Plakoglobin regulates adipocyte differentiation independently of the Wnt/β-catenin signalling pathway

Abstract

The scaffold protein 14-3-3ζ is an established regulator of adipogenesis and postnatal adiposity. We and others have demonstrated that the 14-3-3ζ interactome to be diverse and dynamic, and it can be examined to identify novel regulators of physiological processes, including adipogenesis. In the present study, we sought to determine if factors that influence adipogenesis could be identified in the 14-3-3ζ interactome found in white adipose tissue of lean or obese TAP-tagged-14-3-3ζ overexpressing mice. Using mass spectrometry, changes in the abundance of novel, as well as established, adipogenic factors within the 14-3-3ζ interactome could detected. One novel candidate is plakoglobin, the homolog of the known adipogenic inhibitor β-catenin, and herein, we report that plakoglobin is involved in adipocyte differentiation. Plakoglobin is expressed in murine 3T3-L1 cells and is primarily localized to the nucleus, where its abundance decreases during adipogenesis. Ectopic overexpression and siRNA-mediated depletion of plakoglobin had dual effects on inhibiting adipogenesis and reducing PPARγ2 expression. Plakoglobin depletion in human adipose-derived stem cells also impaired adipogenesis and reduced lipid accumulation post-differentiation. Transcriptional assays indicated that plakoglobin does not participate in Wnt/β-catenin signaling, as its depletion did not affect Wnt3a-mediated SUPERTOPFlash activity. Taken together, our results establish plakoglobin as a novel regulator of adipogenesis in vitro and highlights the ability of using the 14-3-3ζ interactome to discover undiscovered pro-obesogenic factors.

14-3-3ζ regulates adipogenesis by modulating chromatin accessibility during the early stages of adipocyte differentiation

“…Through the use of CRISPR-Cas9 genome editing, we developed a useful model to explore the nuclear 14-3-3ζ interactome of APCs during adipogenesis, and this led to the discovery that 14-3-3ζ primarily acts during the early stages of adipocyte differentiation to aid in the reorganization of chromatin to allow for adipogenic gene, promoter and enhancer regions to be accessible. These findings, combined with our prior research, broaden our understanding of the importance of 14-3-3ζ in adipocyte development, metabolism, and glucose and lipid homeostasis (9, 11, 15–17). Furthermore, our study clearly demonstrates for the first time that 14- 3-3ζ, a ubiquitously expressed molecular scaffold protein, has critical upstream regulatory roles in adipogenesis.…”

“…In fact, we previously showed that 14-3-3ζ interacts with C/EBP-β during adipogenesis(9). As we have previously reported that mass spectrometry can be used to elucidate the 14-3-3ζ interactome under physiological and pathophysiological contexts (14, 15), we sought to define the nuclear 14-3-3ζ interactome during the differentiation of preadipocytes, with the goal of identifying novel adipogenic transcription factors or co-regulators that could be anchored by 14-3-3ζ.…”

“…We further sought to determine the mechanisms by which 14-3-3ζ influences APCs differentiation through deciphering its interactome during the early stages of adipogenesis. Our previous studies have already demonstrated the promising value of mining the 14-3-3ζ interactome to identify novel regulators of adipogenesis (14, 15). For example, we recently identified plakoglobin, the homolog of the adipogenic inhibitor β-catenin, among proteins enriched in the 14-3-3ζ interactome in visceral adipose tissue of mice subjected to HFD (15).…”

“…Our previous studies have already demonstrated the promising value of mining the 14-3-3ζ interactome to identify novel regulators of adipogenesis (14, 15). For example, we recently identified plakoglobin, the homolog of the adipogenic inhibitor β-catenin, among proteins enriched in the 14-3-3ζ interactome in visceral adipose tissue of mice subjected to HFD (15). To increase the likelihood of detecting novel adipogenic transcriptional regulators, we developed a novel cell model to elucidate the nuclear 14-3-3ζ interactome ( Fig.…”

“…We first used mouse embryonic fibroblasts derived from transgenic mice expressing a (TAP) epitope-tagged 14-3-3ζ molecule combined with affinity proteomics to discover that the interactome of TAP-14-3-3ζ is enriched with RNA splicing factors following the induction of adipocyte differentiation (14). Recently, we have determined that the interactome of 14-3-3ζ in adipose tissue is also sensitive to high-fat diet-induced obesity (15). Altogether, these findings demonstrate the usefulness of determining the 14-3-3ζ interactome in identifying novel regulators of adipocyte differentiation or expansion of adipose tissue mass.…”