A Concerted Kinase Interplay Identifies PPARγ as a Molecular Target of Ghrelin Signaling in Macrophages

The peroxisome proliferator-activator receptor PPARγ plays an essential role in vascular biology, modulating macrophage function and atherosclerosis progression. Recently, we have described the beneficial effect of combined activation of the ghrelin/GHS-R1a receptor and the scavenger receptor CD36 to induce macrophage cholesterol release through transcriptional activation of PPARγ. Although the interplay between CD36 and PPARγ in atherogenesis is well recognized, the contribution of the ghrelin receptor to regulate PPARγ remains unknown. Here, we demonstrate that ghrelin triggers PPARγ activation through a concerted signaling cascade involving Erk1/2 and Akt kinases, resulting in enhanced expression of downstream effectors LXRα and ABC sterol transporters in human macrophages. These effects were associated with enhanced PPARγ phosphorylation independently of the inhibitory conserved serine-84. Src tyrosine kinase Fyn was identified as being recruited to GHS-R1a in response to ghrelin, but failure of activated Fyn to enhance PPARγ Ser-84 specific phosphorylation relied on the concomitant recruitment of docking protein Dok-1, which prevented optimal activation of the Erk1/2 pathway. Also, substitution of Ser-84 preserved the ghrelin-induced PPARγ activity and responsiveness to Src inhibition, supporting a mechanism independent of Ser-84 in PPARγ response to ghrelin. Consistent with this, we found that ghrelin promoted the PI3-K/Akt pathway in a Gαq-dependent manner, resulting in Akt recruitment to PPARγ, enhanced PPARγ phosphorylation and activation independently of Ser-84, and increased expression of LXRα and ABCA1/G1. Collectively, these results illustrate a complex interplay involving Fyn/Dok-1/Erk and Gαq/PI3-K/Akt pathways to transduce in a concerted manner responsiveness of PPARγ to ghrelin in macrophages

Taxanes: optimizing adjuvant chemotherapy for early-stage breast cancer.

Taxanes are among the most widely used chemotherapy agents for advanced breast cancer. Results are now available from 21 trials that randomly allocated nearly 36,000 women with early-stage breast cancer to receive first-generation taxane-based adjuvant chemotherapy versus non-taxane-based adjuvant regimens. Three recent meta-analyses suggest that taxanes are beneficial in the adjuvant setting, irrespective of the patient's age, lymph-node involvement, hormone-receptor expression, and HER2 status. Nevertheless, the optimal role for taxanes in the adjuvant management of early-stage breast cancer remains controversial. We review the results of the first-generation taxane trials and discuss possible explanations for the differences observed in these studies, including variation in the 'strength' of anthracycline therapy in the control arms; suboptimal timing, dosing, or schedule of the taxane regimen; a masking effect of trials that included patients with relatively chemotherapy-insensitive luminal A disease; and decreased representation of the putative taxane-sensitive disease subset. Inclusion criteria for future clinical trials must be revised to account for the molecular heterogeneity of breast cancer and further optimize the role of adjuvant taxane therapy in early-stage disease.Journal Articleinfo:eu-repo/semantics/publishe