Recently, the research team led by Professor Jun Pang from the Department of Urology at The Seventh Affiliated Hospital of Sun Yat-sen University discovered that cyclin-dependent kinase 12 (CDK12) can directly phosphorylate the pioneer transcription factor FOXA1, thereby activating a critical new pathway that drives prostate cancer progression. This study is the first to identify a novel phosphorylation site (S234) on the FOXA1 protein and elucidates the complete mechanism by which phosphorylation at this site upregulates the expression of the oncogene MDM2, leading to the degradation of the tumor suppressor protein p53, ultimately promoting tumor cell survival and proliferation. Targeted inhibition of CDK12 can effectively block this pathway, restore p53 function, and induce cancer cell apoptosis, providing a highly promising new strategy for the treatment of advanced prostate cancer. The related findings have been published in Research under the title "CDK12-Mediated Phosphorylation of FOXA1 Promotes Prostate Cancer Progression via the MDM2–p53 Axis."

Research Background
Prostate cancer is one of the most common malignant tumors in men, ranking second in global male cancer incidence and first in Europe and North America. Although therapies targeting androgen and the androgen receptor have made significant advances, approximately 30% of patients still progress to advanced stages such as metastatic castration-resistant prostate cancer and neuroendocrine prostate cancer, posing enormous challenges for clinical treatment. In recent years, the research focus has gradually shifted towards core regulators of the androgen receptor to seek new pathways for overcoming drug resistance.
Among these, the pioneer transcription factor FOXA1 is the third most frequently mutated gene in prostate cancer and is crucial for the initiation and development of the disease. Its function is precisely regulated by post-translational modifications, yet the specific mechanisms are not fully understood. Concurrently, the kinase CDK12 also plays a significant role in prostate cancer, and its genetic mutations are closely associated with tumor progression and poor prognosis. This study is the first to link these two key molecules, revealing a novel CDK12-driven signaling pathway that promotes tumor development through FOXA1 modification.
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Research Progress
This study systematically and progressively elucidated the novel mechanism by which the CDK12-FOXA1-MDM2-p53 pathway drives prostate cancer progression. Initial drug and reporter gene screening revealed that the CDK12/13 small molecule inhibitor THZ531 significantly inhibits the transcriptional activity of FOXA1. Further experiments confirmed that CDK12 can directly bind to and phosphorylate the FOXA1 protein both in vitro and in vivo (Fig. 1).
Subsequently, through bioinformatics analysis and experimental validation, the team mapped the CDK12-mediated phosphorylation of FOXA1 to serine 234 (S234). This site is highly conserved and located within the DNA-binding domain of FOXA1. The research not only constructed site-specific mutants (S234A and S234E) but also successfully generated a specific antibody recognizing pS234-FOXA1, providing a crucial tool for mechanistic studies (Fig. 2). Further exploration of downstream genes regulated by activated FOXA1 revealed that FOXA1 can directly bind to and upregulate the transcription of the MDM2 gene. MDM2 is a well-known E3 ubiquitin ligase whose core function is to promote the ubiquitination and degradation of the tumor suppressor protein p53. Therefore, CDK12, by phosphorylating FOXA1, activates the "FOXA1-MDM2-p53" signaling axis, leading to decreased stability of the p53 protein, thereby inhibiting cell apoptosis and promoting cancer cell survival and proliferation (Fig. 3). Finally, it was clarified that the phosphorylation modification does not alter the cellular localization of FOXA1 but significantly enhances its chromatin DNA-binding affinity and transcriptional activity. Functional experiments demonstrated that S234 phosphorylation potently promotes the growth capacity of prostate cancer cells both in vitro and in vivo. More importantly, treatment of a nude mouse xenograft tumor models with the CDK12 inhibitor THZ531 effectively blocked this pathway, reduced MDM2 levels, stabilized the p53 protein, and consequently significantly inhibited tumor growth (Fig. 4).

Future Prospects
The findings of this study provide an important perspective for understanding the progression mechanisms of prostate cancer and developing novel therapies. The team is the first to report the direct phosphorylation of FOXA1 by CDK12 and to identify S234 as a novel functional site, adding a key piece to the understanding of the post-translational regulatory network of FOXA1. Simultaneously, the study is the first to directly link FOXA1 to the classical MDM2-p53 axis that regulates p53 protein stability, revealing a novel mechanism by which FOXA1 promotes tumor growth.
This research establishes "CDK12-FOXA1-MDM2-p53" as a complete pro-oncogenic signaling axis. This suggests that for prostate cancer patients with aberrant CDK12 activation or high FOXA1 expression, CDK12 inhibitors (such as THZ531) may be an effective treatment strategy. By targeting the upstream component of this pathway, it is possible to simultaneously affect FOXA1 activity and p53 stability, achieving an anticancer effect of "killing two birds with one stone."
Although this study focuses on the core role of this pathway in apoptosis and proliferation, the impact of FOXA1-S234 phosphorylation on genome-wide chromatin plasticity, gene expression profiles, and androgen receptor signaling remains to be further explored. Furthermore, promoting the clinical translation of CDK12 inhibitors and exploring their combination with existing therapies will be important directions for future research.

The complete study is accessible via DOI:10.34133/research.0990