Breast cancer bone micrometastases can remain asymptomatic for years before progressing into overt lesions. The biology of this process, including the microenvironment niche and supporting pathways, ...is unclear. We find that bone micrometastases predominantly reside in a niche that exhibits features of osteogenesis. Niche interactions are mediated by heterotypic adherens junctions (hAJs) involving cancer-derived E-cadherin and osteogenic N-cadherin, the disruption of which abolishes niche-conferred advantages. We elucidate that hAJ activates the mTOR pathway in cancer cells, which drives the progression from single cells to micrometastases. Human data set analyses support the roles of AJ and the mTOR pathway in bone colonization. Our study illuminates the initiation of bone colonization, and provides potential therapeutic targets to block progression toward osteolytic metastases.
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•Intrailiac artery injection allows studies of bone metastasis initiation•Bone micrometastases reside in the microenvironment niche with active osteogenesis•The niche cells boost tumor proliferation via adherens junctions (AJs)•The mTOR pathway lies downstream of AJs and mediates metastasis initiation
Wang et al. model breast cancer bone micrometastasis and identify an osteogenic niche that supports this process. Heterotypic adherens junctions form between cancer cells and stromal cells in these niches and activate mTOR to promote micrometastasis progression.
Osteocytes are the terminally differentiated cell type of the osteoblastic lineage and have important functions in skeletal homeostasis. Although the transcriptional regulation of osteoblast ...differentiation has been well characterized, the factors that regulate differentiation of osteocytes from mature osteoblasts are poorly understood. Here we show that miR-23a∼27a∼24-2 (miR-23a cluster) promotes osteocyte differentiation. Osteoblast-specific miR-23a cluster gain-of-function mice have low bone mass associated with decreased osteoblast but increased osteocyte numbers. By contrast, loss-of-function transgenic mice overexpressing microRNA decoys for either miR-23a or miR-27a, but not miR24-2, show decreased osteocyte numbers. Moreover, RNA-sequencing analysis shows altered transforming growth factor-β (TGF-β) signalling. Prdm16, a negative regulator of the TGF-β pathway, is directly repressed by miR-27a with concomitant alteration of sclerostin expression, and pharmacological inhibition of TGF-β rescues the phenotypes observed in the gain-of-function transgenic mice. Taken together, the miR-23a cluster regulates osteocyte differentiation by modulating the TGF-β signalling pathway through targeting of Prdm16.
Osteogenic sarcoma (OS) is a deadly skeletal malignancy whose cause is unknown. We report here a mouse model of OS based on conditional expression of the intracellular domain of Notch1 (NICD). ...Expression of the NICD in immature osteoblasts was sufficient to drive the formation of bone tumors, including OS, with complete penetrance. These tumors display features of human OS; namely, histopathology, cytogenetic complexity, and metastatic potential. We show that Notch activation combined with loss of p53 synergistically accelerates OS development in mice, although p53-driven OS is not Rbpj dependent, which demonstrates a dual dominance of the Notch oncogene and p53 mutation in the development of OS. Using this model, we also reveal the osteoblasts as the potential sources of OS.
•Notch 1 intracellular domain induces bone tumors in mice with 100% penetrance•Mouse osteosarcoma initiated by Notch activation mimics the human disease•Notch activation and p53 loss independently and synergistically induce osteosarcoma•Committed osteoblasts are a potential source of tumor cells in osteosarcomagenesis
Tao et al. show that Notch activation in osteoblasts is sufficient to initiate osteogenic sarcoma (OS)-like tumors that mimic human OS and demonstrate a dual dominance for Notch activation and p53 mutation in the development of OS.
Notch signaling is an evolutionarily conserved mechanism for specifying and regulating organogenesis and tissue renewal. Human and mouse genetic studies have demonstrated mutations in many components ...of the Notch signaling pathway that cause skeletal patterning defects. More recently, the in vivo effects of Notch signaling on osteoblast specification, proliferation, and differentiation have been demonstrated in addition to its regulation of osteoclast activity. However, while our understanding of canonical Notch signaling in skeletal biology is rapidly evolving, the role of noncanonical Notch signaling is still poorly understood. In a pathologic context, aberration of Notch signaling is also associated with osteosarcoma. These studies raise the question of how Notch may interact with other signaling pathways, such as Wnt. Finally, manipulation of Notch signaling for bone‐related diseases remains complex because of the temporal and context‐dependent nature of Notch signaling during mesenchymal stem cell and osteoblast differentiation.
Key points
This study demonstrates and evaluates the changes in rat vascular smooth muscle cell biomechanics following statin‐mediated cholesterol depletion.
Evidence is presented to show correlated ...changes in migration and adhesion of vascular smooth muscle cells to extracellular matrix proteins fibronectin and collagen. Concurrently, integrin α5 expression was enhanced but not integrin α2.
Atomic force microscopy analysis provides compelling evidence of coordinated reduction in vascular smooth muscle cell stiffness and actin cytoskeletal orientation in response to statin‐mediated cholesterol depletion.
Proof is provided that statin‐mediated cholesterol depletion remodels total vascular smooth muscle cell cytoskeletal orientation that may additionally participate in altering ex vivo aortic vessel function.
It is concluded that statin‐mediated cholesterol depletion may coordinate vascular smooth muscle cell migration and adhesion to different extracellular matrix proteins and regulate cellular stiffness and cytoskeletal orientation, thus impacting the biomechanics of the cell.
Not only does cholesterol induce an inflammatory response and deposits in foam cells at the atherosclerotic plaque, it also regulates cellular mechanics, proliferation and migration in atherosclerosis progression. Statins are HMG‐CoA reductase inhibitors that are known to inhibit cellular cholesterol biosynthesis and are clinically prescribed to patients with hypercholesterolemia or related cardiovascular conditions. Nonetheless, the effect of statin‐mediated cholesterol management on cellular biomechanics is not fully understood. In this study, we aimed to assess the effect of fluvastatin‐mediated cholesterol management on primary rat vascular smooth muscle cell (VSMC) biomechanics. Real‐time measurement of cell adhesion, stiffness, and imaging were performed using atomic force microscopy (AFM). Cellular migration on extra cellular matrix (ECM) protein surfaces was studied by time‐lapse imaging. The effect of changes in VSMC biomechanics on aortic function was assessed using an ex vivo myograph system. Fluvastatin‐mediated cholesterol depletion (‐27.8%) lowered VSMC migration distance on a fibronectin (FN)‐coated surface (‐14.8%) but not on a type 1 collagen (COL1)‐coated surface. VSMC adhesion force to FN (+33%) and integrin α5 expression were enhanced but COL1 adhesion and integrin α2 expression were unchanged upon cholesterol depletion. In addition, VSMC stiffness (‐46.6%) and ex vivo aortic ring contraction force (‐40.1%) were lowered and VSMC actin cytoskeletal orientation was reduced (‐24.5%) following statin‐mediated cholesterol depletion. Altogether, it is concluded that statin‐mediated cholesterol depletion may coordinate VSMC migration and adhesion to different ECM proteins and regulate cellular stiffness and cytoskeletal orientation, thus impacting the biomechanics of the cell and aortic function.
Key points
This study demonstrates and evaluates the changes in rat vascular smooth muscle cell biomechanics following statin‐mediated cholesterol depletion.
Evidence is presented to show correlated changes in migration and adhesion of vascular smooth muscle cells to extracellular matrix proteins fibronectin and collagen. Concurrently, integrin α5 expression was enhanced but not integrin α2.
Atomic force microscopy analysis provides compelling evidence of coordinated reduction in vascular smooth muscle cell stiffness and actin cytoskeletal orientation in response to statin‐mediated cholesterol depletion.
Proof is provided that statin‐mediated cholesterol depletion remodels total vascular smooth muscle cell cytoskeletal orientation that may additionally participate in altering ex vivo aortic vessel function.
It is concluded that statin‐mediated cholesterol depletion may coordinate vascular smooth muscle cell migration and adhesion to different extracellular matrix proteins and regulate cellular stiffness and cytoskeletal orientation, thus impacting the biomechanics of the cell.
Abstract Osteosarcoma is the predominant form of bone cancer, affecting mostly adolescents. Recent progress made in molecular genetic studies of osteosarcoma has changed our view on the cause of the ...disease and ongoing therapeutic approaches for patients. As we draw closer to gaining more complete
catalogs
of candidate cancer driver genes in common forms of cancer, the landscape of somatic mutations in osteosarcoma is emerging from its first phase. In this review, we summarize recent whole genome and/or whole exome genomic studies, and then put these findings in the context of genetic hallmarks of somatic mutations and mutational processes in human osteosarcoma. One of the lessons learned here is that the extent of somatic mutations and complexity of the osteosarcoma genome are similar to that of common forms of adult cancer. Thus, a much higher number of samples than those currently obtained are needed to complete the
catalog
of driver mutations in human osteosarcoma. In parallel, genetic studies in other species have revealed candidate driver genes and their roles in the genesis of osteosarcoma. This review also summarizes newly identified drivers in genetically engineered mouse models (GEMMs) and discusses our understanding of the impact of nature and number of drivers on tumor latency, subtypes, and metastatic potentials of osteosarcoma. It is becoming apparent that a synergistic team composed of three drivers (one ‘first driver’ and two ‘synergistic drivers’) may be required to generate an animal model that recapitulates aggressive osteosarcoma with a short latency. Finally, new cancer therapies are urgently needed to improve survival rate and quality of life for osteosarcoma patients. Several vulnerabilities in osteosarcoma are illustrated in this review to exemplify the opportunities for next generation molecularly targeted therapies. However, much work remains in order to complete our understanding of the somatic mutation basis of osteosarcoma, to develop reliable animal models of human disease, and to apply this information to guide new therapeutic approaches for reducing morbidity and mortality of this rare disease.
Dysregulation of histone deacetylases (HDACs) is associated with the pathogenesis of human osteosarcoma, which may present an epigenetic vulnerability as well as a therapeutic target. Domatinostat ...(4SC-202) is a next-generation class I HDAC inhibitor that is currently being used in clinical research for certain cancers, but its impact on human osteosarcoma has yet to be explored. In this study, we report that 4SC-202 inhibits osteosarcoma cell growth in vitro and in vivo. By analyzing cell function in vitro, we show that the anti-tumor effect of 4SC-202 involves the combined induction of cell-cycle arrest at the G2/M phase and apoptotic program, as well as a reduction in cell invasion and migration capabilities. We also found that 4SC-202 has little capacity to promote osteogenic differentiation. Remarkably, 4SC-202 revised the global transcriptome and induced distinct signatures of gene expression in vitro. Moreover, 4SC-202 decreased tumor growth of established human tumor xenografts in immunodeficient mice in vivo. We further reveal key targets regulated by 4SC-202 that contribute to tumor cell growth and survival, and canonical signaling pathways associated with progression and metastasis of osteosarcoma. Our study suggests that 4SC-202 may be exploited as a valuable drug to promote more effective treatment of patients with osteosarcoma and provide molecular insights into the mechanism of action of class I HDAC inhibitors.
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