Great progress has been achieved in the study of the role of TGF-β signaling in triggering epithelial-mesenchymal transition (EMT) in a variety of cancers; however, the regulation of TGF-β signaling during EMT in mammary tumor metastasis has not been completely defined. In the present study, we demonstrated that OVOL2, a zinc finger transcription factor, inhibits TGF-β signaling-induced EMT in mouse and human mammary tumor cells, as well as in mouse tumor models. Data from the Oncomine databases indicated a strong negative relationship between OVOL2 expression and breast cancer progression. Moreover, our experiments revealed that OVOL2 inhibits TGF-β signaling at multiple levels, including inhibiting Smad4 mRNA expression and inducing Smad7 mRNA expression, blocking the binding between Smad4 and target DNA, and interfering with complex formation between Smad4 and Smad2/3. These findings reveal a novel mechanism that controls the TGF-β signaling output level in vitro and in vivo. The modulation of these molecular processes may represent a strategy for inhibiting breast cancer invasion by restoring OVOL2 expression.

Wnt/β-catenin signaling plays a key role in regulating adipogenesis through indirectly inhibiting the expression of C/EBPα and peroxisome proliferator–activated receptor γ (PPARγ); however, the detailed molecular mechanism remains poorly understood. Moreover, the factor(s) that determines the Wnt/β-catenin output level during adipogenesis is also not completely defined. In this study, we showed that Pygo2 exhibited a declined expression pattern during adipocyte differentiation, resulting in an attenuated Wnt/β-catenin output level. The mechanism study indicated that Pygo2 inhibition led to the downregulation of Axin2, a constitutive Wnt target, in the cytoplasm. Consequently, Axin2-bound GSK3β was released and translocated into the nucleus to phosphorylate C/EBPβ and Snail, resulting in an increase in the DNA binding activity of C/EBPβ and decreased protein stability of Snail, which subsequently activated the expression of C/EBPα and PPARγ. Consistent with this, embryonic fibroblasts from Pygo2−/− mice exhibited spontaneous adipocyte differentiation, and adipocyte precursor–specific Pygo2-deficient mice exhibited increased adiposity with decreased energy expenditure. We further showed impaired glucose tolerance and decreased systemic insulin sensitivity in Pygo2-deficient mice. Our study revealed an association between Pygo2 function and obesity or diabetes.

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Poly(ADP‐ribosyl)ation (PARylation) is a post‐translational modification by which poly ADP‐ribose (PAR) polymers are covalently added to proteins through a PAR polymerase (PARP). Here, we identify that the transcriptional regulator, OVOL2, is a novel substrate for PARP1 and can be PARylated at residues Lysine 145, Lysine 176, and Lysine 212, within the C2H2 zinc‐fingers domain. PARylated OVOL2 acts as a transcriptional suppressor directly inhibiting downstream expression of the E3 ligase, Skp2, which promotes ubiquitin‐dependent degradation of Cyclin E, thus leading to an accumulation of Cyclin E during cell cycle progression. As a result, overexpression of OVOL2, but not the non‐PARylated OVOL2‐3K/A mutant, induces aberrant centrosome amplification and chromosome instability, resulting in aneuploidy and subsequent cell death. Overexpression of PARylated OVOL2 in vivo resulted in a significant reduction in tumor progression, supporting the function of OVOL2 as a tumor suppressor, which is highly regulated by PARylation. Support or Funding Information This work was supported in part by Grants R‐154‐000‐637‐511 from the Ministry of Education (MOE), National Medical Research Council (NMRC), Singapore to Y.C.L. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.