Control of Adipogenesis by the SUMO-Specific Protease SENP2

Abstract

Here, we demonstrate that SENP2, a desumoylating enzyme, plays a critical role in the control of adipogenesis. SENP2 expression was markedly increased upon the induction of adipocyte differentiation, and this increase was dependent on protein kinase A activation. Remarkably, knockdown of SENP2 led to a dramatic attenuation of adipogenesis with a marked decrease in PPAR␥ and C/EBP␣ mRNA levels. Knockdown of SENP2 also caused a marked reduction in the level of C/EBP␤ protein but not in that of C/EBP␤ mRNA. Interestingly, sumoylation of C/EBP␤ dramatically increased its ubiquitination and destabilization, and this increase could be reversed by SENP2. In addition, overexpression of C/EBP␤ could overcome the inhibitory effect of SENP2 knockdown on adipogenesis. Furthermore, SENP2 was absolutely required for adipogenesis of preadipocytes implanted into mice. These results establish a critical role for SENP2 in the regulation of adipogenesis by desumoylation and stabilization of C/EBP␤ and in turn by promoting the expression of its downstream effectors, such as PPAR␥ and C/EBP␣.A large number of transcription factors are modified by the small ubiquitin (Ub)-related modifier (SUMO), and this covalent modification regulates their transcriptional activities (12,16,17). Unlike ubiquitination, SUMO modification is not a signal for protein degradation. SUMO modification regulates the target proteins through various mechanisms such as affecting cellular localization, protein-protein interaction, or stability of the target proteins. SUMO modification (sumoylation) is a reversible process that is catalyzed by SUMO-specific proteases (SENPs) (27). Six SENPs (SENP1, -2, -3, -5, -6, and -7) have been identified in humans, and they have different cellular localization and substrate specificities (42). Although the biochemical properties of SENPs have been well documented, their specific targets and physiological roles are known in a limited number of cases. SENP1 plays a key role in the hypoxic response by regulating HIF1␣ stability (6). SUSP4, a newly identified mouse SENP, inhibits cell growth by positively regulating p53 by promoting the self-ubiquitination of Mdm2 (21). In addition, overexpression of SENP2 is involved in the downregulation of ␤-catenin, whereas the direct target of SENP2 in this process is unknown (19). It has also been reported that SENP5 regulates cell division and mitochondrial morphology; however, the targets of SENP5 have not been identified (9, 46).The adipose tissues function as a reservoir of excessive energy. They also secrete adipokines that regulate physiological and pathological events involving energy metabolism, insulin sensitivity, atherogenesis, and inflammatory responses. Adipocyte differentiation from preadipocytes occurs by serial inductions of transcription factors, and this process is tightly regulated. Expression of C/EBP␤ and C/EBP␦ is induced immediately after stimulation, followed by the induction of PPAR␥ and C/EBP␣ (5, 43). PPAR␥ induces several adipocyte-specific genes, including aP2...

Role of UBC9 in the Regulation of the Adipogenic Program in 3T3-L1 Adipocytes

“…The effect of UBC9 knockdown on the expression levels of adipogenic transcription factors is of interest, in view of the reported ability of UBC9 to modulate PPAR␥ transcriptional activity through SUMOylation of specific amino acid residues in this transcription factor (31)(32)(33). Other adipogenic transcription factors, such as C/EBP␣ and C/EBP␤, are also SUMOylated (34,35), and it has recently been suggested that interfering with the de-SUMOylation step via knockdown of a specific SUMO protease, such as SENP2 (SUMO1/sentrin/SMT3 specific peptidase-2), affects C/EBP␤ stability and the extent of adipogenesis (36). However, in this study, overexpression of the catalytically inactive mutant of UBC9, in which the cysteine residue (Cys93) required for the SUMO-conjugating activity of the enzyme was replaced by alanine, resulted in indistinguishable effects on C/EBP␦, C/EBP␣, and PPAR␥ mRNA expression as well as on overall adipogenesis, compared with both UBC9-overexpressing and mock-infected cells (Fig.…”

Transcriptional Regulation of Adipocyte Differentiation: A Central Role for CCAAT/Enhancer-binding Protein (C/EBP) β

“…Consequently, PIAS1 is a negative regulator in adipogenesis by promoting the SUMOlation and degradation of C/EBP␤. Conversely, the SUMO-specific protease Sentrin/SUMO-specific protease 2 (SENP2) plays a critical role in promoting adipogenesis by de-SUMOlation and stabilization of C/EBP␤ (70).…”

Small Ubiquitin-like Modifier (SUMO) Protein-specific Protease 1 De-SUMOylates Sharp-1 Protein and Controls Adipocyte Differentiation

“…SENP1 de-SUMOylates Sharp-1, not C/EBP␤, a target of SENP2 in adipogenesis. Interestingly, Chung et al (24) didn't detect any change of SENP1 expression in 3T3-L1 induced by DMI. However, in our study, we clearly demonstrated the increase of SENP1 in MEF cells when induced by DMIR.…”

“…Liu et al (23) found that PIAS1 promotes C/EBP␤ SUMOylation and inhibits adipogenesis. Chung et al (24) found that a de-SUMOylation protease, SENP2, can directly modulate C/EBP␤ SUMOylation and its stability and, consequently, is essential for adipogenesis. Here we provide more evidence for SUMOylation in the regulation of adipogenesis by showing that SENP1, another member of SENP family, is also essential for adipogenesis.…”