The Challenge of "Cold" Tumors in Immunotherapy

Immune checkpoint therapies (ICT) have revolutionized oncology, but their success has been uneven. Prostate cancer (PCa) stands as a stark example of this disparity. Characterized as an immunologically "cold" tumor, PCa features a profoundly immunosuppressive tumor microenvironment (TME) with scarce T-cell infiltration, rendering it largely unresponsive to current ICT strategies. A central question for the field has been to decipher the precise molecular mechanisms that establish and maintain this immune-resistant state, with the ultimate goal of converting these "cold" tumors into "hot" ones that are susceptible to immunotherapy.

The transcription factor Yin Yang 1 (YY1) has gradually emerged as a key player in this process. Early research established YY1's broad role in immune cell development [4]. More specific studies later linked YY1 to cancer immune evasion by showing it could regulate the expression of the PD-L1 checkpoint protein [3]. A pivotal 2023 study further sharpened this focus, revealing that YY1 promotes M2 macrophage polarization and prostate cancer progression by upregulating IL-6 [2]. Yet, a critical piece of the puzzle was missing: how does the unique, oxygen-deprived (hypoxic) environment within solid tumors specifically leverage YY1 to orchestrate immunosuppression? A recent paper in Nature Communications by Li et al. provides a groundbreaking answer [1].

A Phase Separation Cascade that Stabilizes HIF-1α

The study by Li et al. offers a masterclass in mechanistic biology, connecting environmental stress to a cascade of molecular events that culminates in immune suppression. The researchers began by using imaging mass cytometry on human PCa tissues, making a crucial spatial observation: immunosuppressive, YY1-positive tumor-associated macrophages (TAMs) were not randomly distributed but were specifically enriched in the hypoxic core of the tumors, marked by high levels of HIF-1α.

This finding prompted a deep dive into the underlying molecular choreography within these TAMs:

1. Hypoxia as the Trigger: The investigation revealed that hypoxia acts as the initial trigger. It induces the tyrosine phosphorylation of YY1, a post-translational modification that dramatically alters its biophysical properties.
2. YY1 Phase Separation: This phosphorylation event causes YY1 to undergo liquid-liquid phase separation (LLPS), forming distinct, dot-like condensates within the macrophage nucleus. These condensates effectively act as dynamic, self-organizing molecular hubs.
3. Recruitment of NUSAP1: The YY1 condensates serve as scaffolds to recruit a key partner protein: Nucleolar and Spindle Associated Protein 1 (NUSAP1).
4. HIF-1α SUMOylation and Stabilization: The YY1-NUSAP1 complex is the critical effector. NUSAP1 functions as a SUMO E3 ligase, promoting the SUMOylation of HIF-1α—the master transcriptional regulator of the cellular response to hypoxia. This SUMOylation is the key to HIF-1α's stability; it protects HIF-1α from being targeted for degradation via the ubiquitin-proteasome pathway. Furthermore, SUMOylation itself induces HIF-1α to undergo its own phase separation, further stabilizing the protein and amplifying its downstream signaling.

In essence, the study uncovered a sophisticated "phase separation cascade" where hypoxia initiates a chain reaction of protein modifications and condensations (YY1 → NUSAP1 → HIF-1α) that shields HIF-1α from destruction, thereby locking the TAM into an immunosuppressive state.

From Mechanism to Therapy: Targeting the Axis

Elucidating a novel mechanism is a significant achievement, but the study went further by demonstrating its therapeutic tractability. The team validated the axis as a druggable target through two distinct and compelling strategies in mouse models of PCa:

• Drug Repurposing: They identified that Tenapanor, an existing FDA-approved drug, could effectively disrupt the interaction between YY1, NUSAP1, and HIF-1α. Targeted delivery of Tenapanor to TAMs not only inhibited tumor growth but also significantly increased the infiltration of tumor-fighting CD8+ T cells, effectively warming up the "cold" TME.
• A Novel DNA-PROTAC: Recognizing that transcription factors like YY1 are traditionally "undruggable," the researchers engineered an innovative therapeutic tool: a tetrahedral DNA nanostructure termed YY1-DcTAC. This "smart" nanodevice functions like a targeted PROTAC (PROteolysis TArgeting Chimera). It contains a sensor that recognizes CD206 mRNA, a marker of M2-like TAMs. Upon binding, the nanostructure opens and releases a payload that directs YY1 for degradation. This highly specific approach also demonstrated potent anti-tumor effects and enhanced T-cell infiltration.

Finally, using a myeloid-specific YY1 conditional knockout mouse model, the researchers provided definitive genetic proof that YY1 in TAMs is essential for driving PCa's immune evasion.

Broader Implications and the Path Forward

The findings from Li et al. carry implications that extend far beyond prostate cancer. The discovery of a phase separation-driven regulatory cascade provides a new paradigm for understanding how cells translate environmental cues into stable phenotypic states, particularly in the context of immuno-oncology. It offers a compelling explanation for the resilience of the immunosuppressive TME.

Moreover, the study provides a powerful blueprint for targeting previously intractable intracellular proteins. The elegant design of the YY1-DcTAC highlights a new frontier in therapeutic development, where programmable logic is built directly into the drug molecule. Accelerating this requires scalable platforms for AI-aided DNA design and high-throughput construct validation to rapidly iterate and optimize these complex biological programs.

While challenges remain for the clinical translation of DNA nanostructures—including stability, immunogenicity, and large-scale manufacturing—this work opens an exciting new chapter. By cracking the code of a key immunosuppressive axis, it provides both a deeper understanding of cancer biology and a tangible set of strategies to finally turn the tide against "cold" tumors.

References

1. Li, W., Chen, S., Lu, J., et al. (2025). YY1 enhances HIF-1α stability in tumor-associated macrophages to suppress anti-tumor immunity of prostate cancer in mice. Nature Communications.
2. Chen, S., et al. (2023). YY1 complex in M2 macrophage promotes prostate cancer progression by upregulating IL-6. Journal for ImmunoTherapy of Cancer.
3. Hsu, K. F., et al. (2019). The role of YY1 in the regulation of the expression of PD-L1 in non-small cell lung cancer. Journal for ImmunoTherapy of Cancer.
4. Wang, Z., et al. (2023). The role of YY1 in tumor immunity: a friend or a foe? Frontiers in Oncology.