ENTPD1 - ectonucleoside triphosphate diphosphohydrolase 1 |Elisa - Clia - Antibody - Protein

Background

ENTPD1, also known as CD39, is a critical ectoenzyme involved in the regulation of extracellular nucleotide levels. It belongs to the family of ectonucleoside triphosphate diphosphohydrolases (E-NTPDases) that hydrolyze extracellular nucleotides, such as ATP and ADP, into their respective monophosphate forms (AMP). This enzymatic activity is crucial for modulating purinergic signaling, which is involved in various physiological processes, including immune responses, thrombosis, vascular function, and tissue homeostasis.

ENTPD1 is primarily expressed on immune cells like T regulatory cells (Tregs), dendritic cells, macrophages, and endothelial cells. Its ability to degrade ATP and ADP limits pro-inflammatory and pro-thrombotic signaling, promoting an anti-inflammatory and antithrombotic environment. This makes ENTPD1 a significant player in maintaining immune tolerance, regulating inflammation, and controlling thrombosis.

Given its role in the immune system, ENTPD1 has become a target of interest in various diseases, including autoimmune disorders, cancer, cardiovascular diseases, and transplantation rejection. Its immunosuppressive functions, particularly in the tumor microenvironment, make ENTPD1 a key therapeutic target in immuno-oncology.

Protein Structure

The ENTPD1 protein consists of several structural domains critical for its enzymatic function. CD39 is a type II transmembrane glycoprotein, composed of an intracellular N-terminal domain, a single transmembrane helix, and a large extracellular C-terminal catalytic domain.

N-terminal Intracellular Domain:

• This short domain of about 20 amino acids is located within the cytoplasm. While not directly involved in catalytic function, the intracellular tail is important for protein localization and interactions with intracellular signaling pathways.

Transmembrane Helix:

• ENTPD1 has a single transmembrane helix that spans the plasma membrane, anchoring the protein and positioning the extracellular catalytic domain. The transmembrane domain ensures the proper orientation of ENTPD1 to facilitate its enzymatic activity on extracellular nucleotides.

Extracellular Catalytic Domain:

• The catalytic domain, located outside the cell, is the functional core of ENTPD1. This large extracellular region contains several conserved motifs essential for ATP and ADP hydrolysis, particularly the apyrase conserved regions (ACRs), which are present in all E-NTPDases. The catalytic activity of CD39 involves the coordinated binding of nucleotides to these regions and the subsequent hydrolysis of the phosphate bonds in the nucleotides.
• The active site of ENTPD1 contains calcium-binding sites, which are essential for stabilizing nucleotide interactions and the hydrolytic activity. The enzyme functions as a divalent cation-dependent hydrolase, meaning that it requires calcium or magnesium ions to facilitate the cleavage of the phosphate bonds in ATP and ADP.

Glycosylation Sites:

• ENTPD1 is a glycosylated protein, with several N-linked glycosylation sites in its extracellular domain. These glycosylations are crucial for the protein's stability, surface expression, and enzymatic activity. They help maintain the correct protein folding and can influence interactions with other proteins or receptors on the cell surface.

ENTPD1 primarily functions as a homodimer on the cell surface, with each subunit contributing to the overall enzymatic activity. This dimerization is thought to enhance its stability and optimize its activity in hydrolyzing extracellular nucleotides.

Classification and Subtypes

ENTPD1 belongs to the E-NTPDase family, which consists of eight members (NTPDase1-8), each with distinct tissue expression profiles and substrate specificities. ENTPD1 (CD39) is classified as NTPDase 1 and is distinguished by its ability to hydrolyze both ATP and ADP efficiently.

• Subtypes: While ENTPD1 itself does not have subtypes, the E-NTPDase family includes other isoforms like ENTPD2, ENTPD3, and ENTPD8, which exhibit varying enzymatic preferences for triphosphates versus diphosphates. ENTPD1 is unique in its ability to convert ATP/ADP to AMP, thus controlling the balance of pro-inflammatory ATP and anti-inflammatory adenosine in the extracellular space.

Function and Biological Significance

ENTPD1 plays a critical role in modulating purinergic signaling by degrading ATP and ADP, which are released from cells during stress, injury, or immune activation. ATP serves as a pro-inflammatory danger signal, while its degradation to adenosine by the combined actions of ENTPD1 and ecto-5’-nucleotidase (CD73) generates an anti-inflammatory signal.

The main functions of ENTPD1 include:

Immunomodulation:

• By degrading extracellular ATP, which acts as a pro-inflammatory signal through P2X and P2Y receptors, ENTPD1 limits inflammation and helps resolve immune responses. The resulting accumulation of adenosine promotes immune tolerance by activating adenosine receptors (A2A receptors), which suppress immune cell activation and promote the function of regulatory T cells (Tregs). This immunosuppressive function is particularly important in controlling chronic inflammation, autoimmunity, and transplant rejection.

Thromboregulation:

• In the vascular system, ENTPD1 prevents thrombosis by hydrolyzing ADP, a potent activator of platelet aggregation through P2Y12 receptors. By reducing ADP levels, ENTPD1 prevents excessive platelet activation and clot formation, thereby maintaining vascular homeostasis.

Tissue Protection:

• ENTPD1’s ability to limit ATP-driven inflammation plays a protective role in tissues exposed to chronic damage, such as in the context of ischemia-reperfusion injury, where extracellular ATP levels spike. Its role in generating adenosine also promotes tissue repair by reducing oxidative stress and inflammation.

Tumor Immune Evasion:

• In the tumor microenvironment, high ENTPD1 expression by tumor cells or tumor-infiltrating immune cells (e.g., Tregs and myeloid-derived suppressor cells) creates an immunosuppressive milieu. By degrading ATP and promoting adenosine accumulation, ENTPD1 limits the activity of cytotoxic T cells and natural killer cells, allowing tumors to escape immune surveillance. This has made ENTPD1 a target for immunotherapy in cancer.

Clinical Issues

ENTPD1 is involved in a range of clinical conditions due to its roles in immune regulation, vascular function, and purinergic signaling:

Cancer:

• In cancer, high ENTPD1 expression in the tumor microenvironment correlates with poor prognosis due to its role in immune suppression. ENTPD1 inhibitors are currently being explored in cancer immunotherapy to restore immune activity against tumors by reducing adenosine levels and enhancing cytotoxic T cell responses.

Autoimmune Diseases:

• In diseases like rheumatoid arthritis and systemic lupus erythematosus, where chronic inflammation is prevalent, targeting ENTPD1 to reduce ATP-mediated inflammation could be a therapeutic strategy. Additionally, modulating its activity might enhance the function of Tregs, which play a key role in controlling autoimmunity.

Thrombosis:

• Given ENTPD1’s role in regulating platelet aggregation, it has been implicated in conditions like deep vein thrombosis and myocardial infarction, where excessive clot formation occurs. Inhibition of ENTPD1 activity may elevate ADP levels and promote platelet aggregation, which can be either beneficial or detrimental depending on the clinical context.

Transplant Rejection:

• ENTPD1 plays a protective role in transplant settings by promoting immune tolerance and reducing inflammation. Higher levels of ENTPD1 activity are associated with reduced rates of transplant rejection. Strategies that enhance ENTPD1 function may improve graft survival.

Cardiovascular Diseases:

• ENTPD1 is a key player in preventing vascular inflammation and thrombosis. In cardiovascular diseases such as atherosclerosis, ENTPD1’s ability to modulate platelet function and vascular inflammation makes it a therapeutic target for reducing clot formation and promoting vascular health.

Summary

ENTPD1 (CD39) is a multifunctional ectonucleotidase involved in the regulation of extracellular ATP and ADP levels, thus playing a key role in modulating immune responses, thrombosis, and inflammation. Its protein structure consists of an N-terminal intracellular domain, a single transmembrane helix, and an extracellular catalytic domain that hydrolyzes nucleotides. ENTPD1’s enzymatic activity is crucial for controlling the balance between pro-inflammatory ATP and anti-inflammatory adenosine, with significant implications for tissue homeostasis, immune regulation, and vascular function.

Clinically, ENTPD1 is implicated in cancer, autoimmune diseases, thrombotic disorders, and transplant rejection, making it a valuable target for therapeutic interventions in these areas. Its precise modulation holds promise for the development of new treatments in immuno-oncology, autoimmune diseases, and cardiovascular health.