Recombinant Human Bone morphogenetic protein receptor type-1A (BMPR1A)
Description
Biological Activity and Signaling Mechanisms
Ligand Interactions:
Signaling Pathways:
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Canonical SMAD Pathway: Ligand binding induces heterotetrameric complex formation with BMPR2, activating SMAD1/5/8. Phosphorylated SMADs complex with SMAD4, translocate to the nucleus, and regulate gene transcription .
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Non-Canonical Pathways: Modulates MAPK and PI3K/AKT pathways, influencing apoptosis and differentiation .
Functional Assays:
| Assay Type | ED50/Activity | Cell Line | Reference |
|---|---|---|---|
| Alkaline phosphatase inhibition | 120 ng/mL (BMP-4) | ATDC5 cells | |
| Chondrocyte differentiation | 1.4 nmol/min/mg specific activity | Sf9-derived |
Research Applications and Findings
Key Studies:
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Germinal Center B-Cell Dynamics: BMPR1A deficiency reduces long-lived plasma cells and memory B cells, highlighting its role in immune memory .
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Craniofacial Development: Conditional Bmpr1a knockout mice exhibit cleft palate and calvarial defects due to impaired neural crest cell survival .
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Osteogenesis: BMPR1A is indispensable for extracellular matrix deposition by osteoblasts, though not for osteoblast proliferation .
Therapeutic Potential:
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Regenerative Medicine: Promotes chondrogenic differentiation and tissue repair in preclinical models .
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Disease Models: Linked to juvenile polyposis syndrome (JPS) via mutations causing disrupted TGF-β signaling and unregulated cell growth .
Comparative Analysis of Expression Systems
| Parameter | CHO Cells | Sf9 Cells | HEK293 Cells |
|---|---|---|---|
| Glycosylation | Human-like | Insect-specific | Human-like |
| Yield | High | Moderate | High |
| Cost | Expensive | Moderate | Expensive |
| Preferred Use | Therapeutic studies | Structural studies | Signaling pathway analysis |
Future Directions
Product Specs
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Target Background
Upon ligand binding, BMPR1A forms a receptor complex with two type II and two type I transmembrane serine/threonine kinases. Type II receptors phosphorylate and activate type I receptors, which then undergo autophosphorylation and subsequently bind and activate SMAD transcriptional regulators. BMPR1A serves as a receptor for BMP2, BMP4, GDF5, and GDF6. It positively regulates chondrocyte differentiation through GDF5 interaction and mediates the induction of adipogenesis through GDF6 interaction.
- Single nucleotide polymorphisms (SNPs) in the BMPR1A gene have shown significant associations with the development of ossification of the posterior longitudinal ligament of the cervical spine. PMID: 29458345
- BMPR1A mutations have been implicated in superior coloboma. PMID: 29522511
- Knockdown of BMPR1A in breast cancer cells suppresses RANKL production via the p38 pathway, inhibiting cancer-induced osteoclastogenesis. PMID: 29495003
- BMPR1A and the ubiquitous isoform of BMPR1B differ in endoplasmic reticulum translocation and glycosylation, influencing their processing and plasma membrane expression. PMID: 28357470
- Several germline variants in genes associated with Hamartomatous Polyposis Syndrome, including BMPR1A, have been identified. PMID: 27146957
- Hepatic nuclear factor 4 alpha (HNF-4α) appears to suppress hepcidin expression by inactivating the BMP pathway, specifically through BMPR1A, in HepG2 cells. PMID: 27660075
- Protein kinase LKB1 interacts with BMP type I receptors and requires Smad7 to downregulate these receptors. PMID: 26701726
- Adipose-derived mesenchymal stem cells expressing BMPR1A exhibit enhanced adipogenesis in vitro. PMID: 26585335
- Duplication of 10q22.3-q23.3, encompassing BMPR1A, is associated with congenital heart disease, microcephaly, and mild intellectual disability. PMID: 26383923
- High BMPR1A gene expression correlates with decreased survival in breast cancer, irrespective of molecular subtype. PMID: 26274893
- Loss of heterozygosity, predominantly in the epithelial compartment, is observed in about half of BMPR1A-related polyps, consistent with its role as a tumor suppressor gene. PMID: 26171675
- miR-885-3p regulates tumor angiogenesis by targeting BMPR1A, which in turn regulates a proangiogenic factor. PMID: 24882581
- Decreased BMPR1A expression is associated with malignant gallbladder lesions. PMID: 23531103
- Higher BMPR1A mRNA/protein expression is observed in stenotic colon segments compared to normal colon segments in Hirschsprung disease patients. PMID: 24966941
- High BMPR1A expression is associated with glioma tumorigenesis. PMID: 24480809
- USP15 enhances BMP-induced SMAD1 phosphorylation by interacting with and deubiquitinating ALK3. PMID: 24850914
- A coding exon 3 duplication in the BMPR1A gene has been reported in a patient with juvenile polyposis syndrome. PMID: 25129392
- HFE induces hepcidin expression via the BMP pathway by interacting with ALK3 to stabilize ALK3 protein and increase its cell surface expression. PMID: 24904118
- BMP15 downregulates StAR expression and progesterone production in human granulosa cells, likely through ALK3-mediated SMAD1/5/8 signaling. PMID: 24140593
- BMPR1A and BMPR2 are downregulated in cardiac remodeling and heart failure. PMID: 24398041
- Missense mutations in BMPR1A in patients with juvenile polyposis affect cellular localization in vitro. PMID: 23433720
- Reduced BMPR1A expression is associated with a poorer prognosis in pancreatic cancer. PMID: 23969729
- BMP receptor antagonists and siRNA silencing of BMP type I receptors induce cell death, inhibit cell growth, and decrease the expression of inhibitor of differentiation (Id) family members. PMID: 23593444
- Colorectal polyposis-associated mutations, including those in BMPR1A, have been identified in a significant number of patients. PMID: 23399955
- The BMPR1A rs7922846 polymorphism may influence kidney size at birth, reflecting congenital nephron endowment. PMID: 22886282
- No associations were found between left ventricular mass (LVM), blood pressure, and the BMP4, BMPR1A, BMPR1B, and ACVR1 genotypes. PMID: 22971142
- BMPR1A may serve as an indicator of osteoarthritis progression in human knees with circumscribed cartilage lesions. PMID: 22519633
- Crystallographic studies have been performed on the GDF5 and BMP receptor IA complex. PMID: 21543859
- Review article on TGF-β and BMP receptor homo- and hetero-oligomerization and its role in regulating signaling. PMID: 22293501
- Review article analyzing promiscuity and specificity in BMP receptor activation. PMID: 22710174
- Sp1 is a candidate transcriptional regulator of BMPR1A. PMID: 21872883
- Report on the phenotypic spectrum of BMPR1A mutations in hereditary nonpolyposis colorectal cancer without mismatch repair deficiency. PMID: 21640116
- Blocking both endogenous BMPR1A and BMPR1B largely offsets the effect of BMP7 on NCI-H460 cell proliferation. PMID: 20673479
- Juvenile polyps with SMAD4 germline mutations are predominantly type B, while type A is more common with BMPR1A germline mutations. PMID: 21412070
- Identification of the BMPR1A promoter, mutations in which may account for up to 10% of juvenile polyposis cases with unknown mutations. PMID: 20843829
- BMPR1A has been detected in the human retina and retinoblastoma cell lines. PMID: 21152263
- Crystallographic studies have been performed on the BMP receptor type IA bound to an antibody Fab fragment. PMID: 20693682
- Description of a BMPR1A gene mutation in an Irish family with hereditary mixed polyposis syndrome. PMID: 19438883
- Germline BMPR1A defects account for approximately 50% of hereditary mixed polyposis syndrome (HMPS) families. PMID: 19773747
- BMPR1A may act as a minor susceptibility gene for PTEN mutation-negative Cowden syndrome. PMID: 12620973
- BMPR1A may interact with and modulate the activity of a developmentally relevant splicing factor. PMID: 15351706
- Altered BMP receptor trafficking, potentially due to defects in BMPR1A internalization, may underlie ectopic bone formation in fibrodysplasia ossificans progressiva. PMID: 15940369
- BMPR1A is a potential marker for evaluating ganglion cells in the enteric nervous system. PMID: 16226113
- The human granulosa-like tumor cell line KGN expresses BMP type I (BMPR1A and BMPR1B) and type II receptors (BMPR2), and the BMP signaling molecules SMADs (SMAD1 and SMAD5). PMID: 16436528
- BMPR1A mutations are implicated in hereditary mixed polyposis syndrome and inactivation of this gene can initiate colorectal tumorigenesis. PMID: 16525031
- Deletion of the BMPR1A and PTEN genes on chromosome 10 occurs in juvenile polyposis coli. PMID: 17101085
- SF3b4, a nuclear RNA splicing factor, binds BMPR1A and inhibits BMP-mediated osteochondral cell differentiation. PMID: 17513295
- Linkage analysis suggests a cryptic BMPR1A mutation or the presence of another gene near the BMPR1A locus. PMID: 17573831
- Several mutations in BMPR1A (nonsense, frameshift, missense, and splice site) have been associated with juvenile polyposis syndrome. PMID: 17873119
- Large genomic deletions of SMAD4, BMPR1A, and PTEN are a common cause of juvenile polyposis syndrome (JPS). PMID: 18178612
Q&A
What is the basic structure and function of BMPR1A?
BMPR1A (also known as CD292, ACVRLK3, ALK3) is a type I transmembrane serine/threonine kinase receptor belonging to the TGF-β receptor subfamily of the protein kinase superfamily. The receptor consists of 532 amino acids, with functional domains including an extracellular ligand-binding domain, a transmembrane region, and an intracellular kinase domain.
On ligand binding, BMPR1A forms a receptor complex consisting of two type II and two type I transmembrane serine/threonine kinases. The type II receptors phosphorylate and activate type I receptors like BMPR1A, which then autophosphorylate, bind and activate SMAD transcriptional regulators, ultimately influencing gene expression .
BMPR1A serves as a receptor for multiple bone morphogenetic proteins including BMP2, BMP4, GDF5, and GDF6. It positively regulates chondrocyte differentiation through GDF5 interaction and mediates induction of adipogenesis by GDF6. It may also promote the expression of HAMP (hepcidin), potentially via its interaction with BMP2 .
How is the BMPR1A gene structured and regulated?
The BMPR1A gene has a complex structure that includes both coding and non-coding (NC) exons. Research has identified four non-coding exons and two putative promoters (designated as promoter A and promoter B) . Analysis of these promoters indicates that promoter B appears to be the most important for BMPR1A expression, though promoter A may play roles in different tissues or developmental stages .
The BMPR1A promoter region contains several regulatory elements including binding sites for transcription factors such as:
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Myeloid zinc finger 1 factor (MZF1)
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SP-1
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E2F
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AP-2
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RNA PolII transcription 2B-binding site (TF2B)
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Core promoter motif 10 (MTEN) element
This 520 bp regulatory region shows conservation across species, with 47% orthology to the brown rat and 68% to the wild boar, confirming the potential relevance of these regulatory elements .
What are the optimal methods for detecting and quantifying BMPR1A expression?
For detecting and quantifying BMPR1A expression, researchers have successfully employed several complementary techniques:
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Protein Quantification: ELISA assays can be used to measure BMPR1A protein levels in lymphoblastoid cell lines (LCLs). This technique has been used to demonstrate that individuals with promoter mutations or deletions show reduced BMPR1A protein levels (approximately 27-43% of normal control levels) .
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Gene Expression Analysis: Quantitative PCR (qPCR) has been effectively used to measure BMPR1A mRNA expression. Novel reporter mice (BMPR1A.IRES.EGFP) have also been developed to monitor expression patterns in different cell populations .
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Protein Detection: Western blotting using recombinant BMPR1A protein (fragment range 187-532 aa) as positive control can help validate antibodies and optimize detection protocols .
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Promoter Activity Assays: Luciferase reporter assays can be employed to evaluate promoter activity. This approach has been used to assess how various mutations affect BMPR1A promoter function. For example, a deletion at positions -150 to -1 resulted in complete loss of promoter activity, while point mutations led to variable reductions in activity (24-53% of wild-type activity) .
What experimental models are available for studying BMPR1A function?
Several experimental models have been developed to study BMPR1A function:
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Cell Lines: Human embryonic kidney cells (HEK-293) and normal colon epithelial cells (CRL-1459) have been used for promoter activity studies .
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Lymphoblastoid Cell Lines (LCLs): These can be established from patients with BMPR1A mutations to study protein expression and functional consequences .
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Conditional Knockout Mice: Cell-specific deletion of BMPR1A using Cre-lox systems has been instrumental in defining tissue-specific roles:
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Recombinant Protein Systems: Baculovirus-infected Sf9 cells have been used to express recombinant human BMPR1A protein fragments (187-532 aa range) with >90% purity for functional studies .
How are BMPR1A mutations linked to juvenile polyposis syndrome?
Juvenile polyposis (JP) is an autosomal dominant hamartomatous polyposis syndrome where affected individuals are predisposed to colorectal and upper gastrointestinal cancer. Approximately 45% of JP patients have mutations or deletions involving the coding regions of SMAD4 and BMPR1A .
Research has identified various types of BMPR1A genetic alterations in JP patients:
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Promoter Mutations: Mutations affecting the BMPR1A promoter may be responsible for as many as 10% of JP cases with unknown mutations. In one study, 6 of 65 JP probands were found to have mutations affecting the BMPR1A promoter .
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Protein Expression Impact: All tested JP probands with promoter mutations showed diminished BMPR1A protein levels by ELISA, ranging from 27-43% of normal control levels .
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Functional Effects: Nearly all promoter mutations led to significantly reduced luciferase activity relative to the wild-type promoter, with reductions ranging from 47-76% .
The following table summarizes genetic alterations found in JP patients and their effects:
| Proband | Genetic Alteration | Affected Binding Sites | Protein Level | Luciferase Activity |
|---|---|---|---|---|
| 19 | Del −150 to −1 | 2 MZF-1, TF2B, 2 SP-1 | 39% | 0 |
| 86 | −224 T/T>A/T | ZF5F | Not done | 24 |
| 100 | −306 G/G>C/G | E2F | 43% | 53 |
| 117 | −328 G/G>T/G | MZF-1 | 27% | 45 |
| 42 | −328 G/G>T/G | MZF-1 | Not done | 45 |
| 13 | −386 G/G>A/G | None identified | 31% | 104 |
What is the evidence for BMPR1A's role in congenital heart defects?
BMPR1A has been identified as a candidate gene for congenital heart defects, particularly atrioventricular septum defects. A de novo intragenic deletion of the BMPR1A gene was detected in a normally developing 17-year-old boy with an atrioventricular septum defect .
The deleted region in this case spanned approximately 22 kb, disrupting the promoter and first non-coding exon of the BMPR1A gene. The proximal and distal breakpoint containing regions were situated between 88,514,385 and 88,535,831 .
Similar intragenic BMPR1A deletions involving the promoter and first non-coding exon have been detected by multiplex ligation-dependent probe amplification (MLPA) in screening surveys for juvenile polyposis syndrome, suggesting that such deletions interfere with normal human physiology .
How does BMPR1A signaling influence immune system development and function?
BMPR1A plays critical roles in immune system function, particularly in B cell responses and memory formation. Studies using BMPR1a.IRES.EGFP reporter mice have demonstrated that BMPR1A expression is upregulated among germinal center B cells (GCBC) and subsets of memory B cells (MBC), bone marrow plasmablasts, and bone marrow plasma cells (BMPC) .
In mice with B cell-targeted BMPR1A gene deletions, researchers observed several significant immunological effects:
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Initial GC Response: The germinal center response was initially diminished .
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Selective Pressure: The GCBC compartment eventually recovered in size, concurrent with accumulation of GCBC that carried unmodified rather than deleted BMPR1A alleles, indicating strong selective pressure to maintain BMPR1A expression .
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Long-term Effects: Despite the selective retention of BMPR1A-expressing cells, there was a permanent marked reduction in:
These findings demonstrate a novel role for BMPR1A in modulating B cell responses and establishing long-term immunological memory, which has significant implications for vaccine development and understanding humoral immunity .
What is the role of BMPR1A in tumor development and progression?
BMPR1A has been implicated in tumor development and progression, with evidence suggesting context-dependent roles:
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Tumor Suppressor Role: Mutations and deletions of BMPR1A are associated with juvenile polyposis syndrome, which predisposes to colorectal and upper gastrointestinal cancer, suggesting a tumor suppressor function in these tissues .
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Myeloid Cell Function: Conditional deletion of BMPR1A in myeloid cells (using LysMCre) restricts tumor progression in syngeneic mouse models, indicating that myeloid BMPR1A expression may promote tumor growth in certain contexts .
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Variable Clinical Manifestations: The clinical phenotype associated with BMPR1A deletions can be variable. For example, one patient with a deletion encompassing BMPR1A was diagnosed with rectal bleeding at age 20, had a partial colectomy at age 21, later had a gastrectomy for gastric polyps at age 54, and then developed rectal cancer at age 55 .
What are the key considerations when using recombinant BMPR1A protein in experimental systems?
When working with recombinant human BMPR1A protein in experimental systems, researchers should consider several important factors:
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Protein Structure: Commercially available recombinant human BMPR1A protein typically consists of specific fragments (e.g., amino acids 187-532) rather than the full-length protein, which may affect certain applications .
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Expression Systems: Baculovirus-infected Sf9 cells have been successfully used to express recombinant BMPR1A with >90% purity, suitable for Western blotting and functional studies .
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Post-translational Modifications: Native BMPR1A is glycosylated, which may affect its function and recognition by antibodies. Researchers should be aware that recombinant proteins may have different glycosylation patterns depending on the expression system used .
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Biological Activity: Recombinant BMPR1A is an active protein that may elicit biological responses in vivo, so it should be handled with appropriate caution .
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Application Suitability: Different recombinant BMPR1A preparations may be optimized for specific applications such as Western blotting or functional studies, and may not be interchangeable across all experimental contexts .
How can researchers effectively evaluate BMPR1A promoter activity and regulation?
To effectively evaluate BMPR1A promoter activity and regulation, researchers have employed several strategies:
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Luciferase Reporter Assays: These have been used to assess wild-type promoter activity and the effects of mutations. Progressive deletion constructs (520 bp, 440 bp, 225 bp, and 120 bp) have helped identify critical regulatory regions .
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Transcription Factor Binding Site Analysis: In silico tools such as MatInspector and Promoter Scan can be used to identify potential binding sites. Important transcription factors for BMPR1A regulation include MZF1, SP-1, E2F, AP-2, and TF2B .
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Site-Directed Mutagenesis: This technique has been used to create specific mutations in the promoter to evaluate their effects on activity. For instance, mutations at positions -224, -306, -328, and -386 have been studied in relation to juvenile polyposis syndrome .
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Cross-Species Comparisons: Analysis of promoter conservation across species (47% orthology to brown rat, 68% to wild boar) can help identify functionally important regulatory elements .
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RACE (Rapid Amplification of cDNA Ends): 5′ RACE from lymphoblastoid cell lines and normal colon tissue has been used to identify non-coding exons and putative promoters of BMPR1A .
What are emerging areas of BMPR1A research with therapeutic potential?
Several promising research directions for BMPR1A have therapeutic potential:
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Cancer Therapeutics: Understanding the tumor suppressor role of BMPR1A in gastrointestinal tissues could lead to new therapeutic approaches for colorectal and upper GI cancers. Particularly, restoring BMPR1A signaling in cases with promoter mutations might be a viable strategy .
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Immunomodulation: Given BMPR1A's role in B cell memory formation and germinal center dynamics, targeting this pathway could enhance vaccine efficacy or modulate autoimmune conditions. The strong selective pressure for retaining BMPR1A expression in B cells underscores its importance in humoral immunity .
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Cardiovascular Applications: The identification of BMPR1A as a candidate gene for congenital heart defects suggests potential applications in cardiac development and repair. Further research into how BMPR1A influences cardiac morphogenesis could inform regenerative medicine approaches .
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Tumor Microenvironment Modulation: The finding that myeloid-specific BMPR1A deletion restricts tumor progression points to potential for targeting BMPR1A in tumor-associated myeloid cells as a therapeutic strategy. This approach might complement conventional cancer treatments by altering the tumor microenvironment .
What methodological challenges remain in BMPR1A research?
Despite significant progress, several methodological challenges remain in BMPR1A research:
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Tissue-Specific Functions: BMPR1A may have different functions and regulatory mechanisms across tissues and developmental stages. Developing experimental systems that can capture this complexity remains challenging .
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Promoter Complexity: The presence of multiple promoters and non-coding exons complicates the study of BMPR1A regulation. More comprehensive approaches are needed to understand how these different regulatory elements interact in various physiological contexts .
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Signaling Pathway Integration: BMPR1A functions within complex signaling networks, interacting with multiple ligands (BMP2, BMP4, GDF5, GDF6) and downstream effectors. Elucidating how these different inputs and outputs are integrated represents a significant challenge .
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Translating Animal Models to Human Applications: While conditional knockout models have provided valuable insights, translating these findings to human therapeutics requires additional validation in human systems and careful consideration of potential side effects given BMPR1A's roles in multiple tissues .
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Long-term Memory Formation: The mechanisms by which BMPR1A influences long-term B cell memory formation are not fully understood. Developing experimental approaches to track memory cells over extended periods and across tissues presents technical challenges .
