Study reveals role of DCAF1 protein in colon cancer development through phosphorylation of EZH2

Initially, DDB1 and CUL4-associated factor 1 (DCAF1) was identified as a protein that interacts with human immunodeficiency virus 1 (HIV-1) virion-associated protein (Vpr) and regulates cell cycles and proliferation cellular. Although most research related to DCAF1, also known as HIV-1 Vpr binding protein (VprBP), has reported on its function as an adapter in the Cullin 4 A E3 ubiquitin ligase complex, recent studies reported intrinsic kinase activity in DCAF1 and identified H2AT120 as the first phosphorylation target of DCAF1.

Study: Phosphorylation and stabilization of EZH2 by DCAF1/VprBP triggers aberrant gene silencing in colon cancer. Image Credit: Lukasz Pawl Sczepanski / Shutterstock.com

Background

Gene expression profiling has shown the gene-selective corepressor function of DCAF1, which is associated with the targeting and silencing of growth regulator genes in cancer cells. The growth regulator gene is inactivated by DCAF1, which depends on the phosphorylation of H2AT120 (H2AT120p). This inactivation is based on a point mutation of T120 in H2A that disables DCAF1 to repress transcription in chromatin.

The potential for DCAF1 transrepression in cancer cells can be eliminated by kinase-dead mutations. Thus, an H2AT120p-dependent mechanism is associated with DCAF1 function in maintaining inactive chromatin states and triggering oncogenic transformation.

Greater expression of DCAF1 and elevated levels of H2AT120p have been observed in several types of cancer, especially colon cancer. Several studies have indicated the importance of DCAF1 kinase activity in tumorigenesis and the importance of DCAF1-mediated H2AT120p in the inactivation of growth regulator genes. A small molecule inhibitor known as B32B3 has been shown to inhibit DCAF1 kinase activity and tumor growth in organoid and xenograft models.

It is imperative to understand whether phosphorylation of non-histone proteins is required for oncogenic events promoted by DCAF1. This will help to elucidate the existence of any post-translational mechanism associated with the activation of oncogenic cell signaling.

Enhancer of Zeste Homolog 2 (EZH2) is a highly conserved histone lysine methyltransferase that triggers trimethylation of the nucleosomal histone H3 at lysine 27 (H3K27me3). EZH2 has been found overexpressed or mutated in many types of cancer and appears to be involved in tumor initiation and progression with poor clinical prognosis. Several studies have reported that the enzymatic activity of EZH2 is regulated by numerous post-translational modifications, including phosphorylation.

In breast cancer, EZH2 enzymatic activity towards H3K27 is attenuated by AMPK-mediated phosphorylation at T311, which then triggers cytoplasmic localization and metastasis of EZH2. Additionally, EZH2 phosphorylation has been associated with repression of tumor suppressor genes.

The exact mechanism responsible for modulating EZH2 phosphorylation that influences the progression of tumorigenesis remains unclear.

About the study

A recent Nature Communication reveals that DCAF1 is overexpressed and phosphorylates EZH2 in colon cancer cells.

Mass spectrometry analysis allowed the identification of T367 of EZH2 as a key phosphorylation site for DCAF1. This finding was validated using a newly developed EZH2T367 (EZH2T367p) phosphorylation-specific antibody.

In colon cancer, DCAF1 has been shown to be overexpressed, which catalyzes H2AT120p to inactivate genes associated with the regulation of cell growth and proliferation. The possibility of additional DCAF1 functions mediated by non-histone substrates was explored in this study.

Identifying the association between DCAF1 and non-histone modifications could provide better insights into oncogenic signaling pathways. This knowledge would help develop more effective strategies to treat colon and other types of cancer.

Study results

In the present study, researchers elucidate the underlying mechanism by which DCAF1 influences EZH2T367p during colon cancer development was demonstrated in this study.
To this end, DCAF1-mediated EZH2T367p has been shown to stimulate cancer cell growth through accumulation of EZH2 protein and activation of EZH2 enzyme activity that catalyzes H3K27me3. Subsequent inactivation of growth regulator genes by H3K27me3 causes uncontrolled cell proliferation and growth.

DCAF1-mediated EZH2T367p modulates the strength and nature of how EZH2 interacts with other components of the repressive polycomb 2 complex (PRC2). Ultimately, EZH2 enhances the stability and activity of histone methyltransferase (HMT) towards H3K27. Notably, T367p has been shown to be an extremely important factor for EZH2 stability, which allows efficient regulation of EZH2 protein levels.

Upregulation of DCAF1 was observed in colon cancer patient samples and correlated with EZH2T367p levels. Moreover, low p38 expression was distributed throughout the nucleus and cytoplasm in colon cancer cell lines. In the future, biological and functional analyzes of DCAF1 and p38 are needed to better understand their specific roles in colon cancer.

The current study not only identified EZH2T367p as a biomarker to predict colon cancer, but also provided a novel approach to treat this disease. Targeting DCAF1 kinase activity against EZH2, for example, could effectively prevent the development of colon cancer.

The DCAF1 inhibitor B32B3 was able to inhibit uncontrolled cell growth linked to colon cancer. Besides, alive, experiments revealed that a combination of Taz and B32B3 had minimal side effects on healthy colon cells and effectively inhibited colon tumorigenesis.

conclusion

DCAF1-mediated EZH2T367p appears to be oncogenic, as DCAF1 inhibition/knockdown reactivates a large number of tumor suppressor genes that prevent cancer cell proliferation. Organoid and xenograft models revealed that efficient targeting of DCAF1 and EZH2 through a pharmacological agent could alter their ability to trigger oncogene gene silencing and limit colon tumor growth.