LSD1 demethylase and the methyl-binding protein PHF20L1 prevent SET7 methyltransferase–dependent proteolysis of the stem-cell protein SOX2

Chunxiao Zhang,Nam Hoang,Feng Leng,Lovely Saxena,Logan Lee,Salvador Alejo,Dandan Qi,Anthony Khal,Hong Sun,Fei Lu,Hui Zhang

doi:10.1074/jbc.ra117.000342

Chunxiao Zhang, Nam Hoang + Show 9 more

Open Access

https://doi.org/10.1074/jbc.ra117.000342

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Abstract

The pluripotency-controlling stem-cell protein SRY-box 2 (SOX2) plays a pivotal role in maintaining the self-renewal and pluripotency of embryonic stem cells and also of teratocarcinoma or embryonic carcinoma cells. SOX2 is monomethylated at lysine 119 (Lys-119) in mouse embryonic stem cells by the SET7 methyltransferase, and this methylation triggers ubiquitin-dependent SOX2 proteolysis. However, the molecular regulators and mechanisms controlling SET7-induced SOX2 proteolysis are unknown. Here, we report that in human ovarian teratocarcinoma PA-1 cells, methylation-dependent SOX2 proteolysis is dynamically regulated by the LSD1 lysine demethylase and a methyl-binding protein, PHD finger protein 20-like 1 (PHF20L1). We found that LSD1 not only removes the methyl group from monomethylated Lys-117 (equivalent to Lys-119 in mouse SOX2), but it also demethylates monomethylated Lys-42 in SOX2, a reaction that SET7 also regulated and that also triggered SOX2 proteolysis. Our studies further revealed that PHF20L1 binds both monomethylated Lys-42 and Lys-117 in SOX2 and thereby prevents SOX2 proteolysis. Down-regulation of either LSD1 or PHF20L1 promoted SOX2 proteolysis, which was prevented by SET7 inactivation in both PA-1 and mouse embryonic stem cells. Our studies also disclosed that LSD1 and PHF20L1 normally regulate the growth of pluripotent mouse embryonic stem cells and PA-1 cells by preventing methylation-dependent SOX2 proteolysis. In conclusion, our findings reveal an important mechanism by which the stability of the pluripotency-controlling stem-cell protein SOX2 is dynamically regulated by the activities of SET7, LSD1, and PHF20L1 in pluripotent stem cells.

Highlights

The pluripotency-controlling stem-cell protein SRY-box 2 (SOX2) plays a pivotal role in maintaining the self-renewal and pluripotency of embryonic stem cells and of teratocarcinoma or embryonic carcinoma cells
We found that a novel methylated lysine residue, Lys-42, in SOX2 is recognized by LSD1 for demethylation, and this lysine is regulated by SET7 (Fig. 2)
Our studies revealed that PHF20L1 recognizes both the monomethylated Lys-42 and Lys-117 residues in SOX2, and its binding to these methylated lysine residues prevents the degradation of SOX2 protein

Summary

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The lysine-specific demethylase 1 (LSD1,2 called KDM1A) was originally identified as a histone demethylase that removes the methyl group from the mono- and dimethylated lysine 4 in histone H3 (H3K4) [1], which is associated with active chromatin structure for gene activation [2]. Regulation of methylated SOX2 by LSD1 and PHF20L1 monomethylated on lysine 119 (equivalent to Lys-117 in human SOX2) by SET7 in mouse embryonic stem cells, and this methylation triggers the ubiquitin-dependent proteolysis of modified SOX2 protein [34]. We have previously developed a novel class of LSD1 inhibitors, and our studies showed that these inhibitors potently inhibited the self-renewal of pluripotent mouse embryonic stem cells and teratocarcinoma and embryonic carcinoma cells through transcriptional down-regulation of SOX2 and other pluripotent stem cell proteins, such as OCT4 [6, 35]. Our studies further indicate that the protein stability of methylated SOX2 is regulated by PHF20L1, a protein that contains a methyl-binding domain [37, 38] These LSD1- and PHF20L1-dependent regulatory mechanisms are conserved in mouse embryonic stem cells. Our studies indicate that the methylation-dependent proteolysis of SOX2 is highly regulated in embryonic stem cells and pluripotent cancer cells

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Discussion

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