Recombinant Human Peptidyl-prolyl cis-trans isomerase FKBP11 (FKBP11)

What is the structure and function of human FKBP11?

FKBP11 (also known as FKBP19, FK506-binding protein 11) is a 19 kDa protein belonging to the FKBP-type PPIase family. It contains a cleavable N-terminal signal sequence followed by a putative PPIase domain with homology to FKBP12 . As a peptidyl-prolyl cis-trans isomerase, FKBP11 catalyzes the slow cis-trans isomerization of peptidyl-prolyl bonds, thereby facilitating protein folding during protein synthesis . FKBP11 is primarily localized to the endoplasmic reticulum membrane as an integral membrane protein . Its PPIase activity, like other FKBP family members, is inhibited by immunosuppressant compounds including FK506 and rapamycin .

How is recombinant human FKBP11 typically produced for research use?

Recombinant human FKBP11 can be produced using various expression systems. A common approach involves expressing the protein (amino acids 1-155) as an Fc chimera in HEK 293 cells, which yields high purity (>90%) protein with low endotoxin levels (<1 EU/μg) . This expression system enables proper folding and potential post-translational modifications relevant to the human protein. Alternative approaches include cell-free expression systems for producing transmembrane FKBP11 protein . The recombinant protein produced is suitable for applications such as SDS-PAGE analysis, functional studies, and as a standard in quantification assays.

What tissues demonstrate significant FKBP11 expression?

FKBP11 mRNA is abundantly expressed in multiple secretory tissues, including the pancreas, stomach, and salivary glands . This tissue distribution pattern suggests FKBP11 may play specialized roles in secretory cells where protein folding demands are high. Additionally, FKBP11 expression is often increased in inflammatory tissues, as observed in patients with Crohn's disease . Research also indicates elevated expression in various pathological conditions including hepatocellular carcinoma and osteosarcoma tissues compared to normal counterparts .

How does FKBP11 contribute to inflammation through NF-κB pathway interaction?

FKBP11 has been demonstrated to provoke inflammation in endothelial cells through direct interaction with the NF-κB p65 subunit . This interaction results in enhanced production of pro-inflammatory cytokines. In experimental models of acute aortic dissection (AAD), FKBP11 overexpression in endothelium facilitates transendothelial migration of circulating monocytes into the aorta . These monocytes subsequently differentiate into active macrophages, secreting matrix metalloproteinases (MMPs) and other extracellular matrix degrading proteins, which contribute to sustained inflammation and disease progression.
Mechanistically, angiotensin II treatment induces FKBP11 expression in endothelial cells, promoting nuclear localization of phosphorylated p65 (NF-κB subunit). siRNA-mediated knockdown of FKBP11 effectively suppresses this angiotensin II-induced p65 activation and significantly reduces monocyte transmigration through endothelial monolayers . These findings establish FKBP11 as a key regulator in inflammation through NF-κB-dependent pathways.

What is the role of FKBP11 in endoplasmic reticulum (ER) stress and the unfolded protein response?

FKBP11 serves as an integral component in the cellular response to ER stress and the unfolded protein response (UPR). Research demonstrates that FKBP11 expression increases during ER stress conditions, suggesting its involvement in protein folding quality control mechanisms . In models of 2,4,6-trinitrobenzenesulphonic acid-induced mouse colitis, overexpression of FKBP11 correlates with increased expression of the ER stress marker 78 kDa glucose-regulated protein in colon tissues .
In intestinal epithelial cells (IECs) stimulated with interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α)—an established model for ER stress and apoptosis—FKBP11 overexpression significantly attenuates the elevated expression of pro-apoptotic proteins including Bcl2-associated X apoptosis regulator, caspase-12, and active caspase-3 . Furthermore, FKBP11 suppresses the phosphorylation of c-Jun N-terminal kinase (JNK) and decreases apoptosis in IFN-γ/TNF-α stimulated IECs . These findings suggest FKBP11 plays a protective role against ER stress-induced apoptosis by inhibiting the ER stress-associated JNK/caspase apoptotic pathway.

How does FKBP11 influence the pathogenesis of various diseases?

FKBP11 has been implicated in multiple disease states through its roles in protein folding, ER stress response, and inflammatory processes:

• Crohn's Disease (CD): Increased FKBP11 expression has been detected in intestinal inflammatory tissues from CD patients. Evidence suggests FKBP11 protects intestinal epithelial cells against inflammation-induced apoptosis by inhibiting ER stress-associated pathways .

• Hepatocellular Carcinoma (HCC): Progressive elevation of FKBP11 expression during HCC development has been observed, suggesting FKBP11 may serve as a potential early marker for HCC .

• Osteosarcoma: FKBP11 has been identified as improving the malignant property of osteosarcoma cells and functioning as a prognostic factor .

• Acute Aortic Dissection (AAD): FKBP11 is strongly expressed in endothelial cells of AAD patients. It interacts with NF-κB p65 subunit to induce pro-inflammatory cytokines, facilitating monocyte transmigration and contributing to sustained inflammation .

• Other Inflammatory Conditions: FKBP11 has also been implicated in type 2 diabetes, systemic lupus erythematosus, and hepatitis, suggesting a broader role in ER stress-associated inflammatory diseases .

What are the optimal methods for detecting FKBP11 expression in tissue samples?

For comprehensive analysis of FKBP11 expression in tissue samples, a multi-method approach is recommended:

• qRT-PCR: For quantitative analysis of FKBP11 mRNA expression. Design primers specific to FKBP11, avoiding regions of homology with other FKBP family members. Use appropriate housekeeping genes (e.g., GAPDH, β-actin) for normalization .

• Western Blotting: For protein expression analysis, use whole tissue lysates with antibodies specific to FKBP11. Expected molecular weight is approximately 19 kDa. Include positive controls such as recombinant FKBP11 protein .

• Immunohistochemistry (IHC): For localization studies in paraffin-embedded tissue sections. This method allows visualization of FKBP11 distribution within tissues. Use HRP-DAB reaction (brown) with hematoxylin counterstain (blue) for contrast .

• Double Immunofluorescent Staining: For co-localization studies, combine FKBP11 staining (red) with cell-specific markers such as CD31 (endothelial cells), α-SMA (smooth muscle cells), or Mac-2 (macrophages), along with nuclear staining using DAPI (blue) .
  In disease-specific contexts, such as aortic tissue from AAD patients, FKBP11 expression is prominently observed in the endothelium, which can be confirmed through co-localization with CD31 .

How can researchers effectively modulate FKBP11 expression for functional studies?

For manipulating FKBP11 expression in experimental settings, several approaches have demonstrated efficacy:

• siRNA-Mediated Knockdown:

  • Use specific siRNAs targeting FKBP11 mRNA. Validation studies show that not all siRNAs are equally effective; for example, FKBP11-Si2 and FKBP11-Si3 effectively suppress protein expression while FKBP11-Si1 may not .

  • Transfect cells using standard lipid-based transfection reagents and confirm knockdown efficiency through western blotting and qRT-PCR.

  • Include appropriate scrambled siRNA controls (e.g., NC-Si) .

• Overexpression Systems:

  • Construct expression vectors containing the full human FKBP11 coding sequence.

  • For in vitro studies, transfect cell lines relevant to the disease context (e.g., intestinal epithelial cells for CD studies, endothelial cells for vascular studies).

  • Validate overexpression through western blotting and functional readouts .

• Inducible Systems for Temporal Control:

  • Use doxycycline-inducible or similar systems to achieve temporal control over FKBP11 expression.

  • This approach is particularly useful for studying time-dependent effects in chronic disease models.

• Stimulation with Biological Inducers:

  • Angiotensin II treatment has been demonstrated to induce FKBP11 expression in endothelial cells .

  • IFN-γ/TNF-α combination can be used to create ER stress conditions where FKBP11's protective effects can be studied .

What cell models are most suitable for studying FKBP11 function in different disease contexts?

Based on the literature, several cell models have proven valuable for investigating FKBP11 in disease-specific contexts:

• Intestinal Epithelial Cells (IECs):

  • Suitable for studying FKBP11's role in intestinal inflammation and Crohn's disease.

  • Can be stimulated with IFN-γ/TNF-α to induce ER stress and apoptosis, creating a model where FKBP11's protective effects can be observed .

• Endothelial Cells:

  • EA.hy926 cells have been successfully used to study FKBP11's role in vascular inflammation.

  • Angiotensin II treatment of these cells induces FKBP11 expression and activates NF-κB signaling .

  • These models are particularly relevant for studying vascular conditions like acute aortic dissection.

• Osteosarcoma Cell Lines:

  • For investigating FKBP11's role in bone cancer progression and as a potential prognostic marker .

• Hepatocytes and Liver Cancer Cells:

  • Appropriate for studying FKBP11's involvement in hepatitis and hepatocellular carcinoma development .
    When selecting cell models, consideration should be given to the endogenous expression levels of FKBP11 and the specific signaling pathways being investigated.

How can weighted gene co-expression network analysis be applied to investigate FKBP11's role in disease?

Weighted gene co-expression network analysis (WGCNA) has proven effective in identifying FKBP11 as a key regulator in disease contexts, particularly in acute aortic dissection . For researchers interested in applying this approach:

• Data Collection:

  • Obtain gene expression profiles from disease-relevant tissues (e.g., dissected aorta vs. healthy controls).

  • Use microarray or RNA-sequencing platforms for comprehensive transcriptome profiling.

• Network Construction:

  • Apply WGCNA methodology to identify gene modules (clusters of co-expressed genes) associated with the disease phenotype.

  • Calculate module eigengenes (the first principal component of each module) to represent the expression profile of each module.

• Module-Trait Relationship Analysis:

  • Correlate module eigengenes with clinical traits to identify disease-relevant modules.

  • In AAD research, this approach successfully identified modules containing FKBP11 as significantly associated with the disease .

• Hub Gene Identification:

  • Identify hub genes within significant modules based on intramodular connectivity.

  • Validate candidates (like FKBP11) using independent sample sets through qRT-PCR.

• Functional Validation:

  • After identifying FKBP11 as a candidate hub gene, validate its functional relevance through in vitro and ex vivo experiments.

  • This might include protein expression analysis in patient samples, cell culture studies with gene knockdown/overexpression, and mechanistic investigations .
    This approach provides a comprehensive framework for discovering disease-relevant genes and has successfully highlighted FKBP11's importance in various pathological contexts.

What criteria should be used to evaluate the quality of recombinant FKBP11 for experimental use?

When evaluating recombinant FKBP11 for research applications, consider these quality parameters:

• Purity Assessment:

  • SDS-PAGE analysis should confirm >90% purity, as typically reported for commercial recombinant FKBP11 .

  • Multiple bands or smearing may indicate degradation or contamination with host cell proteins.

• Endotoxin Testing:

  • Endotoxin levels should be quantified and maintained below 1 EU/μg to prevent confounding inflammatory responses in experiments .

  • This is particularly critical for studies investigating FKBP11's role in inflammation.

• Biological Activity:

  • PPIase activity assays should confirm the protein's enzymatic function.

  • The inhibition of this activity by FK506 or rapamycin can serve as a positive control .

• Proper Folding:

  • Circular dichroism spectroscopy can evaluate secondary structure integrity.

  • Thermal shift assays may assess protein stability and proper folding.

• Post-translational Modifications:

  • Mass spectrometry analysis should confirm the expected molecular weight and identify any post-translational modifications relevant to function.

• Expression System Considerations:

  • Human cell lines like HEK 293 are preferred for producing recombinant human FKBP11 to ensure proper folding and modifications .

  • For transmembrane versions, cell-free expression systems may offer advantages for maintaining native conformation .

How can FKBP11 be targeted therapeutically in inflammatory diseases?

Based on FKBP11's role in inflammation and disease pathogenesis, several therapeutic targeting strategies can be considered:

• Small Molecule Inhibitors:

  • Develop specific FKBP11 inhibitors that target its PPIase activity without affecting other FKBP family members.

  • This approach would require high-affinity ligands with selectivity between close homologs, which are currently scarce for FKBP proteins .

  • Unlike the existing FKBP ligands FK506 and rapamycin, ideal candidates would lack immunosuppressive properties while maintaining FKBP11 inhibition .

• Disruption of Protein-Protein Interactions:

  • Target the interaction between FKBP11 and NF-κB p65 subunit to mitigate inflammatory responses.

  • This approach could potentially reduce pro-inflammatory cytokine production without affecting other FKBP11 functions .

• siRNA/Antisense Therapeutics:

  • Develop siRNA or antisense oligonucleotides for targeted knockdown of FKBP11.

  • In vitro evidence suggests that FKBP11 knockdown effectively suppresses angiotensin II-induced monocyte transmigration through endothelial monolayers, supporting the potential efficacy of this approach .

• Cell-Type Specific Targeting:

  • Since FKBP11 shows cell-type specific expression patterns (e.g., endothelial cells in AAD), develop delivery strategies that target specific cell populations.

  • In vascular diseases like AAD, endothelial-targeted delivery systems could enhance therapeutic efficacy while reducing off-target effects .

What is the significance of FKBP11 as a prognostic biomarker in cancer and inflammatory diseases?

FKBP11 demonstrates significant potential as a prognostic biomarker across multiple disease contexts:

How does FKBP11 function differ from other FKBP family members in disease contexts?

While FKBP family members share structural similarities and PPIase activity, FKBP11 demonstrates distinct functional characteristics in disease contexts:

• Subcellular Localization:

  • FKBP11 is primarily localized to the endoplasmic reticulum membrane as an integral membrane protein .

  • This localization is distinct from cytosolic FKBPs like FKBP12 and contributes to FKBP11's specialized role in ER stress responses.

• Tissue Distribution:

  • FKBP11 mRNA is abundant in secretory tissues (pancreas, stomach, salivary glands) .

  • This distribution pattern differs from more ubiquitously expressed FKBPs and suggests tissue-specific functions.

• Response to ER Stress:

  • Unlike some FKBP family members, FKBP11 is specifically involved in the unfolded protein response (UPR) and ER stress pathways .

  • In hepatic steatosis models, FKBP11 functions as a downstream molecule of the classical UPR transducer IRE1α that promotes viable protein folding .

• Inflammatory Regulation:

  • FKBP11 uniquely interacts with the NF-κB p65 subunit to regulate inflammatory responses .

  • This specific interaction is not prominently reported for other FKBP family members.

• Disease Associations:

  • While FKBP51 has been linked to neuropsychiatric disorders and FKBP12 to cardiovascular conditions, FKBP11 shows distinct associations with inflammatory bowel disease, hepatocellular carcinoma, and acute aortic dissection .
    Understanding these functional differences is crucial for developing specific therapeutic interventions targeting FKBP11 without affecting other family members. The binding domain of FKBPs differs only in a few amino acid residues, making the development of selective inhibitors challenging but potentially valuable for targeted disease interventions .