Background Emerging evidence supports the pivotal roles of adipocytes in breast cancer progression. Tumour induced beige/brown adipose tissue differentiation contributes to the hypermetabolic state of the breast cancer. However, the mediators and mechanisms remain unclear. Methods Survival probabilities were estimated using the Kaplan–Meier method based on immunohistochemistry results. Biochemical studies were performed to characterize the novel interrelation between breast cancer cells and adipocytes. Results We show that tumour-surrounding adipocytes exhibit an altered phenotype in terms of upregulated beige/brown characteristics and increased catabolism associated with an activated state characterized by the release of metabolites, including free fatty acids, pyruvate, lactate and ketone bodies. Likewise, tumour cells cocultivated with mature adipocytes exhibit metabolic adaptation and an aggressive phenotype in vitro and in vivo. Mechanistically, we show that tumour cells induce beige/brown differentiation and remodel metabolism in resident adipocytes by exosomes from the co-culture system that carry high levels of miRNA-144 and miRNA-126. miRNA-144 promotes beige/brown adipocyte characteristics by downregulating the MAP3K8/ERK1/2/PPARγ axis, and exosomal miRNA-126 remodels metabolism by disrupting IRS/Glut-4 signalling, activating the AMPK/autophagy pathway and stabilizing HIF1α expression in imminent adipocytes. In vivo inhibition of miRNA-144 or miRNA-126 decreases adipocyte–induced tumour growth. Conclusions These results demonstrate that by inducing beige/brown differentiation and enhancing catabolism in recipient adipocytes, exosomal miRNA-144 and miRNA-126 from the tumour-adipocyte interaction reprogram systemic energy metabolism to facilitate tumour progression. Electronic supplementary material The online version of this article (10.1186/s13046-019-1210-3) contains supplementary material, which is available to authorized users.

APPL1 is a newly identified adiponectin receptor-binding protein that positively mediates adiponectin signaling in cells.Here we report that APPL2, an isoform of APPL1 that forms a dimer with APPL1, can interacts with both AdipoR1 and AdipoR2 and acts as a negative regulator of adiponectin signaling in muscle cells. Overexpression of APPL2 inhibits the interaction between APPL1 and AdipoR1, leading to down-regulation of adiponectin signaling in C2C12 myotubes. In contrast, suppressing APPL2 expression by RNAi significantly enhances adiponectin-stimulated glucose uptake and fatty acid oxidation. In addition to targeting directly to and competing with APPL1 in binding with the adiponectin receptors, APPL2 also suppresses adiponectin and insulin signaling by sequestrating APPL1 from these two pathways. In addition to adiponectin, metformin also induces APPL1-APPL2 dissociation. Taken together, our results reveal that APPL isoforms function as an integrated YinYang regulator of adiponectin signaling and mediate the crosstalk between adiponectin and insulin signaling pathways in muscle cells.Adiponectin, an adipocyte-secreted hormone that regulates energy homeostasis and insulin sensitivity, has been shown to be a promising therapeutic drug target for the treatment of type 2 diabetes (1-3). Adiponectin binds to its membrane receptors (AdipoR1 and AdipoR2) 3 and regulates lipid and glucose metabolism by activating downstream signaling molecules, such as AMP-activated protein kinase (AMPK), p38 MAP kinase (MAPK), and PPAR␣, in the muscle and liver (1, 4). Activation of AMPK by adiponectin reduces S6 kinase-mediated IRS-1 serine phosphorylation and increases IRS-1 tyrosine phosphorylation thus sensitizes insulin signaling in C2C12 myotubes (5), suggesting a direct cross-talk between the adiponectin and insulin signaling pathways.We have recently identified APPL1 (adaptor protein-containing PH domain, PTB domain, and leucine zipper motif) as a signaling protein immediately downstream of adiponectin receptors and positively mediates adiponectin signaling in muscle cells (6). This adaptor protein was previously shown to interact with the catalytic subunit of PI 3-kinase (p110) and Akt, which are two key kinases in the PI 3-kinase pathway downstream of the insulin receptor (7). The interaction between APPL1 and Akt is required for insulin-stimulated GLUT4 translocation (8) and for controlling Akt substrate selectivity (9). It has been shown that APPL1-potentiated Akt activity to suppress androgen receptor transactivation in prostate cancer cells (10). APPL1 has also been suggested to function as an adaptor protein in regulating follicle-stimulated hormone (FSH)-mediated PI 3-kinase/ Akt signaling pathway (11, 12). Our results showed that APPL1 binds directly to the intracellular part of the adiponectin receptors and positively mediates adiponectin signaling to the AMPK and p38 MAPK pathways, leading to increased glucose uptake and fatty acid oxidation in muscle cells (6). In addition, we found that APPL1 plays a critical ro...

Adiponectin functions as an insulin sensitizer, and yet the underlying molecular mechanism(s) remains largely unknown. We found that treating C2C12 myotubes with adiponectin or rapamycin enhanced the ability of insulin to stimulate IRS-1 tyrosine phosphorylation and Akt phosphorylation, concurrently with reduced p70 S6 kinase phosphorylation at Thr 389 as well as IRS-1 phosphorylation at Ser 302 and Ser 636/639 . Overexpression of dominant-negative AMP kinase (AMPK), but not dominant-negative p38 MAPK, reduced the insulin-sensitizing effect of adiponectin. Rapamycin, but not adiponectin, enhanced insulin-stimulated Akt phosphorylation in HeLa cells, which lack LKB1, and exogenous expression of LKB1 in HeLa cells rescued the insulin-sensitizing effect of adiponectin. Finally, overexpression of wild-type Rheb (Ras homology-enriched in brain) or the TSC2 mutant lacking the AMPK phosphorylation site (TSC2 S1345A ) inhibited the insulin-sensitizing effect of adiponectin in C2C12 cells. These results indicate that activation of the LKB1/AMPK/ TSC1/2 pathway alleviates the p70 S6 kinase-mediated negative regulation of insulin signaling, providing a mechanism by which adiponectin increases insulin sensitivity in cells.Adiponectin (Acrp30, AdipoQ, ApM1, and GBP28) is a collagen-like adipokine that has anti-atherogenic, antidiabetic, and insulin-sensitizing properties (1-3). Mice lacking adiponectin have severe hepatic insulin resistance (4), and administration of adiponectin to animal models of type 2 diabetes and insulin resistance significantly enhances insulin sensitivity (5). In humans, adiponectin levels are low in the plasma of obese and type 2 diabetes subjects (6 -8). The combined data suggest that adiponectin plays an important role in sensitizing insulin action.The molecular mechanism by which adiponectin acts as an insulin sensitizer remains largely unknown. Insulin initiates its action by binding to its membrane receptor, leading to tyrosine phosphorylation and activation of the insulin receptor (IR).2 A major pathway downstream of IR is the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which mediates insulinstimulated GLUT4 membrane translocation and glucose uptake. Recent studies have shown that the PI3K pathway is negatively regulated by the TOR complex 1 (TORC1)-induced signaling pathway, which is mediated by the S6K-dependent phosphorylation of IRS-1 at several sites including Ser 302 , Ser 307 , and Ser 636/639 (9 -12). The inhibitory effect of S6K is greatly enhanced in cells lacking the tuberous sclerosis complex (TSC1/2), suggesting that TSC1/2 is a negative regulator of the mTOR/S6K signaling pathway (13). Interestingly, TSC1/2 activity is stimulated by AMP kinase (AMPK) (14), a heterotrimeric serine/threonine protein kinase, which is activated by adiponectin (15). However, whether activation of AMPK by adiponectin leads to inhibition of S6K and whether this inhibition plays a role in the insulin sensitizing effect of adiponectin remain unknown.In the present study, we have shown that adip...

SUMMARYBinding of insulin receptor substrate proteins 1 and 2 (IRS1/2) to the insulin receptor (IR) is essential for the regulation of insulin sensitivity and energy homeostasis. However, the mechanism of IRS1/2 recruitment to the IR remains elusive. Here, we identify adaptor protein APPL1 as a critical molecule that promotes IRS1/2-IR interaction. APPL1 forms a complex with IRS1/2 under basal conditions, and this complex is then recruited to the IR in response to insulin or adiponectin stimulation. The interaction between APPL1 and IR depends on insulin- or adiponectin-stimulated APPL1 phosphorylation, which is greatly reduced in insulin target tissues in obese mice. appl1 deletion in mice consistently leads to systemic insulin resistance and a significant reduction in insulin-stimulated IRS1/2, but not IR, tyrosine phosphorylation, indicating that APPL1 sensitizes insulin signaling by acting at a site downstream of the IR. Our study uncovers a mechanism regulating insulin signaling and crosstalk between the insulin and adiponectin pathways.

Previous studies have evidenced that the anticancer potential of curcumin (diferuloylmethane), a main yellow bioactive compound from plant turmeric was mediated by interfering with PI3K/Akt signaling. However, the underlying molecular mechanism is still poorly understood. This study experimentally revealed that curcumin treatment reduced Akt protein expression in a dose- and time-dependent manner in MDA-MB-231 breast cancer cells, along with an activation of autophagy and suppression of ubiquitin-proteasome system (UPS) function. The curcumin-reduced Akt expression, cell proliferation, and migration were prevented by genetic and pharmacological inhibition of autophagy but not by UPS inhibition. Additionally, inactivation of AMPK by its specific inhibitor compound C or by target shRNA-mediated silencing attenuated curcumin-activated autophagy. Thus, these results indicate that curcumin-stimulated AMPK activity induces activation of the autophagy-lysosomal protein degradation pathway leading to Akt degradation and the subsequent suppression of proliferation and migration in breast cancer cell.