Adipose microenvironment promotes triple negative breast cancer cell invasiveness and dissemination by producing CCL5

Peroxisome-proliferator-activated receptor γ (PPARγ) regulates glucose and lipid homeostasis, insulin signaling, and adipocyte differentiation. Here, we report the skipping of exon 5 as a legitimate splicing event generating PPARγΔ5, a previously unidentified naturally occurring truncated isoform of PPARγ, which lacks the entire ligand-binding domain. PPARγΔ5 is endogenously expressed in human adipose tissue and, during adipocyte differentiation, lacks ligand-dependent transactivation ability and acts as a dominant-negative isoform reducing PPARγ activity. Ligand-mediated PPARγ activation induces exon 5 skipping in a negative feedback loop, suggesting alternative splicing as a mechanism regulating PPARγ activity. PPARγΔ5 overexpression modifies the PPARγ-induced transcriptional network, significantly impairing the differentiation ability of adipocyte precursor cells. Additionally, PPARγΔ5 expression in subcutaneous adipose tissue positively correlates with BMI in two independent cohorts of overweight or obese and type 2 diabetic patients. From a functional perspective, PPARγΔ5 mimics PPARG dominant-negative mutated receptors, possibly contributing to adipose tissue dysfunction. These findings open an unexplored scenario in PPARG regulation and PPARγ-related diseases.

The nuclear receptor PPARγis a key regulator of adipogenesis, and alterations of its function are associated with different pathological processes related to metabolic syndrome. We recently identified twoPPARGtranscripts encoding dominant negative PPARγisoforms. The existence of differentPPARGvariants suggests that alternative splicing is crucial to modulate PPARγfunction, underlying some underestimated aspects of its regulation. Here we investigatePPARGexpression in different tissues and cells affected in metabolic syndrome and, in particular, during adipocyte differentiation of human mesenchymal stem cells. We defined the transcript-specific expression pattern ofPPARGvariants encoding both canonical and dominant negative isoforms and identified a novelPPARGtranscript,γ1ORF4. Our analysis indicated that, during adipogenesis, the transcription of alternativePPARGvariants is regulated in a time-specific manner through differential usage of distinct promoters. In addition, our analysis describes—for the first time—the differential contribution of three ORF4 variants to this process, suggesting a still unexplored role for these dominant negative isoforms during adipogenesis. Therefore, our results highlight crucial aspects ofPPARGregulation, suggesting the need of further investigation to rule out the differential impact of allPPARGtranscripts in both physiologic and pathologic conditions, such as metabolism-related disorders.

Adipose tissue‐derived mesenchymal stem cells (Ad‐MSC) and platelet derivatives have been used alone or in combination to achieve regeneration of injured tissues. We have tested the effect of platelet‐rich plasma (PRP) on Ad‐MSC and adipocyte function. PRP increased Ad‐MSC viability, proliferation rate and G1‐S cell cycle progression, by at least 7‐, 2‐, and 2.2‐fold, respectively, and reduced caspase 3 cleavage. Higher PRP concentrations or PRPs derived from individuals with higher platelet counts were more effective in increasing Ad‐MSC growth. PRP also accelerated cell migration by at least 1.5‐fold. However, PRP did not significantly affect mature adipocyte viability, differentiation and expression levels of PPAR‐γ and AP‐2 mRNAs, while it increased leptin production by 3.5‐fold. Interestingly, PRP treatment of mature adipocytes also enhanced the release of Interleukin (IL)‐6, IL‐8, IL‐10, Interferon‐γ, and Vascular Endothelial Growth Factor. Thus, data are consistent with a stimulatory effect of platelet derivatives on Ad‐MSC growth and motility. Moreover, PRP did not reduce mature adipocyte survival and increased the release of pro‐angiogenic factors, which may facilitate tissue regeneration processes. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc. J. Cell. Biochem. 116: 2408–2418, 2015. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Glucose impairs tamoxifen responsiveness modulating connective tissue growth factor in breast cancer cells Glucose impairs tamoxifen responsiveness modulating connective tissue growth factor in breast cancer cells