Kassem, M. | Search bioRxiv

bioRxiv2022

GIP receptor reduces osteoclast activity and improves osteoblast survival by activating multiple signaling pathways

Bone is a dynamic tissue that is remodeled throughout life by bone resorbing osteoclasts and bone forming osteoblasts, to adapt to physiological or mechanical demands. These processes are impaired in osteoporosis, and understanding how bone remodeling is regulated could improve anti-osteoporotic treatments. Clinical investigations show that short-term treatment with glucose-dependent insulinotropic polypeptide (GIP) acutely decreases serum markers of bone resorption and may increase bone formation. However, evidence for direct effects of GIP intracellular signaling and functions in mature human osteoclasts and osteoblasts have not been investigated. We report that the GIP receptor (GIPR) is robustly expressed in mature human osteoclasts. Exposure of osteoclasts to GIP inhibits osteoclastogenesis, delays bone resorption, and increases osteoclast apoptosis by acting upon multiple signaling pathways (cAMP, Src, Akt, calcium, p38) to impair nuclear translocation of nuclear factor of activated T cells 1 (NFATc1) and nuclear factor-{kappa}B (NF{kappa}B). Human osteoblasts also express GIPR, and GIP improves osteoblast survival via cAMP and Akt-mediated pathways. GIP treatment of co-cultures of osteoclasts and osteoblasts also decreased bone resorption. Antagonizing GIPR with GIP(3-30)NH2 abolished the effects of GIP on osteoclasts and osteoblasts. This study demonstrates that GIP inhibits bone resorption and improves survival of human osteoblasts, which could increase bone mass and strength, supporting clinical investigations of the effect of GIP on bone. Moreover, this study demonstrates that GIPR agonism could be beneficial in the treatment of disorders of bone remodeling, such as osteoporosis. One-sentence SummaryGIP acts directly on bone cells to regulate bone remodeling

cell biology↗

bioRxiv2022

Activity of Estrogen Receptor β Agonists in Therapy-Resistant Estrogen Receptor-Positive Breast Cancer

BackgroundAmong women, breast cancer is the leading cause of cancer-related death worldwide. Estrogen receptor positive (ER+) breast cancer accounts for 70% of all breast cancer subtypes. Although ER+ breast cancer initially responds to estrogen deprivation or blockade, resistance emergence compelling the use of more aggressive therapies. While ER is a driver in ER+ breast cancer, ER{beta} plays an inhibitory role in several different cancer types. To date, the lack of highly selective ER{beta} agonists without ER activity has limited the exploration of ER{beta} activation as a strategy for ER+ breast cancer. MethodsWe measured expression levels of ESR1 and ESR2 genes in immortalized mammary epithelial cells and different breast cancer cell lines. The viability of ER+ breast cancer cell lines upon treatments with specific ER{beta} agonists, including OSU-ERb-12 and LY500307 was assessed. The specificity of the ER{beta} agonists, OSU-ERb-12 and LY500307, was confirmed by reporter assays. The effects of the agonists on cell proliferation, cell cycle, apoptosis, colony formation, cell migration, and expression of tumor suppressor proteins were analyzed. The expression of ESR2 and genes containing ERE-AP1 composite response elements was examined in ER+ human breast cancer samples to determine the correlation between ESR2 expression and overall survival and that of putative ESR2 regulated genes. ResultsIn this study, we demonstrate the efficacy of highly selective ER{beta} agonists in ER+ breast cancer cell lines and drug-resistant derivatives. ER{beta} agonists blocked cell proliferation, migration and colony formation; and induced apoptosis and S and/or G2/M cell cycle arrest of ER+ breast cancer cell lines. Also, increases in the expression of the key tumor suppressors FOXO1 and FOXO3a were noted. Importantly, the strong synergy between ER{beta} agonists and ER antagonists suggested that the efficacy of ER{beta} agonists is maximized by combination with ER blockade. Lastly, ESR2 (ER{beta} gene) expression was negatively correlated with ESR1 (ER gene) and CCND1 RNA expression in human metastatic ER+/HER2-breast cancer samples. ConclusionOur results demonstrate that highly selective ER{beta} agonists attenuate the viability of ER+ breast cancer cell lines in vitro and suggest that this therapeutic strategy merits further evaluation for ER+ breast cancer.

cancer biology↗