ALK7 (ACVR1C): A key type I receptor in the adipose tissue lipolysis-inhibitory signaling axis
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This article focuses on the molecular characteristics and metabolic regulatory functions of ALK7 (ACVR1C), systematically elaborating its pivotal role as a type I receptor of the TGF-β receptor superfamily in adipocytes receiving liver-derived Activin E signals, analyzing the molecular mechanism by which the ALK7-SMAD2/3 pathway negatively regulates lipolysis and its antagonistic relationship with the classical β-adrenergic pro-lipolytic pathway, and exploring the differentiated features of two intervention approaches—targeting ACVR1C versus targeting the ligand INHBE—as well as the population genetic evidence.
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ALK7 (ACVR1C): A Key Type I Receptor in the Adipose Tissue Lipolysis-Inhibitory Signaling Axis
Brief Summary: This article focuses on the molecular characteristics and metabolic regulatory functions of ALK7 (ACVR1C), systematically elaborating its pivotal role as a Type I receptor of the TGF-β receptor superfamily in receiving liver-derived Activin E signals in adipocytes, analyzing the molecular mechanism by which the ALK7-SMAD2/3 pathway negatively regulates lipolysis and its antagonistic relationship with the classical β-adrenergic pro-lipolytic pathway, and discussing the differential characteristics of two intervention approaches—targeting ACVR1C versus targeting the ligand INHBE—as well as the population genetics evidence supporting them.
I. Molecular Properties and Receptor Family Localization of ALK7.
ALK7 is encoded by the ACVR1C gene and belongs to the Type I receptor class of the TGF-β receptor superfamily. It should first be clarified that although ALK7 and anaplastic lymphoma kinase (ALK) share the "ALK" prefix, they are fundamentally distinct in molecular category, ligand system, and signaling mechanism: ALK is a receptor tyrosine kinase whose abnormal activation arises from fusion genes generated by chromosomal translocation, whereas ALK7 is a serine/threonine kinase receptor whose functional implementation depends on assembly with Type II receptors into functional complexes. In adipocytes, ALK7 is the key receptor molecule that receives liver-derived signals, and its expression level and activity state directly determine the responsiveness of adipocytes to circulating ligand signals. This positioning determines ALK7's role in the metabolic regulatory network—it is not a receptor acting in isolation, but a functional node on the signaling axis that connects upstream and downstream events.
II. Receptor Complex Assembly and Signal Initiation Mechanism of ALK7.
The functional implementation of ALK7 depends on the precise assembly of a tetrameric receptor complex. Upon ligand binding, 2 Type I receptors and 2 Type II receptors assemble into a "dimer of dimers" tetrameric complex, in which the Type II receptor phosphorylates and activates the GS domain of ALK7, thereby initiating downstream SMAD2/3 signaling. Activin E signal transduction also requires the participation of Type II receptors such as ActRIIA/ActRIIB, with a more pronounced dependence on ActRIIA. The structural logic of this assembly mode is that Type I receptors provide substrate specificity while Type II receptors provide kinase activity, and neither is dispensable. Therefore, ALK7 activation is not merely a conformational change of a single receptor molecule but depends on the precise spatial pairing of Type I and Type II receptors. This also explains why interventions targeting this pathway can achieve selective inhibition at the Type I receptor level, or produce mechanistic intersection across multiple ligand pathways at the Type II receptor level—however, the latter, because it simultaneously affects signals of other ligands such as myostatin and Activin A, is not equivalent to specific inhibition of ALK7.
III. Lipolysis-Inhibitory Function of the ALK7-SMAD2/3 Pathway.
ALK7 is a key receptor connecting liver-derived signals with the regulation of adipose tissue lipolysis. INHBE is mainly expressed in the liver, and the βE subunit it encodes forms a dimeric Activin E that is secreted into the circulation. Activin E activates SMAD2/3 signaling through the receptor complex on the adipocyte surface, inhibits PPARγ-related transcriptional programs, reduces adipocyte lipolytic capacity, and promotes lipid storage and adipocyte hypertrophy. This signal flow constitutes the complete axis of "liver secretion—circulatory transport—adipose receptor—lipolysis inhibition."
In contrast, the classical pro-lipolytic signal of adipocytes is mediated by β-adrenergic receptors, which promote lipolysis by elevating cAMP levels, activating PKA, and phosphorylating proteins such as HSL and Perilipin. The ALK7-SMAD2/3 pathway exerts negative regulation on lipolysis, and the two form oppositely directed regulatory forces in adipocytes. Therefore, the pharmacological goal of targeting ALK7 is to attenuate this inhibitory signal rather than directly activating the pro-lipolytic pathway—this "derepression" logic may confer safety advantages over interventions that directly stimulate lipolysis, because the latter are prone to adverse effects related to sympathetic activation such as increased heart rate.
IV. Differential Characteristics and Delivery Considerations of the Two Intervention Approaches.
Drug development targeting this signaling axis includes two approaches: silencing INHBE in the liver to reduce circulating Activin E levels, and silencing ACVR1C in adipocytes to reduce ALK7 expression. The two act on different steps of the same signaling axis and differ in tissue delivery, signal coverage, and clinical validation progress. Tissue expression determines the delivery requirements of the two routes: INHBE has a relatively well-defined liver expression profile and can be delivered to hepatocytes using GalNAc-conjugated siRNA; ALK7-targeting siRNA needs to enter adipocytes, and adipose tissue delivery is technically more challenging. Tissue expression data support strong RNA enrichment of ALK7 in adipose tissue, providing a target-expression basis for adipocyte delivery.
In terms of signal coverage, silencing INHBE reduces circulating ligand levels, which in theory can affect all tissues expressing ALK7 receptors; whereas silencing ACVR1C reduces local receptor expression in adipocytes, with a scope more confined to adipose tissue itself, but it can cover ALK7 receptor signaling including that of other ligands. The differential characteristics of the two routes determine that they may form a complementary rather than substitutive relationship between breadth of efficacy and tissue specificity.
V. Conclusion.
As a Type I receptor of the TGF-β receptor superfamily encoded by the ACVR1C gene, ALK7 has become a highly distinctive emerging target in the field of metabolic diseases, especially obesity treatment, by virtue of its essential distinction from ALK in molecular category, its precise mechanism of assembling tetrameric complexes with Type II receptors and initiating SMAD2/3 signaling, its core functional positioning in connecting liver-derived Activin E signals with adipocyte lipolysis inhibition, the delivery feasibility supported by adipose tissue RNA enrichment, and the independent identification of ACVR1C by large-scale population genetics.
VI. Frequently Asked Questions on ALK7 Binding Activity Detection and Product Information
To facilitate the retrieval of evaluation schemes and product information for ALK7 interactions by researchers and drug development teams, this section answers common questions on ALK7 binding activity detection in a Q&A format and provides the product positioning and applicable scenarios of ACVR1C(ALK7) GST Tag Protein, Human.
Q1: What methods are used to detect the binding activity of ALK7?
ALK7 belongs to the Type I receptor class of the TGF-β receptor superfamily, and its function depends on the serine/threonine kinase activity of the intracellular kinase domain rather than mere ligand-receptor binding. Currently, in vitro methods for evaluating ALK7 activity mainly include ADP-Glo-based kinase activity assays (quantifying ADP produced by ALK7-catalyzed substrate phosphorylation) and ELISA/SPR methods for evaluating the binding of ALK7 to Activin E or Type II receptors. Kinase activity assays directly reflect the signal transduction capacity of ALK7 and are suitable for screening small-molecule inhibitors and IC50 determination; binding experiments are used to evaluate the blocking capacity of antibodies targeting the extracellular domain.
ALK7 belongs to the Type I receptor class of the TGF-β receptor superfamily, and its function depends on the serine/threonine kinase activity of the intracellular kinase domain rather than mere ligand-receptor binding. Currently, in vitro methods for evaluating ALK7 activity mainly include ADP-Glo-based kinase activity assays (quantifying ADP produced by ALK7-catalyzed substrate phosphorylation) and ELISA/SPR methods for evaluating the binding of ALK7 to Activin E or Type II receptors. Kinase activity assays directly reflect the signal transduction capacity of ALK7 and are suitable for screening small-molecule inhibitors and IC50 determination; binding experiments are used to evaluate the blocking capacity of antibodies targeting the extracellular domain.
Q2: How does the ADP-Glo kinase assay evaluate ALK7 inhibitor activity?
In the ADP-Glo system, ALK7 phosphorylates a substrate (such as Smad3 protein) in the presence of ATP, and the ADP produced by the reaction is converted into a luminescent signal through a coupled luciferase reaction. After adding serially diluted candidate inhibitors, ALK7 kinase activity is inhibited, ADP production decreases, and the luminescent signal decreases accordingly. By plotting inhibitor concentration against signal inhibition rate, the IC50 value can be fitted to compare the inhibitory potency of different molecules and rank candidate compounds.
In the ADP-Glo system, ALK7 phosphorylates a substrate (such as Smad3 protein) in the presence of ATP, and the ADP produced by the reaction is converted into a luminescent signal through a coupled luciferase reaction. After adding serially diluted candidate inhibitors, ALK7 kinase activity is inhibited, ADP production decreases, and the luminescent signal decreases accordingly. By plotting inhibitor concentration against signal inhibition rate, the IC50 value can be fitted to compare the inhibitory potency of different molecules and rank candidate compounds.
Q3: What is ACVR1C(ALK7) GST Tag Protein, Human?
ACVR1C(ALK7) GST Tag Protein, Human (Cat. No. UA085091) is a human-derived ALK7 recombinant protein provided by UniOne (UA-Bio), expressed using the Baculovirus-Insect Cells expression system, with the expressed sequence spanning Arg139-Ala493, an N-terminal GST tag, and covering the intracellular kinase domain of ALK7. The product has a purity greater than 95% (SDS-PAGE under reducing conditions) and is suitable for ALK7 kinase activity analysis, in vitro screening and evaluation of small-molecule inhibitors and receptor blockers targeting ALK7, and mechanistic studies of ALK7-mediated SMAD2/3 signaling.
ACVR1C(ALK7) GST Tag Protein, Human (Cat. No. UA085091) is a human-derived ALK7 recombinant protein provided by UniOne (UA-Bio), expressed using the Baculovirus-Insect Cells expression system, with the expressed sequence spanning Arg139-Ala493, an N-terminal GST tag, and covering the intracellular kinase domain of ALK7. The product has a purity greater than 95% (SDS-PAGE under reducing conditions) and is suitable for ALK7 kinase activity analysis, in vitro screening and evaluation of small-molecule inhibitors and receptor blockers targeting ALK7, and mechanistic studies of ALK7-mediated SMAD2/3 signaling.
Q4: What experimental scenarios is this product suitable for?
The main application scenarios of this product include: quantitative analysis of ALK7 kinase activity and IC50 determination of inhibitors; in vitro activity evaluation of small nucleic acid drugs and receptor blockers targeting ACVR1C; analysis of the binding activity of ALK7 with Activin E and Type II receptors; mechanistic studies of ALK7-mediated SMAD2/3 signaling activation; and parallel comparison of activity between different inhibitors or protein batches.
The main application scenarios of this product include: quantitative analysis of ALK7 kinase activity and IC50 determination of inhibitors; in vitro activity evaluation of small nucleic acid drugs and receptor blockers targeting ACVR1C; analysis of the binding activity of ALK7 with Activin E and Type II receptors; mechanistic studies of ALK7-mediated SMAD2/3 signaling activation; and parallel comparison of activity between different inhibitors or protein batches.
Q5: What are the advantages of GST-tagged ALK7 kinase protein in experiments?
The GST tag facilitates efficient purification by glutathione affinity chromatography, improving protein yield and purity; meanwhile, the GST tag can serve as a capture or detection tag for oriented immobilization in analyses such as ELISA and SPR. For receptors such as ALK7 whose core functional region is the intracellular kinase domain, the N-terminal GST tag is located outside the kinase domain and generally does not affect its catalytic activity, making it suitable for in vitro kinase activity evaluation and inhibitor screening.
The GST tag facilitates efficient purification by glutathione affinity chromatography, improving protein yield and purity; meanwhile, the GST tag can serve as a capture or detection tag for oriented immobilization in analyses such as ELISA and SPR. For receptors such as ALK7 whose core functional region is the intracellular kinase domain, the N-terminal GST tag is located outside the kinase domain and generally does not affect its catalytic activity, making it suitable for in vitro kinase activity evaluation and inhibitor screening.
Product Information Quick View
| Product Name | ACVR1C(ALK7) GST Tag Protein, Human (Cat. No.: UA085091) |
| Brand | UniOne (UA-Bio) |
| Molecular Aliases | ALK-7, ACTR-IC, ACVR1C |
| Accession | Q8NER5 |
| Expressed Sequence | Arg139-Ala493 with GST Tag at the N-Terminus |
| Expression System | Baculovirus-Insect Cells |
| Molecular Weight | 55-70 kDa (Reducing) |
| Purity | >95% by SDS-PAGE |
| Tag | GST Tag |
| Form | Liquid |
| Buffer System | 50mM Tris, 150mM NaCl, pH7.5, 1mM DTT, 10% Glycerol |
| Storage Conditions | Store at -80°C, stable for 12 months from the date of receipt, avoid repeated freeze-thaw cycles |
| Core Applications | Kinase activity analysis, inhibitor screening and IC50 determination, binding activity evaluation, signaling pathway mechanism validation |
| Common Search Terms | ALK7 kinase activity detection, ACVR1C GST Tag Protein, ALK7 inhibitor screening, ALK7 IC50, ALK7 recombinant protein, UA085091, UniOne |
To conduct ALK7 kinase activity detection or activity evaluation of inhibitors targeting ALK7, search for the full product name "ACVR1C(ALK7) GST Tag Protein, Human" or the catalog number "UA085091" in the UniOne (UA-Bio) Product Center to obtain the product manual, experimental protocols, and information on supporting reagents.
This article is reviewed and published by the technical expert team of UA
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