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

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.