Phospho-RIPK2 (S176) Antibody

What is RIPK2 and why is its phosphorylation at Serine 176 significant?

RIPK2 (Receptor-interacting serine/threonine protein kinase 2) is a member of the receptor-interacting protein (RIP) family of serine/threonine protein kinases. It contains a C-terminal caspase activation and recruitment domain (CARD) and functions as a critical component of signaling complexes in both innate and adaptive immune pathways. RIPK2 serves as a potent activator of NF-kappaB and can induce apoptosis in response to various stimuli .

Phosphorylation of RIPK2 at Serine 176 is particularly significant because it represents a crucial activation mechanism. Recent research demonstrates that phosphorylation at this specific site (S176) is essential for activating downstream NF-κB and MAPK signaling pathways . Unlike phosphorylation at other sites (S531 and Y381), S176 phosphorylation status directly correlates with inflammatory pathway activation and appears to be a regulatory node that can be modulated in various disease states, including osteoarthritis .

What applications and techniques can be used with Phospho-RIPK2 (S176) Antibody?

Phospho-RIPK2 (S176) Antibody can be employed in multiple experimental techniques:

The antibody is particularly valuable for monitoring changes in RIPK2 activation status during signaling events. It can be used to assess RIPK2 activity in various experimental contexts, including inflammatory stimulation, genetic manipulation of upstream regulators, and disease models .

How should Phospho-RIPK2 (S176) Antibody samples be prepared and stored for optimal results?

For optimal results when working with Phospho-RIPK2 (S176) Antibody:

• Storage conditions: Store at -20°C in aliquots to avoid repeated freeze-thaw cycles that may compromise antibody activity .

• Buffer composition: The antibody is typically provided in PBS without Mg²⁺ and Ca²⁺, containing 150 mM NaCl, pH 7.4, with 50% glycerol and 0.02% sodium azide as preservatives .

• Sample preparation: When detecting phosphorylated proteins, samples should be prepared with phosphatase inhibitors to prevent dephosphorylation during processing.

• Positive controls: Include IL-1β-stimulated cell lysates as positive controls, as this treatment has been shown to increase RIPK2 S176 phosphorylation .

• Working dilution: The optimal working dilution should be determined experimentally for each application, but manufacturer recommendations provide a starting point .

How does RIPK2 S176 phosphorylation regulate NF-κB and MAPK signaling pathways?

RIPK2 S176 phosphorylation serves as a critical molecular switch for activating downstream inflammatory signaling cascades. Research using phosphomimetic mutations provides compelling evidence for its mechanistic importance:

When S176 is mutated to aspartate (S176D) to mimic sustained phosphorylation, there is marked enhancement of NF-κB and MAPK signaling pathways. This is evidenced by elevated levels of phosphorylated signaling components including:

• p-IKKα/β

• p-P65

• p-IKBα

• p-JNK

• p-ERK

• p-P38

Conversely, when S176 is mutated to alanine (S176A) to prevent phosphorylation, there is significant reduction in the activation of these pathways . This bidirectional experimental approach confirms that S176 phosphorylation is not merely associated with but essential for RIPK2-mediated inflammatory signaling.

Importantly, the phosphorylation status of RIPK2 at S176 also correlates with its ubiquitination levels, with higher phosphorylation associated with increased ubiquitination . This suggests a coordinated post-translational modification mechanism controlling RIPK2 activity.

What is the relationship between RIPK2 function and NOD/TLR signaling pathways?

RIPK2 functions differently in NOD2 versus TLR4 signaling pathways, which has significant implications for understanding inflammatory mechanisms:

In microglial cells, RIPK2 degradation using a specific PROTAC molecule (GSK3728857A) completely abolished muramyl dipeptide (MDP)-induced inflammatory responses. MDP is a NOD2 agonist, and this abolishment included:

• Prevention of increases in iNOS and COX-2 protein levels

• Inhibition of pro-inflammatory gene transcription

In contrast, RIPK2 degradation only partially attenuated lipopolysaccharide (LPS)-induced inflammatory responses. LPS is a TLR4 agonist, and RIPK2 degradation:

• Partly reduced transcription of some inflammatory genes (Ptgs2, Il-1β, Il6, Ccl2, Mmp9)

• Had no significant effect on Nos2 and Tnfα expression

• Did not attenuate LPS-induced phosphorylation of NF-κB p65 and MAPK p38

This differential requirement for RIPK2 helps resolve the controversy about whether RIPK2 contributes to NOD signaling, TLR signaling, or both. The evidence suggests RIPK2 is crucial for NOD2-mediated responses but plays a more limited role in TLR4 signaling.

How is RIPK2 S176 phosphorylation implicated in osteoarthritis pathology?

Recent research has revealed a significant connection between RIPK2 S176 phosphorylation and osteoarthritis (OA) development:

Immunohistochemical analyses show that p-RIPK2 S176 positive cells are more numerous in:

• Destabilization of the medial meniscus (DMM) surgical models of OA

• Mysm1-conditional knockout mice

• Cartilage samples from human OA patients

The protein MYSM1 appears to attenuate OA progression by recruiting protein phosphatase 2A (PP2A) to dephosphorylate RIPK2 at S176, thereby interrupting the NOD inflammatory pathway . This suggests a potential therapeutic approach through modulation of RIPK2 phosphorylation.

The mechanistic pathway involves:

• MYSM1 binding to Ppp2ca (PP2Ac), a serine/threonine protein phosphatase

• This complex dephosphorylating RIPK2 at S176

• Reduced RIPK2 S176 phosphorylation leading to decreased ubiquitination

• Decreased activation of downstream inflammatory pathways

These findings position RIPK2 S176 phosphorylation as a potential therapeutic target in osteoarthritis management.

What experimental strategies can be used to manipulate RIPK2 phosphorylation?

Several experimental approaches have been documented for manipulating RIPK2 phosphorylation to study its function:

• Plasmid-based mutation strategies:

  • Serine to Aspartate mutation (S176D) to mimic constitutive phosphorylation

  • Serine to Alanine mutation (S176A) to prevent phosphorylation

• Transfection protocols:
  For chondrocytes or 293T cells:

  • 1 μg plasmid

  • 5 μL Lipofectamine 3000

  • 250 μL Opti-MEM

  • 2 mL complete medium

  • 48-hour incubation before harvesting

• siRNA knockdown approach:
  For targeting mouse Mysm1 or Ripk2:

  • 50 pmol/L siRNA

  • 5 μL Lipofectamine 3000

  • 250 μL Opti-MEM

  • 2 mL complete medium

• Proteolysis targeting chimera (PROTAC):

  • GSK3728857A has been shown to induce dramatic degradation of RIPK2 in a concentration- and time-dependent manner

  • This approach allows for targeted protein degradation rather than just inhibition

• Stimulation with inflammatory mediators:

  • IL-1β treatment increases RIPK2 S176 phosphorylation

  • MG132 (proteasome inhibitor) can be used alongside to detect ubiquitination

These approaches provide complementary methods to investigate the role of RIPK2 phosphorylation in different experimental contexts.

How can researchers effectively detect and quantify RIPK2 S176 phosphorylation?

To accurately detect and quantify RIPK2 S176 phosphorylation:

• Antibody selection:

  • Use specific phospho-RIPK2 (S176) antibodies that detect endogenous levels of RIPK2 only when phosphorylated at serine 176

  • Ensure the antibody has been validated for your species of interest (human, mouse, rat)

• Western blotting optimization:

  • Use recommended dilutions (1:500-1:3000)

  • Include phosphatase inhibitors in lysis buffers

  • Run parallel blots for total RIPK2 to calculate phosphorylation/total ratio

  • Consider using MG132 for ubiquitination studies

• Immunohistochemistry/Immunofluorescence:

  • Use recommended dilutions (1:50-1:100)

  • Counterstain for cell identification

  • Quantify positive cells as a percentage of total cells

• Controls:

  • Positive controls: IL-1β-stimulated samples

  • Negative controls: RIPK2 knockdown or S176A mutants

  • Specificity controls: competing peptide blocking

• Quantification approaches:

  • Densitometric analysis of western blots

  • Count of positive cells in IHC/IF

  • Normalization to housekeeping proteins or total RIPK2

These methodologies ensure reliable and reproducible measurement of RIPK2 S176 phosphorylation in various experimental settings.

What are the critical considerations when interpreting contradictory findings about RIPK2?

When faced with seemingly contradictory results regarding RIPK2 function:

• Cell type specificity:

  • RIPK2 may function differently in various cell types (e.g., chondrocytes vs. microglia)

  • Always consider the cellular context when interpreting results

• Stimulus specificity:

  • RIPK2 has different roles in NOD2 versus TLR4 signaling

  • The inflammatory stimulus used (MDP vs. LPS) significantly impacts RIPK2's role

• Experimental approach limitations:

  • Genetic knockout versus acute protein degradation (PROTAC) may yield different results

  • Phosphomimetic mutations (S176D) may not perfectly recapitulate physiological phosphorylation

• Temporal considerations:

  • Acute versus chronic RIPK2 activation may engage different downstream pathways

  • Time-course experiments are critical for understanding the dynamics of RIPK2 signaling

• Pathway crosstalk:

  • RIPK2 interacts with multiple signaling pathways (NF-κB, MAPK)

  • Compensatory mechanisms may mask phenotypes in some experimental settings

Understanding these factors helps reconcile apparently contradictory findings in the literature and highlights the complex, context-dependent role of RIPK2 in inflammatory signaling.

How do post-translational modifications interact to regulate RIPK2 activity?

Recent research reveals a complex interplay between phosphorylation and ubiquitination in regulating RIPK2 function:

RIPK2 S176 phosphorylation status correlates directly with its ubiquitination levels, with experimental evidence showing:

• Enhanced total protein and RIPK2 ubiquitination levels accompany increased pS176 levels following IL-1β exposure

• MYSM1 overexpression reduces both RIPK2 ubiquitination and p-RIPK2 S176 levels induced by IL-1β

• Reduction of RIPK2 phosphorylation by S176A mutation exhibits lower levels of RIPK2 ubiquitination

This suggests a coordinated regulation mechanism where:

• Phosphorylation at S176 precedes and may facilitate ubiquitination

• Deubiquitinating enzymes like MYSM1 may indirectly affect phosphorylation status

• Both modifications together regulate RIPK2's ability to activate downstream signaling

Understanding this interplay may provide new opportunities for therapeutic intervention by targeting either phosphorylation or ubiquitination machinery.

What potential therapeutic approaches might target RIPK2 S176 phosphorylation?

Based on current research, several therapeutic strategies targeting RIPK2 S176 phosphorylation show promise:

• Phosphatase recruitment:

  • The MYSM1-PP2A complex dephosphorylates RIPK2 at S176

  • Molecules that enhance this interaction could reduce inflammatory signaling

• Direct kinase inhibition:

  • Identifying and inhibiting the kinase responsible for S176 phosphorylation

  • Development of site-specific inhibitors that prevent only S176 phosphorylation

• Targeted protein degradation:

  • PROTAC approaches like GSK3728857A that induce RIPK2 degradation

  • This strategy has shown complete abolishment of MDP-induced inflammatory responses

• Peptide-based interventions:

  • Peptides mimicking the S176 region could compete for kinase binding

  • Cell-penetrating peptides could deliver phosphorylation-blocking agents

• Genetic approaches:

  • CRISPR-based modification of S176 to prevent phosphorylation in disease models

  • RNA interference targeting RIPK2 expression in specific tissues

These approaches highlight potential therapeutic avenues for conditions where RIPK2-mediated inflammation plays a pathological role, such as osteoarthritis and neurodegenerative conditions.