To understand why this pathway has attracted such intense scrutiny, it helps to look at its molecular architecture. In its canonical form, NF-κB dimers—most commonly composed of the p65 (RelA) and p50 subunits—sit idle in the cytoplasm, tethered by inhibitory IκB proteins. When pro-inflammatory cytokines such as tumour necrosis factor alpha or interleukin-1 engage their receptors, a signalling cascade triggers the IκB kinase (IKK) complex, whose regulatory NEMO subunit assembles a ubiquitin-dependent signalosome. IKK then phosphorylates IκBα, marking it for proteasomal destruction and freeing NF-κB to enter the nucleus and switch on hundreds of target genes. The non-canonical arm works differently: NF-κB-inducing kinase (NIK) activates an IKKα-dependent process that processes the precursor p100 into p52, generating RelB/p52 dimers that control a distinct set of genes involved in lymphoid organogenesis, immune cell function and, crucially, tumour-microenvironment communication. The review emphasises that these two arms are not isolated modules but a single integrated system, with feedback loops, shared components such as the fourth IκB protein, and cross-regulation that shapes both the timing and the composition of the transcriptional response.

What makes NF-κB particularly treacherous in breast cancer is that its behaviour varies dramatically across molecular subtypes. The review systematically dissects luminal A, luminal B, HER2-enriched and basal-like or triple-negative disease, showing that the magnitude and biological consequences of NF-κB activation are anything but uniform. In hormone receptor-positive tumours, NF-κB engages in intimate crosstalk with the oestrogen receptor alpha. Landmark work cited in the review demonstrated that an IKKα-dependent transcriptional complex is required for oestrogen receptor-mediated gene activation, meaning that the inflammatory pathway is not merely a parallel route to malignancy but is physically embedded in the machinery that oestrogen-responsive tumours depend upon. This entanglement helps explain why NF-κB activity is repeatedly implicated in endocrine therapy resistance: as tumours evolve under the selective pressure of anti-oestrogen drugs, they appear to lean increasingly on inflammatory signalling to maintain survival programmes that the blocked receptor can no longer fully provide.

In HER2-positive disease, the picture shifts toward cooperation with the HER2-PI3K-AKT axis, one of the most consequential growth-factor pathways in this aggressive subtype. Constitutive activation of PI3K-AKT signalling can potentiate NF-κB-dependent transcription, reinforcing anti-apoptotic gene expression and supporting the survival of tumour cells exposed to HER2-targeted agents. The review also highlights experimental evidence that blocking NF-κB can enhance the responsiveness of mammary tumours to JAK inhibitors, suggesting that inflammatory and cytokine signalling pathways converge in ways that single-agent approaches fail to fully exploit. For triple-negative breast cancer—the subtype with the fewest targeted options—NF-κB assumes an even more central role. Studies using small inhibitory RNAs in oestrogen receptor-negative cell lines showed that suppressing the pathway impairs proliferation and survival, while IKK inhibition with compounds such as BMS-345541 has been reported to suppress breast tumorigenesis and metastasis by targeting GD2-positive cancer stem cell populations, the self-renewing cells widely believed to seed relapse and metastatic spread.

Perhaps the most clinically resonant section of the review concerns epithelial-mesenchymal transition, the cellular reprogramming that allows epithelial tumour cells to acquire motility, invasiveness and stem-like properties. NF-κB has been shown to regulate the expression of key EMT genes in breast cancer cells, effectively serving as a transcriptional gatekeeper for the plasticity that underpins metastasis. This connects directly to the inflammatory cytokine network: interleukin-1 signalling through NF-κB has been shown to be required for tumour invasiveness and angiogenesis in experimental models, and endogenous production of interleukin-1 beta by breast cancer cells has been demonstrated to drive metastasis and colonisation of the bone microenvironment in patient-derived systems. In other words, NF-κB does not merely respond to inflammation—it helps tumour cells manufacture their own inflammatory niche, a self-reinforcing loop that promotes dissemination to bone, the most common site of breast cancer metastasis.

The tumour microenvironment adds another layer of complexity. The review devotes substantial attention to macrophage heterogeneity, describing how tumour-associated macrophages can be co-opted by cancer cells to support growth and immune evasion. Recent work on an unconventional p65/p52 NF-κB module in breast tumour-associated macrophages suggests that these infiltrating immune cells use hybrid canonical-non-canonical signalling to regulate genes that shape the microenvironment in the tumour’s favour. Structural biology is beginning to illuminate how different NF-κB dimer compositions read DNA and activate transcription, with high-resolution studies of p52 homodimer-DNA complexes and NMR analyses of NF-κB-DNA interactions rationalising why specific dimer combinations produce distinct transcriptional outcomes. This structural and mechanistic granularity matters therapeutically: if different dimers control different gene programmes in different cellular compartments, then blunt pathway inhibition risks suppressing beneficial immune functions while sparing the tumour-promoting activities clinicians most want to eliminate.

Genotoxic stress introduces yet another dimension. Chemotherapy and radiotherapy work in part by damaging DNA, yet the review describes how the LUBAC ubiquitin ligase complex promotes linear ubiquitination of NEMO in response to genotoxic stress, activating NF-κB precisely when tumour cells are under attack. This damage-induced NF-κB activity can function as a survival shield, upregulating anti-apoptotic genes and helping cells repair or tolerate the damage inflicted by treatment. Consistent with this, proteasome inhibition with bortezomib has been shown to restore apoptotic factors and sensitise breast cancer cells to docetaxel in preclinical models, and clinical trials have tested bortezomib in combination with capecitabine in metastatic disease and with fulvestrant in hormone receptor-positive tumours resistant to aromatase inhibitors. A related strategy exploits SMAC mimetics, which synergise with endocrine therapy to potentiate antigen presentation and tumour regression in hormone receptor-positive breast cancer, in part by disabling NF-κB-dependent survival pathways.

Therapeutically, the review maps out a spectrum of intervention points, each with distinct trade-offs. Upstream inhibition can target receptor-level signals such as RANK/RANKL, which has attracted attention as a potential prevention target in BRCA1-mutation carriers, with a systematic review and meta-analysis now assessing the prognostic value of RANK signalling across breast cancer populations. Proteasome blockade offers a broad but toxic approach; selective NIK inhibitors are advancing as a more precise way to disable the non-canonical arm; and IKK inhibitors aim at the convergence point of both pathways. The authors also highlight emerging precision-delivery strategies and targeted-degradation concepts, including approaches that could eliminate specific NF-κB subunits rather than merely silencing their activity. Yet the review is notably candid about the translational gap: clinical data remain sparse relative to an enormous preclinical literature, and indiscriminate NF-κB inhibition carries real risks, given the pathway’s essential roles in immunity and inflammation.

The overarching message is one of disciplined optimism. NF-κB is neither a universal villain nor an untouchable guardian; it is a context-dependent network whose contribution to breast cancer depends on subtype, dimer composition, cellular compartment and the surrounding microenvironment. The review proposes a framework for subtype- and context-selective targeting, anchored in biomarker-driven patient stratification rather than blanket suppression. If that framework can be validated, the inflammatory switch that breast cancers exploit to survive, spread and resist treatment may finally become the vulnerability that clinicians have been searching for.

Subject of Research: NF-κB signalling mechanisms, crosstalk and therapeutic targeting in breast cancer

Article Title: Nuclear factor κB signalling in breast cancer: mechanisms, crosstalk and therapeutic targeting

Article References: Muthiah, B., Santha Moorthi Rajah, R. R., Kumar, A. S., Srikesavan, S., Chandrasekaran, V. N., & Priya, K. (2026). Nuclear factor κB signalling in breast cancer: mechanisms, crosstalk and therapeutic targeting. Molecular Biology Reports, 53(1), Article 1687. https://doi.org/10.1007/s11033-026-12871-y

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12871-y

Keywords: NF-κB, breast cancer, canonical pathway, non-canonical pathway, IKK, NIK, HER2, triple-negative breast cancer, tumour microenvironment, therapy resistance, EMT, RANK/RANKL

To understand why the finding matters, it helps to revisit how the innate immune system detects bacterial invaders. Immune cells called macrophages patrol tissues armed with pattern recognition receptors, molecular sensors that spot conserved microbial signatures. Among the most potent of these signatures is lipopolysaccharide, or LPS, a component of the outer membrane of Gram-negative bacteria. When bacteria multiply, they shed LPS-rich outer membrane vesicles, tiny blebs of membrane that can travel to distant sites in the body, sneak inside immune cells, and ignite inflammation far from the original infection. This dissemination of inflammatory triggers is a hallmark of systemic inflammatory conditions, sepsis chief among them.

Once intracellular LPS is detected, the cell deploys an inflammasome, a multiprotein machine that acts as both alarm and weapon. Inflammasomes come in two flavors. The canonical pathway relies on well-studied sensors such as NLRP3, while the non-canonical pathway is triggered directly by intracellular LPS through the inflammatory caspase-11 in mice, and caspase-4 and caspase-5 in humans. Activation of either pathway leads caspase-1 to process pro-inflammatory cytokines, most notably interleukin-1 beta, and to cleave Gasdermin-D, the executioner protein that punches holes in the cell membrane and drives inflammatory cell death. While decades of research have mapped how post-translational modifications tune the canonical pathway, the modifications governing the non-canonical route have remained largely mysterious. That gap is precisely where the McGill team, led by Michel L. Tremblay, focused its attention.

The researchers zeroed in on PTPN2, an enzyme that removes phosphate groups from tyrosine residues on target proteins, thereby switching signaling circuits on or off. To probe its role, they generated mice lacking Ptpn2 specifically in myeloid cells, the lineage that includes macrophages, and challenged these animals with LPS-rich outer membrane vesicles and with acute sepsis models. The results were striking. In macrophages deficient in Ptpn2, the transcription of interleukin-1 beta, the flagship cytokine of inflammasome biology, was markedly impaired. The defect traced back to dysregulated signaling through TLR4, the cell-surface LPS receptor, and the p38 MAPK pathway, a cascade that normally drives the priming phase of inflammasome activation by ramping up cytokine gene expression.

Intriguingly, the compromised priming did not translate into wholesale collapse of the inflammasome machinery. Levels of caspase-11, caspase-1, and Gasdermin-D remained unchanged in the knockout cells, indicating that the enzyme’s influence is exerted upstream, at the level of inflammatory gene transcription and signal tuning, rather than by altering the abundance of the core inflammasome components themselves. This distinction is biologically important: it suggests PTPN2 shapes the intensity of the inflammatory output rather than the mere presence of the detonator, a nuance that could matter greatly when designing drugs that target the pathway.

The study also uncovered a novel substrate for PTPN2, adding a fresh branch to the enzyme’s known interaction map. The team found that Lyn, a member of the Src-family of kinases, becomes hyperphosphorylated in the absence of Ptpn2. Because phosphatases and kinases operate in opposing pairs, this observation identifies Lyn as a direct or proximal target whose phosphorylation state PTPN2 normally restrains. Src-family kinases sit at hubs connecting receptor activation to downstream signaling, so their dysregulation in Ptpn2-deficient macrophages provides a mechanistic thread linking the phosphatase to the altered TLR4 and p38 MAPK signaling observed in the knockout animals.

Adding a second layer of complexity, the researchers found that loss of PTPN2 unleashes a STAT1-mediated program that boosts production of nitric oxide, a reactive molecule with a double-edged role in immunity. While nitric oxide can help kill pathogens, the study showed that in this context it undermines inflammasome activity by compromising mitochondrial fitness. Mitochondria are not merely cellular power plants; they supply signals and metabolites that feed inflammasome activation, and their dysfunction can blunt the cell’s inflammatory capacity. In Ptpn2-deficient macrophages, therefore, excessive nitric oxide erodes the very organelles the inflammasome depends upon, further dampening the response.

The in vivo consequences of these cellular defects became clear when the mice were subjected to acute sepsis. Animals lacking Ptpn2 in myeloid cells exhibited reduced numbers of small peritoneal macrophages, a key resident immune population, and lower serum levels of interleukin-1 beta following the septic challenge. Together, these findings indicate a dampened pro-inflammatory response in the absence of the phosphatase. In the context of sepsis, where excessive inflammation drives organ damage and death, a blunted response might at first glance seem protective. But the picture is nuanced: interleukin-1 beta also mobilizes host defenses, and the reduced macrophage population suggests that PTPN2 supports aspects of immune competence as well as inflammation. The enzyme, in other words, is not simply a brake or an accelerator but a fine-tuner of the response.

That dual role is what makes PTPN2 an attractive therapeutic candidate. Phosphatases were long considered undruggable, but recent advances in medicinal chemistry have brought PTPN2 inhibitors into clinical consideration, particularly in oncology, where the enzyme’s effects on T cells and tumor immunity have drawn intense interest. The McGill study adds a new dimension to that conversation: in sepsis and systemic inflammation, modulating PTPN2 activity could, in principle, recalibrate the non-canonical inflammasome axis and the cytokine output that fuels inflammatory injury. The authors highlight this potential, positioning the enzyme as a target for managing systemic inflammation. Any such strategy would need to account for the pathway’s complexity, since the same enzyme that supports cytokine production also, through its restraint of STAT1 and nitric oxide, protects mitochondrial fitness and inflammasome function.

The work also carries broader conceptual weight for immunology. By demonstrating that a tyrosine phosphatase governs the non-canonical inflammasome pathway, the study establishes that this arm of innate immunity, often treated as a parallel, LPS-triggered circuit, is subject to the same intricate layers of post-translational regulation that shape its canonical counterpart. It connects outer membrane vesicle biology, TLR4 signaling, Src-family kinase activity, STAT1 activation, mitochondrial health, and cytokine secretion into a single regulatory network centered on one enzyme. For clinicians confronting sepsis, a syndrome that kills millions each year and for which treatment remains largely supportive, the identification of a tunable node in the inflammatory circuitry offers a genuine reason for optimism. For basic researchers, it opens a set of new questions: how PTPN2 is itself regulated during infection, whether the Lyn and STAT1 branches operate independently, and whether human patients with altered PTPN2 activity show different sepsis trajectories. The answers could shape the next generation of anti-inflammatory therapies.

Subject of Research: Role of the phosphatase PTPN2 in regulating non-canonical inflammasome activation and inflammatory responses in sepsis

Article Title: PTPN2 sustains non-canonical inflammasome activation and shapes the inflammatory response to sepsis

Article References: Colalillo, B., Aubry, I., Aumont, P., Poirier, A. J., Hincapie, A. M., Wu, C., St-Laurent, E., Martinez Cordova, Z., & Tremblay, M. L. (2026). PTPN2 sustains non-canonical inflammasome activation and shapes the inflammatory response to sepsis. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06469-7

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06469-7

Keywords: PTPN2, sepsis, inflammasome, non-canonical pathway, interleukin-1 beta, LPS, macrophages, TLR4, p38 MAPK, Lyn kinase, STAT1, nitric oxide