Cyclin D3 promotes adipogenesis through activation of peroxisome proliferator-activated receptor gamma
Authors: Said Assou
David A Sarruf
Irena Iankova
Anna Abella
Lluis Fajas
St√©phanie Miard
Journal: Molecular and Cellular Biology (2005)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: D-type cyclins; transcriptional regulation; cellular differentiation; adipogenesis; cyclin D3
Affiliations: INSERM, Equipe Avenir, U540, 60, rue de Navacelles, F34090 Montpellier, France.

Abstract:  In addition to their role in cell cycle progression, new data reveal an emerging role of D-type cyclins in transcriptional regulation and cellular differentiation processes. Using 3T3-L1 cell lines to study adipogenesis, we observed an up-regulation of cyclin D3 expression throughout the differentiation process. Surprisingly, cyclin D3 was only minimally expressed during the initial stages of adipogenesis, when mitotic division is prevalent. This seemingly paradoxical expression led us to investigate a potential cell cycle-independent role for cyclin D3 during adipogenesis. We show here a direct interaction between cyclin D3 and the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Our experiments reveal cyclin D3 acts as a ligand-dependent PPARgamma coactivator, which, together with its cyclin-dependent kinase partner, phosphorylates the A-B domain of the nuclear receptor. Overexpression and knockdown studies with cyclin D3 had marked effects on PPARgamma activity and subsequently on adipogenesis. Chromatin immunoprecipitation assays confirm the participation of cyclin D3 in the regulation of PPARgamma target genes. We show that cyclin D3 mutant mice are protected from diet-induced obesity, display smaller adipocytes, have reduced adipogenic gene expression, and are insulin sensitive. Our results indicate that cyclin D3 is an important factor governing adipogenesis and obesity. 

Retracted: No

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 Good morning, This is Lluis Fajas, the last author of this paper. First of all, I am sorry for the delayed reply. Second, I feel very uncomfortable not knowing with whom I am discussing. And third, letu2019s go to the subject. This image represents a GST pull down assay using in vitro translated cyclin D3 and purified GST or GST-PPARg fusion protein to test their interaction, which is obviously there. This is not a quantitative test. There is nothing else to prove here. Concerning the similar background, it is definitely very similar. Indeed, the original image was probably coming with a u201cdirtyu201d background because of radioactivity. Instead of decreasing light or increasing contrast (which was a common way to improve the printed quality of the images), the buffer tool was used to remove spots and other non-relevant signals. Unfortunately, I could not find the original blot so far, though I am still trying. I also want to address the other subject that has been raised, regarding the PPARg western blot that is shared with other papers. This blot is coming from a unique and very clean experiment of preadipocyte differentiation. In this experiment the samples were collected and blotted against several proteins involved in cell cycle, including cyclin D3, cyclin A, cyclin E, E2F1, E2F4. The aim was to analyze the participation of these proteins in the differentiation process. The expression of PPARg was only used as a control of differentiation. In each individual paper, the expression of the concerned protein is shown, together with the control (PPARg). Please let me insist, all the blots shown in the different papers are the same experiment. This is the reason why the PPARg blot (common to all) is shown several times. ,