Lysine methylation of non-histone proteins has emerged as a key regulator of many cellular functions. Although less studied than other post-translational modifications such as phosphorylation and acetylation, the number of known methylated nonhistone proteins is rapidly expanding. We have identified the p21-activated kinase 4 (PAK4) as a new substrate for methylation by the protein lysine methyltransferase SETD6. Our data demonstrate that SETD6 methylates PAK4 both in vitro and at chromatin in cells. Interestingly, depletion of SETD6 in various cellular systems significantly hinders the activation of the Wnt/ ␤-catenin target genes. PAK4 was recently shown to regulate ␤-catenin signaling, and we show that SETD6 is a key mediator of this pathway. In the presence of SETD6, the physical interaction between PAK4 and ␤-catenin is dramatically increased, leading to a significant increase in the transcription of ␤-catenin target genes. Taken together, our results uncover a new regulatory layer of the Wnt/␤-catenin signaling cascade and provide new insight into SETD6 biology.

Lysine methylation, catalyzed by protein lysine methyltransferases (PKMTs), is a key player in regulating intracellular signaling pathways. However, the role of PKMTs and the methylation of nonhistone proteins during the cell cycle are largely unexplored. In a recent proteomic screen, we identified that the PKMT SETD6 methylates PLK1—a key regulator of mitosis and highly expressed in tumor cells. In this study, we provide evidence that SETD6 is involved in cell cycle regulation. SETD6-deficient cells were observed to progress faster through the different mitotic steps toward the cytokinesis stage. Mechanistically, we found that during mitosis SETD6 binds and methylates PLK1 on two lysine residues: K209 and K413. Lack of methylation of these two residues results in increased kinase activity of PLK1, leading to accelerated mitosis and faster cellular proliferation, similarly to SETD6-deficient cells. Taken together, our findings reveal a role for SETD6 in regulating mitotic progression, suggesting a pathway through which SETD6 methylation activity contributes to normal mitotic pace.

There is growing interest in understanding how dysregulated autophagy may contribute to pathogenesis of disease. Most frequently, disease states are associated with diminished autophagy, mostly attributed to genetic variation in autophagy genes and/or to dysfunctional posttranscriptional mechanisms. In human adipose tissue (AT), in obesity, expression of autophagy genes is upregulated and autophagy is likely activated, associating with adipose dysfunction. This review explores the emerging role of transcriptional mechanisms regulating AT autophagy in obesity.

The transcriptional coactivator BRD4 has a fundamental role in transcription regulation and thus became a promising epigenetic therapeutic candidate to target diverse pathologies. However, the regulation of BRD4 by posttranslational modifications has been largely unexplored. Here, we show that BRD4 is methylated on chromatin at lysine-99 by the protein lysine methyltransferase SETD6. BRD4 methylation negatively regulates the expression of genes that are involved in translation and inhibits total mRNA translation in cells. Mechanistically, we provide evidence that supports a model where BRD4 methylation by SETD6 does not have a direct role in the association with acetylated histone H4 at chromatin. However, this methylation specifically determines the recruitment of the transcription factor E2F1 to selected target genes that are involved in mRNA translation. Together, our findings reveal a previously unknown molecular mechanism for BRD4 methylation–dependent gene-specific targeting, which may serve as a new direction for the development of therapeutic applications.

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