STAT6 protein: A key transcription factor in acetylation-mediated macrophage M2 polarization and antitumor immunity

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This article focuses on the molecular characteristics and immune regulatory functions of signal transducer and activator of transcription 6 (STAT6), systematically elaborating its role as a STAT family member in IL-4 signaling pathway activation and immune system regulation, analyzing the pathological significance of STAT6 in mediating tumor growth and metastasis by driving macrophage M2 polarization, and exploring the molecular mechanism by which TRIM24 enhances STAT6 recruitment and promotes K383 acetylation through mediating K63-linked ubiquitination of CBP at the K119 site, thereby inhibiting STAT6 transcriptional activity and M2 polarization.

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STAT6 Protein: A Key Transcription Factor in Acetylation-Modulated Macrophage M2 Polarization and Antitumor Immunity

Summary: This article focuses on the molecular characteristics and immunoregulatory functions of signal transducer and activator of transcription 6 (STAT6), systematically elaborating its role as a STAT family member in IL-4 signaling pathway activation and immune system regulation, analyzing the pathological significance of STAT6 in driving macrophage M2 polarization to mediate tumor growth and metastasis, and discussing the molecular mechanism by which TRIM24 enhances STAT6 recruitment and promotes K383 acetylation through mediating K63-linked ubiquitination of CBP at K119, thereby inhibiting STAT6 transcriptional activity and M2 polarization.

I. The STAT Family and the Molecular Positioning of STAT6.

The signal transducer and activator of transcription family has six members, of which STAT6 is one. Previous studies have shown that STAT6 not only participates in the activation of the IL-4 signaling pathway and the regulation of the immune system, but also mediates tumor growth and metastasis by driving macrophage M2 polarization; however, the specific mechanism remains unclear. This knowledge gap constitutes the core scientific question of this study: whether the process by which STAT6 drives M2 polarization involves fine regulation at the post-translational modification level, and which molecular events can determine the transcriptional activity state of STAT6. From the perspective of the functional division of the STAT family, STAT6 is the core transcription factor of the IL-4/IL-13 signaling axis, and its activation directly determines the initiation of downstream type 2 immune gene programs; therefore, the molecular details of its activity regulation have broad significance beyond a single pathway.

II. The Therapeutic Target Value of Tumor-Associated Macrophages and M2 Polarization.

TAMs are mature M2-polarized macrophages derived from blood monocytes recruited by molecules produced by cancer cells and stromal cells at the tumor site. In the tumor microenvironment, M2 macrophages support tumor progression by secreting immunosuppressive cytokines, promoting angiogenesis, and remodeling tissue, and their infiltration density is often associated with poor patient prognosis. Approaches that target TAMs to inhibit tumor growth and metastasis by suppressing the activation of M2 macrophages or inducing M1-type pro-inflammatory responses in TAMs have been used in the clinical treatment of various solid tumors. The core logic of this therapeutic strategy lies in reshaping the polarization direction of macrophages in the tumor microenvironment, converting the tumor-promoting M2 phenotype into an antitumor M1 phenotype; as a key driving transcription factor of M2 polarization, STAT6 naturally becomes the core intervention node in this strategy.

III. Discovery of the Interaction Between TRIM24 and CBP.

On September 25, 2019, the international academic journal Nature Communications published online the latest collaborative research results of the relevant research team, “Modulation of M2 macrophage polarization by the crosstalk between Stat6 and Trim24”. Through high-throughput transcriptome sequencing combined with protein mass spectrometry analysis, this study found that TRIM24, an E3 ubiquitin ligase of the TRIM family proteins, can bind to the acetyltransferase CBP and mediate K63-linked ubiquitination of CBP at the K119 site. This discovery links E3 ubiquitin ligase, acetyltransferase, and transcription factor together on the same regulatory axis, revealing a new function of non-degradative ubiquitination in the regulation of immune cell polarization——K63-linked ubiquitin chains do not direct protein degradation but instead serve as a signaling platform to enhance protein-protein interactions, and this mechanistic feature is a key innovation of the study.

IV. The Molecular Pathway of STAT6 K383 Acetylation and Inhibition of Transcriptional Activity.

TRIM24-mediated K63-linked ubiquitination of CBP at K119 enhances the recruitment of CBP to STAT6 and promotes CBP-mediated acetylation of STAT6 at the K383 site, thereby inhibiting STAT6 transcriptional activity and M2-type polarization of macrophages. This pathway can be summarized as a four-step cascade: “TRIM24—CBP K119 ubiquitination—STAT6 K383 acetylation—inhibition of transcriptional activity”. Its molecular logic is that acetylation of STAT6 does not enhance its function but acts as a negative regulatory mark that weakens its transcriptional activation capacity; CBP plays a dual role in this process, being both the acetylase of STAT6 and having its own activity regulated by TRIM24-mediated ubiquitination. This “modification of a modification” constitutes a precise hierarchical regulatory network that enables the activity state of STAT6 to be precisely set by upstream signals.

V. Consequences of TRIM24 Deficiency for M2 Polarization and Antitumor Immunity.

When TRIM24 is deficient, Lys383 acetylation in STAT6 is suppressed, and M2-type polarization of macrophages is promoted, potentially disrupting antitumor immune responses. This phenotype conversely validates the functional necessity of the TRIM24-STAT6 acetylation axis: the presence of TRIM24 is equivalent to setting a “brake” on the transcriptional activity of STAT6 to prevent excessive M2 polarization; when this brake fails, M2 polarization is enhanced, the tumor microenvironment tilts toward immunosuppression, and antitumor immune responses are consequently impaired. This discovery not only elucidates the specific molecular mechanism by which STAT6 regulates M2 polarization but also provides a potential intervention approach for targeting this axis to enhance antitumor immunity——namely, limiting M2 polarization by enhancing STAT6 K383 acetylation or mimicking the function of TRIM24.

VI. Conclusion.

In basic research on STAT6 and the development of tumor immunotherapy, high-quality recombinant STAT6 protein is a core tool for dissecting its acetylation modification regulation, evaluating the TRIM24-CBP-STAT6 axis interactions, and conducting inhibitor screening. The GST tag facilitates efficient purification through glutathione affinity chromatography and can serve as a detection tag for analyses such as enzyme-linked immunosorbent assay and surface plasmon resonance. To meet the needs of STAT6 functional research and exploration of the mechanisms regulating macrophage polarization, UA provides STAT6 GST Tag Protein, Human. This product is suitable for applications including research on the interaction mechanisms of STAT6 with CBP and TRIM24, in vitro analysis of STAT6 K383 acetylation modification, small-molecule screening and evaluation targeting STAT6 acetylation regulation, and the development of tumor immunotherapy strategies related to M2 macrophage polarization.

This article is reviewed and published by the technical expert team of UA

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