Prostate cancer (PCa) commonly metastasizes to the bone where the cells frequently undergo dormancy. The escape of disseminated tumor cells from cellular dormancy is a major cause of recurrence in marrow. Abscisic acid (ABA), a phytohormone, is known to regulate dormancy of plant seeds and to regulate other stress responses in plants. Recently, ABA was found to be synthesized by mammals cells and has been linked to human disease. Yet the role of ABA in regulating tumor dormancy or reactivation is unknown. We found that ABA is produced by human marrow cells, and exogenous ABA inhibits PCa cell proliferation while increasing the expression of p27, p21, and p16 and decreasing the expression of the proliferation marker, Ki67. Further, ABA significantly increased the percentage of PCa cells in the G0 phase of the cell cycle as well as the duration the cells were arrested in G0. We found that ABA regulates an increase of PPARγ receptor expression and suppressed phosphorylation of mTOR/p70S6K signaling and resulting in the induction of the cellular dormancy. We then confirmed that ABA regulates G0 cell cycle arrest through PPARγ receptor signaling in vitro and under co-culture conditions with osteoblasts. Finally, we demonstrate that ABA regulates PCa dormancy in vivo following intratibial injection in an animal model. Together these data suggest that the ABA and PPARγ signaling pathways contribute to the establishment of PCa cellular dormancy in the bone marrow microenvironment. These findings may suggest critical pathways for targeting metastatic disease.
<p>Supplemental Figure 1: Small cell carcinoma in PCa patient tissues. Supplemental Figure 2: Metastatic potential of CXCL12 γ expression in PCa cells and CXCL12 γ expression in normal human and mouse tissues. Supplemental Figure 3: CXCL12 γ induces CSCs, which promotes BCa tumor growth. Supplemental Figure 4: CXCL12 γ induces a NE phenotype in BCa cells. Supplemental Figure 5: Regression analyses of ENO2 mRNA expression and serum Enolase 2/NSE, Chromogranin A, and PSA in m-CRPC patients. Supplemental Figure 6: CSCs in NE PCa cells and The role of CXCL12 γ in AR-dependent PCa cells. Supplemental Figure 7: CXCL12 γ contributes activation of CXCR4-mediated PKC α /NF κ B signaling in CSC and NE inductions in BCa cells.</p>
Exposure of astronauts in space to radiation during weightlessness may contribute to subsequent bone loss. Gamma irradiation of postpubertal mice rapidly increases the number of bone-resorbing osteoclasts and causes bone loss in cancellous tissue; similar changes occur in skeletal diseases associated with oxidative stress. Therefore, we hypothesized that increased oxidative stress mediates radiation-induced bone loss and that musculoskeletal disuse changes the sensitivity of cancellous tissue to radiation exposure. Musculoskeletal disuse by hindlimb unloading (1 or 2 wk) or total body gamma irradiation (1 or 2 Gy of (137)Cs) of 4-mo-old, male C57BL/6 mice each decreased cancellous bone volume fraction in the proximal tibiae and lumbar vertebrae. The extent of radiation-induced acute cancellous bone loss in tibiae and lumbar vertebrae was similar in normally loaded and hindlimb-unloaded mice. Similarly, osteoclast surface in the tibiae increased 46% as a result of irradiation, 47% as a result of hindlimb unloading, and 64% as a result of irradiation + hindlimb unloading compared with normally loaded mice. Irradiation, but not hindlimb unloading, reduced viability and increased apoptosis of marrow cells and caused oxidative damage to lipids within mineralized tissue. Irradiation also stimulated generation of reactive oxygen species in marrow cells. Furthermore, injection of alpha-lipoic acid, an antioxidant, mitigated the acute bone loss caused by irradiation. Together, these results showed that disuse and gamma irradiation, alone or in combination, caused a similar degree of acute cancellous bone loss and shared a common cellular mechanism of increased bone resorption. Furthermore, irradiation, but not disuse, may increase the number of osteoclasts and the extent of acute bone loss via increased reactive oxygen species production and ensuing oxidative damage, implying different molecular mechanisms. The finding that alpha-lipoic acid protected cancellous tissue from the detrimental effects of irradiation has potential relevance to astronauts and radiotherapy patients.
The proliferation-quiescence decision is a dynamic process that remains incompletely understood. Live-cell imaging with fluorescent cell cycle sensors now allows us to visualize the dynamics of cell cycle transitions and has revealed that proliferation-quiescence decisions can be highly heterogeneous, even among clonal cell lines in culture. Under normal culture conditions, cells often spontaneously enter non-cycling G0 states of varying duration and depth. This also occurs in cancer cells and G0 entry in tumors may underlie tumor dormancy and issues with cancer recurrence. Here we show that a cell cycle indicator previously shown to indicate G0 upon serum starvation, mVenus-p27K-, can also be used to monitor spontaneous quiescence in untransformed and cancer cell lines. We find that the duration of spontaneous quiescence in untransformed and cancer cells is heterogeneous and that a portion of this heterogeneity results from asynchronous proliferation-quiescence decisions in pairs of daughters after mitosis, where one daughter cell enters or remains in temporary quiescence while the other does not. We find that cancer dormancy signals influence both entry into quiescence and asynchronous proliferation-quiescence decisions after mitosis. Finally, we show that spontaneously quiescent prostate cancer cells exhibit altered expression of components of the Hippo pathway and are enriched for the stem cell markers CD133 and CD44. This suggests a hypothesis that dormancy signals could promote cancer recurrence by increasing the proportion of quiescent tumor cells poised for cell cycle re-entry with stem cell characteristics in cancer.
Cancer metastasis is a multistep process associated with the induction of an epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs). Although significant progress has been made in understanding the molecular mechanisms regulating EMT and the CSC phenotype, little is known of how these processes are regulated by epigenetics. Here we demonstrate that reduced expression of DNA methyltransferase 1 (DNMT1) plays an important role in the induction of EMT and the CSC phenotype by prostate cancer (PCa) cells, with enhanced tumorigenesis and metastasis. First, we observed that reduction of DNMT1 by 5-azacitidine (5-Aza) promotes EMT induction as well as CSCs and sphere formation in vitro. Reduced expression of DNMT1 significantly increased PCa migratory potential. We showed that the increase of EMT and CSC activities by reduction of DNMT1 is associated with the increase of protein kinase C. Furthermore, we confirmed that silencing DNMT1 is correlated with enhancement of the induction of EMT and the CSC phenotype in PCa cells. Additionally, chromatin immunoprecipitation assay reveals that reduction of DNMT1 promotes the suppression of H3K9me3 and H3K27me3 on the Zeb2 and KLF4 promoter region in PCa cells. Critically, we found in an animal model that significant tumor growth and more disseminated tumor cells in most osseous tissues were observed following injection of 5-Aza pretreated–PCa cells compared with vehicle-pretreated PCa cells. Our results suggest that epigenetic alteration of histone demethylation regulated by reduction of DNMT1 may control induction of EMT and the CSC phenotype, which facilitates tumorigenesis in PCa cells and has important therapeutic implications in targeting epigenetic regulation.
We review here regarding the observations that expression of osteopontin (OPN) was enhanced in the joints of rheumatoid arthritis patients. OPN in arthritic joints had not been clear previously. We published in 2002 that joint destruction in the arthritis model induced by a mixture of anti-type II collagen monoclonal antibodies and LPS (mAbs/LPS) injection was suppressed in the OPN-deficient mice. OPN is a phosphorylated glycoprotein interacts with integrins and CD44, promote the cell attachment and migration. OPN is highly expressed in bone, kidney and ovary and also produced by osteoclasts, endotherial cells, activated T cells and macrophages. One of the functions of OPN in the inflammatory condition is to bring inflammatory cells to the sites of injury and OPN is also a survival factor for the endotherial cells and enhances angiogenesis by promoting the vascular tube formation. Infiltration of inflammatory cells and angiogenesis in synovium in the arthritis model was suppressed in OPN-deficient mice. Additionally, apoptosis of chondrocytes in articular cartilage was reduced and destruction of articular cartilage was suppressed in the arthritis model in OPN-deficient mice. These data suggested that OPN might be a new target for the treatment of rheumatoid arthritis.
