p38 MAPK comprises four unique isoforms (p38by stimulating the differentiation and proliferation of osteoblasts through a Cbfa-1-dependent pathway.38 C4-2B cells promote mixed osteolytic and osteoblastic lesions by the expression of Wnts and BMPs, which directly promote osteoblastogenesis and indirectly promote osteoclastogenesis.35, 39 Similarly, DU145 cells KB-R7943 mesylate also promote the formation of mixed lesions This highlights a key role of the levels of the Wnt inhibitor DKK-1 in regulating the KB-R7943 mesylate osteoblastic/osteolytic appearance of prostate cancer bone metastases. with siRNA revealed a stronger role for MAPK11 than MAPK14 and MAPK12 in the regulation of DKK-1. Moreover, prostate cancer cells with a predominantly osteolytic phenotype produced sufficient amounts of DKK-1 to inhibit Wnt3a-induced osteoblastic differentiation in C2C12 cells. This inhibition was blocked directly by neutralizing DKK-1 using a specific antibody and also indirectly by blocking p38 MAPK. Furthermore, tissue expression in human prostate cancer revealed a correlation between p38 MAPK and DKK-1 expression with higher expression in tumor compared with normal tissues. These results reveal that p38 MAPK regulates DKK-1 in prostate cancer and may present a potential target in osteolytic prostate cancers. Prostate cancer is the leading cause of cancer-related death in men, second only to lung cancer.1 The survival rate for local and regional stages at diagnosis is close to 100% after 5 years; however, this drops to 30% in the case of advanced disease at diagnosis where the cancer has spread to distal lymph nodes, the bones or other organs.2 Bone metastases, in particular, exhibit in an increased state of morbidity characterized by skeletal-related events, including pathological fractures and spinal cord Rabbit polyclonal to ACC1.ACC1 a subunit of acetyl-CoA carboxylase (ACC), a multifunctional enzyme system.Catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the rate-limiting step in fatty acid synthesis.Phosphorylation by AMPK or PKA inhibits the enzymatic activity of ACC.ACC-alpha is the predominant isoform in liver, adipocyte and mammary gland.ACC-beta is the major isoform in skeletal muscle and heart.Phosphorylation regulates its activity. compression, which considerably reduce a patient’s quality of life.3, 4 Bone metastases can generate two types of characteristic lesions; osteoblastic (osteosclerotic), where bone formation is increased (albeit of low quality bone) and osteolytic, where bone loss and destruction are increased. In the clinical setting, histological examinations often show that metastatic lesions arising from solid tumors are heterogeneous.5 Although maintaining a degree of heterogeneity, prostate cancer metastases have traditionally been observed to form predominantly osteoblastic lesions.6 Despite this, evidence suggests that osteolytic activity is required to precondition bone tissue during the development of prostate cancer bone metastasis.7, 8 One key feature of osteolytic activity in bone metastases is an impaired function of the osteoblasts, caused by tumor-derived factors. Among them, the Wnt signaling inhibitor Dickkopf-1 (DKK-1) is considered to have a major role. Wnt signaling regulates osteoblast differentiation and function and is therefore important for bone homeostasis.9 Therefore, DKK-1 as a Wnt inhibitor negatively regulates osteoblast differentiation.10 Although the role of DKK-1 in cancer remains controversial with claims of both tumor-suppressor and promotor roles depending on the cancer type,11, 12, 13, 14, 15 it has been convincingly exhibited that elevated levels are responsible for KB-R7943 mesylate the induction of osteolytic lesions in bone-seeking cancers such as multiple myeloma and breast cancer.16, 17, 18, 19 Furthermore, we have previously shown that DKK-1 is elevated in the serum of prostate cancer patients and high levels of serum DKK-1 were associated with a poorer prognosis.20 In addition, elevated levels of DKK-1 in prostate bone metastases have also been associated with a poorer survival.21 P38 mitogen-activated protein kinases (MAPKs) are activated by a variety of environmental insults and inflammatory cytokines, controlling numerous cell functions, KB-R7943 mesylate including cell cycle, apoptosis and proliferation. p38 MAPK comprises four unique isoforms (p38by stimulating the differentiation and proliferation of osteoblasts through a Cbfa-1-dependent pathway.38 C4-2B cells promote mixed osteolytic and osteoblastic lesions by the expression of Wnts and BMPs, which directly promote osteoblastogenesis and indirectly promote osteoclastogenesis.35, 39 Similarly, DU145 cells also promote the formation of mixed lesions This highlights a key role of the levels of the Wnt inhibitor DKK-1 in regulating the osteoblastic/osteolytic appearance of prostate cancer bone metastases. We show here that this activation of p38 MAPK signaling using anisomycin also mediates an increased DKK-1 expression in prostate cancer cell lines, which normally have low levels of DKK-1. Although the increases in DKK-1 mRNA expression are not to the same level of those observed in the untreated PC3 cells, they are indicative of a role of p38 signaling in defining the osteotropic signature of prostate cancer cells. When used to target p38 MAPK in solid malignancies, the small molecule inhibitors, LY2228820 and SB202190, had promising antitumor effects in preclinical studies,48, 49 and their therapeutic potential is being currently investigated in clinical trials (“type”:”clinical-trial”,”attrs”:”text”:”NCT01393990″,”term_id”:”NCT01393990″NCT01393990, “type”:”clinical-trial”,”attrs”:”text”:”NCT01663857″,”term_id”:”NCT01663857″NCT01663857). Small molecule KB-R7943 mesylate inhibitors of p38 MAPK display varying potencies of inhibition with regard to the individual MAPK isoforms (according to the supplier). Although our results show that three such inhibitors had suppressive effects on DKK-1 expression, some more potent than others, it is difficult to differentiate further the role of the individual isoforms. To elucidate further the association between DKK-1 and individual p38 MAPK isoforms, PC3.