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Updated: Jun 29, 2026
Myeloid Innate Signaling Pathway Regulation by MALT1 Paracaspase Activity
Published on: January 7, 2019
SHIP blocks (MDP + LPS)-induced synergy in macrophages independent of catalytic activity
Yvonne C F Pang1, Susan C Menzies1, Laura M Sly1
1Department of Pediatrics, Division of Gastroenterology, BC Children's Hospital and the University of British Columbia, Room A5-142, BC Children's Hospital Research Institute, 950 West 28th Avenue, Vancouver, BC V5Z 4H4, Canada.
Abstract:
Macrophages coordinate cytokine responses by integrating signals from pattern recognition receptors including NOD2 and TLR4. NOD2 detects muramyl dipeptide derived from bacterial peptidoglycan, and TLR4 recognizes lipopolysaccharide in the outer membrane of Gram-negative bacteria. NOD2 and TLR4 signals synergize to enhance cytokine production in myeloid cells. While synergy can support host defense, it must be regulated to minimize the risk of excessive inflammation. The lipid phosphatase SHIP, a negative regulator of Class I PI3Ks, reduces inflammatory signaling, but its role during NOD2-TLR4 co-stimulation remains undefined. We found that SHIP limits IL-1β production by blocking synergy in bone marrow-derived macrophages co-stimulated with muramyl dipeptide and lipopolysaccharide. SHIP-/- macrophages showed a synergistic increase in IL-1β that was not evident in SHIP+/+ macrophages. Moreover, reducing SHIP protein concentrations by differentiation in different growth factors, IL-4 treatment, or siRNAs enabled synergy for IL-1β production in SHIP+/+ macrophages. Pharmacologic inhibition of SHIP's catalytic activity did not promote synergy, and similarly, blocking PI3K had no effect, suggesting that the response is independent of SHIP's phosphatase activity. Synergy for IL-1β production was dependent on NOD2 signaling despite NOD2 stimulation alone resulting in little to no IL-1β. Moreover, IL-1β was selectively enhanced in SHIP-/- macrophages during co-stimulation with MDP and LPS, or when MDP stimulation preceded LPS. These findings identify SHIP's adaptor function as a negative regulator of IL-1β induced by NOD2-TLR4 co-stimulation in macrophages, and suggest that SHIP acts as a gatekeeper for macrophage IL-1β during early innate immune activation.
Insights
The lipid phosphatase SHIP negatively regulates synergistic IL-1β production by macrophages responding to bacterial NOD2 and LPS TLR4 signals. SHIP acts as a gatekeeper, preventing excessive inflammation during innate immune activation.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages utilize pattern recognition receptors like NOD2 and TLR4 to detect microbial components.
- NOD2 recognizes muramyl dipeptide (MDP) from peptidoglycan, while TLR4 detects lipopolysaccharide (LPS).
- Co-stimulation via NOD2 and TLR4 synergistically enhances cytokine production, crucial for host defense but requiring regulation to prevent excessive inflammation.
Purpose of the Study:
- To investigate the role of the lipid phosphatase SHIP in regulating synergistic cytokine production during NOD2 and TLR4 co-stimulation.
- To determine if SHIP influences IL-1β production in response to combined MDP and LPS stimulation in macrophages.
Main Methods:
- Utilized bone marrow-derived macrophages from SHIP-/- and SHIP+/+ mice.
- Co-stimulated macrophages with MDP and LPS to assess synergistic IL-1β production.
- Manipulated SHIP protein levels using differentiation factors, IL-4, and siRNAs.
- Investigated the role of SHIP's phosphatase activity by pharmacologic inhibition of SHIP and PI3K.
Main Results:
- SHIP-/- macrophages exhibited synergistic IL-1β production upon co-stimulation, unlike SHIP+/+ macrophages.
- Reduced SHIP levels in SHIP+/+ macrophages enabled synergistic IL-1β production.
- Synergy for IL-1β was dependent on NOD2 signaling and independent of SHIP's phosphatase activity or PI3K.
- SHIP acts as an adaptor protein, negatively regulating IL-1β induced by NOD2-TLR4 co-stimulation.
Conclusions:
- SHIP functions as a critical negative regulator of synergistic IL-1β production in macrophages during combined NOD2 and TLR4 activation.
- SHIP's adaptor function, not its phosphatase activity, is key to controlling IL-1β responses.
- SHIP acts as a gatekeeper, preventing excessive IL-1β release and potential inflammation in early innate immune responses.
