would thereby block necrosis. Caspase recruitment domain (CARD) is a necessary aspect to the ARC protein in regards to inhibiting necrosis. The study found that not only apoptosis inhibition but also necrosis inhibition relied on the presence of CARD.^[10]

NOP30

The Nucleolar Protein or NOP30 is a protein coded by Isoform 1 of the NOL3 gene due to alternative splicing.^[8] The "30" in the name comes for an expected 30 kD from the protein, which is actually larger than the expected 24 kD. The increase in actual kD is speculated to be from polar charge distribution between the CARD site and the carboxylic-terminal region of NOP30.^[13] NOP30 interacts with splicing factor SRp30c which may signal NOP30 having a role in pre-mRNA processing. For now, functions of NOP30 are being explored.^[8]

Structure

NOP30 and the ARC protein share a N-terminus but their C-terminus differs. NOP30 is more basic than the ARC protein, consisting of a C-terminus filled with arginines, serines, and prolines rather than the proline and glutamic acid filled C-terminus of ARC. Additionally, NOP30 is named in O. Stoss et. al's (1999) study due to the molecular weight of the protein being 30 kD.^[8]

Function

NOP30 is still being explored in terms of direct function. O. Stoss et. al (1999) do propose a possible novel function in terms of alternative splice site selection. Specifically, some serine/arginine (SR) proteins have a role in alternative pre-mRNA splicing.^[17] Concentration of these SR proteins can indicate splice selections on an mRNA strand. SRp30c is one of these SR proteins play a role in splice site selection. O. Stoss et. al (1999) found that the binding of NOP30 to SRp30c could lead to less SR protein concentration and thereby affecting alternative splice site selection on mRNA. NOP30 was proposed to also having an enhancing effect to SR proteins that cause alternative splicing.^[8] Further research is necessary for a more in-depth conclusion.

Clinical significance

Carcinogenesis

ARC has been shown to be induced in multiple cancer types and acts as a repressor of apoptosis leading to resistance and proliferation. Paradoxically, loss of NOL3 gene also leads to hematological disruption in mice resulting in a myeloproliferative neoplasm resembling primary myelofibrosis (PMF), and its deletion has also been detected in patient samples of PMF In PMF-like mouse models, NOL3 can play a possible tumor suppressing role in myeloid abnormalities.^[18]

ARC being related to apoptosis inhibition can lead to development of cancerous cells. Specifically, ARC carcinogenesis is induced by Ras proteins.^[11] Ras proteins are GTPases that when mutated at codons 12, 13, or 61, can have oncogenic effects.^[19] Ras can act as a transcription factor for ARC and induce NOL3 transcription. Additionally, Ras stabilizes ARC protein. Ras signaling has a possible function of decreasing activity of ubiquitin ligases specific to ARC and/or post-translational modification by Ras proteins decrease susceptibility to ubiquitination. This was specific to epithelial, breast, and colorectal cancers.^[11]

In a study by B. Carter et. al (2016), ARC played a pivotal role in the acute myeloid leukemia (AML). They found that ARC mediate a signaling pathway with protein NFkB and IL1β, a cytokine, that promotes resistance to chemotherapy in leukemic cells. In bone marrow microenvironments AML survival is dependent on ARC in regards to creating more cells to optimize for tumor growth.^[20]

In a study done by L. Wu et. al (2024), ARC (called NOL3 protein in the study) was found to also be an affector to malignancies with the bladder. This study found that cell proliferation in bladder cancer was reduced greatly once ARC was inhibited. Patients with high amounts of ARC in tumors found within the bladder had reduced overal survival. Overexpression of NOL3 in bladder cancer tumors leads to an unusual amount of cells being in the G1 phase. Regularly, cell cycle arrest would occur leading to cell accumlation at G1 phase. However, with ARC present, the cell cycle is modulated to for increased proliferation of malignant bladder cells. Additionally, the proliferation is also attributed to the ARC protein enhancing phosphorylation of the PI3k/Akt pathway.^[21]

In terms of colorectal cancer, the ARC protein is prevalent. A study done by I. Mercier et. al (2008) found that ARC abundance was high in most human colon cancer cell lines and all primary colon cancers. Based off this study, ARC protein levels in the colon can be used a signifer or determinate of colorectal cancer or risk. ARC was abundanct in 94.7% of the colorectal cancers tested in this study. In addition to colorectal cancer, this study concluded that human epithelial cancers of the ovar and cervix also had increased ARC abundance.^[22]

Chemo- and radiation-resistance

A study by I. Mercier et. al (2005) found that in human breast cancer cells, not only was ARC found in the cytosol and mitochondria but also unexpectedly found in the nuclei of both benign and malignant breast tissues. In addition to this, the study found that cytoplasmic ARC is a large contributor to human breast cancer tumors being resistant to chemo- and radiation therapy. Their methods included exposing and transfecting ARC into breast cancer cells. These breast cancer cells that now contained high levels of arc were then exposed to cancer treatments, doxorubicin or γ-radiation. They found that the highest number of surviving cells were found in the breast cancer cells transfected with ARC. Within the study, the found this evidence as an indicator for ARC being a contributor to chemo- and radiation resistance.^[23]

Myocardial infarction

T. Le et. al (2012) explored the role of ARC and the protein's possible benefit in reducing morbidity and morality in regards to myocardial infarction. T. Le et. al wanted to focus on preventing degredation of ARC in the myocardium so that during apoptosis/programmed cell-death was less likely to occur. In order to prevent degredation of ARC and maintain concentration of the apoptosis repressor, a low-dose mineralcorticoid receptor antagonist was used, specifically either spironolactone or eplerenone. Ischemia was a focus as the blockage of blood to areas within the myocardium could lead to apoptosis.^[24]

Hippocampal neurogenesis

G. Kronenberg et. al (2019) found that hippocampus neuron generation was reduced if the ARC protein was not present in mice. New generated cells in the adult hippocampus with mice are predominately eliminated by programmed cell-death. G. Kronenberg et. al (2019) found that if the ARC protein is not present to inhibit apoptotic mechanisms either intrinsically or extrinsically, the disregulation of hippocampus cell apoptosis would occur more frequently. This study further builds the ARC function for apoptosis inhibition but in regards to the brain and neurogenesis.^[25]

Cortical myoclonus

There has been some research that a NOL3 gene mutation may have some connection to familial cortical myoclonus. A study done in 2012 by J. Russell et. al observed 11 members of a Canadian Mennonite family suffering myoclonus. They observed an autosomal dominant inherited, single cosegregating, novel, non-synonymous mutation on NOL3.^[17] However, a study published in 2014 by A. Macerollo had screened 107 patients with myoclonic jerks and only a single subject had a single nucleotide mutation in NOL3.^[17] Further conclusive evidence is still required for a full causal or correlative conclusion between NOL3 and familial cortical myoclonus.