ABSTRACT
Aberrant leptin signaling and overexpression of fibroblast growth factor receptor 1 (FGFR1) are both implicated in the pathogenesis of letrozole resistance in breast cancer (BCa), but it remains unknown whether these two pathways are involved in letrozole resistance in a coordinated manner. Here, we demonstrate that expression levels of the pre-B-cell leukemia homeobox transcription factor 3 (PBX3), a pioneer factor that governs divergent biological processes, were significantly upregulated in letrozole-resistant BCa cells and tissues, and this upregulation correlated to a poorer progression-free survival in patients. By leveraging a patient-derived xenograft model with pharmacological approaches, we demonstrated that leptin activated PBX3 expression in a STAT3 (signal transducer and activator of transcription 3)-dependent manner. Our loss- and gain-of-function study further showed that PBX3 attenuated response to letrozole by potentiating BCa cell survival and anchorage-independent growth in BCa cells. By profiling BCa cells with ectopic PBX3 expression, we revealed that PBX3 conferred letrozole resistance via transactivation of the FGFR1 signaling, and this molecular event must coordinate a synergistic transcription activation programs through interacting with MTA1-HDAC2 (metastasis associated 1-histone deacetylase 2) complex. Overall, the available data reveal a novel role of leptin/PBX3 cascade linking energy homeostasis (i.e. hyperleptinemia) and endocrine therapy failure (i.e. letrozole resistance) in BCa.
ABSTRACT
OBJECTIVE: To observe the effect of electroacupuncture (EA) of "Zusanli" (ST 36) on mitochondrial oxidative stress of skeletal muscle in rats with chronic fatigue syndrome (CFS) based on adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)/ peroxlsome proliferator-activated receptor-γ coactivator-1 α (PGC-1 α) signaling, in order to reveal its mechanism underlying improvement of CFS. METHODS: Forty SD rats were randomly divided into normal control, CFS model, EA-Zusanli (ST 36) and EA-non-acupoint groups (n=10 rats in each group). The CFS model was established by forced exhausted load-bearing swimming (twice daily), chronic constraint (1 h) and sleep deprivation (20 h/day) for 14 days. Following modeling, EA (2 Hz/100 Hz, 2 V) was applied to bilateral Zusanli (ST 36) or non-acupoint (about 10-15 mm superior to the bilateral Iliac creast and about 20 mm lateral to the posterior median line) for 20 min, once a day for 10 days. The expression levels of ATP synthase, AMPK, phosphorylated (p)-AMPK, silent mating type information regulation 2 homolog-1 (SIRT 1) and PGC-1 α proteins, and ATP synthase, SIRT 1 and PGC-1 α mRNAs of the quadriceps femoris muscle were detected by Western blot and fluorescence quantitative PCR, respectively. The rats' grabbing force was detected by using a grabbing-force detector. RESULTS: Compared with the normal group, the grabbing force, and the expression levels of ATP synthase and PGC-1 α proteins and mRNAs were significantly decreased (P<0.05, P<0.01), while the expression of SIRT 1 protein was significantly up-regulated (P<0.05) in the CFS model group. Following EA intervention, the grabbing force and the expression levels of ATP synthase mRNA, SIRT 1 and PGC-1 α proteins and mRNAs, and p-AMPK/AMPK were significantly up-regulated in the EA-Zusanli (ST 36) group (P<0.05, P<0.01). CONCLUSION: EA of ST 36 can raise the grabbing force of CFS rats, which may be related to its effects in up-regulating the expression of ATP synthase mRNA, SIRT 1 and PGC-1 α proteins and mRNAs, and p-AMPK/AMPK to reduce mitochondrial oxidative stress reaction and in increasing ATP synthesis.
