In silico studying of the whole protein structure and dynamics of Dickkopf family members showed that N-terminal domain of Dickkopf 2 in contrary to other Dickkopfs facilitates its interaction with low density lipoprotein receptor related protein 5/6.

Wnt (Wingless Int) signaling pathway has been known to be dysregulated in several human cancers, especially colorectal cancer (CRC). The Dickkopf (DKK) family which consists of four secreted proteins in vertebrates (DKK 1, 2, 3, 4) is one of the most critical antagonist families for Wnt signaling pathway. They typically antagonize Wnt/ß-catenin signaling by binding and inhibiting Wnt co-receptors, LRP5/6 (low density lipoprotein receptor related protein 5/6). However, except for DKK1 (Dickkopf 1), details about structure and function of the members of this family are poorly defined. In this study, main Dickkopf family members were analyzed structurally, using protein structure prediction tools, molecular dynamics (MD), molecular docking and energy analyses. Three dimensional structure of whole DKKs was predicted and their interaction with LRP6 was investigated in detail. The results indicated that in DKK family members, a considerable diversity, in the case of structure, activity and physicochemical properties was seen. This diversity was more profound in DKK3 (Dickkopf3). Interestingly, the interaction mode of DKK2 (Dickkopf2) with its receptor, LRP6, was shown to be substantially different from other Dickkopf family members while N-terminal region of this ligand was also involved in the binding to the LRP6-P3P4. Moreover, the cysteine-rich domain 2 (CRD2) of DKK1 and DKK3 had a higher binding affinity to LRP6 in comparison with the whole protein structures. Communicated by Ramaswamy H. Sarma.

Expression of DKK1 in gallus of distraction gap during mandibular distraction osteogenesis and its implication / 中华医学美学美容杂志

Objective To investigate the expression of Wnt/β-catenin signal antagonist DKK1 protein in callus of distraction gap during mandibular distraction osteogenesis (MDO).Methods Twenty four healthy New Zealand rabbits were randomly divided into distraction group,fracture control group,with twelve rabbits each,respectively.In distraction group,bilateral mandibular distraction models were established.In control group,after bilateral mandibular osteotomy,the two bone fragments were fixed by titanium plate and screws with a 5 mm gap.The expression of DKK1 in the distracted calluses was analyzed by cell digital imaging software.Results Expression of DKK1 was colocalized in the nucleus and cytoplasm of osteoblasts,fibroblasts,cartilageand newly embedded osteocytes.The expression of DKK1 increased following distraction activated after surgery,peaked at 10 days after surgery,the population of cells that stained for DKK1 decreased gradually.At 31 to 38 days postoperatively,DKK1 expression reduced gradually,mainly located in the osteocyte,and both nucleus and cytoplasm were positive staining.At each time point,the expression of DKK1 in distraction group was higher than that in the control group and the difference was statistically significant (P＜0.05).Conclusions During MDO,the Wnt/β-catenin pathway is activated due to the distraction and mechanical strain on the bone.With the increased expression of Wnt-related factors,the endogenous negative feedback is enhanced to induce DKK1 expression and to regulate the activated Wnt/β-catenin pathway.This would be beneficial to the new bone formation and remodeling in the distraction gap.

The relationship between DKK1 protein expression and lymph node invasion, and prognosis in patients with intrahepatic cholangiocarcinoma / 实用肿瘤学杂志

Objective The objectives of this study were to investigate the relationship between DKK1 protein expression and lymph node invasion,and prognosis in patients with intrahepatic cholangiocarcinoma.Methods From January 2005 to December 2012,78 patients with intrahepatic cholangiocarcinoma were treated with endoscopic resection.Tissue microarray of intrahepatic cholangiocarcinoma and adjacent tissues were done and biochemical indexes were measured before operation.The patients were recruited every 3 months after operation.The Kaplan-Meier method was used to analyze the recurrence-free survival curve and the overall survival curve.The Cox proportional hazards regression model was used to analyze the multivariate analysis and to determine the factors that affect the disease-free survival(RFS)and overall survival(OS).Results There were significant differences in the expression of GGT,hepatic portal lymph node invasion,Child-Pugh grade,MMP9 and DKK1 protein in the negative and positive expression of intrahepatic cholangiocarcinoma(P ＜ 0.05).The positive expression rate of DKK1 protein in intrahepatic cholangiocarcinoma was 35.90％ (28/78),and the positive expression rate of DKK1 protein in hilar cholangiocarcinoma was 14.10％ (11/78).RFS and OS in 78 cases of intrahepatic cholangiocarcinoma were 51.28％ (40/78) and 50.00％ (38/78),41.03 ％ (32/78) and 38.46％ (30/ 78),25.64％ (20/78) and 23.08％ (18/78) after surgery for 1,3 and 5 years,respectively.The results from univariate and multivariate analysis showed that GGT,CA19-9,CEA,tumor size,DKK1 and hilar lymph node invasion were the prognostic factors of OS in patients with intrahepatic cholangiocarcinoma.CEA,tumor size,DKK1 and hilar lymph node involvement were prognostic factors for RFS in patients with intrahepatic cholangiocarcinoma.DKK1 protein expression positive and negative OS curve or RFS curve showed that 5 years after intrahepatic cholangiocarcinoma patients DKK1 protein expression positive and negative OS were 28.20％ and 20.51％;RFS were 24.36％ and 21.79％.Conclusion The expression of DKK1 protein is closely related to lymph node invasion in patients with intrahepatic cholangiocarcinoma.The expression of DKK1 protein is the prognostic factor of OS and RFS in patients with intrahepatic cholangiocarcinoma.

Serum expression of DKK1 protein in patients with non-small cell lung cancer and its relationship with osseous metastasis / 肿瘤研究与临床

Objective To explore the serum expression of DKK1 protein, a Wnt signaling pathway inhibitor in patients with non-small cell lung cancer (NSCLC) and its relationship with osseous metastasis. Methods Serum DKK1 protein levels were assayed by enzyme-linked immunosorbent assay (ELISA) in NSCLC patients, including 33 NSCLC patients with osseous metastasis and 41 NSCLC patients without respectively, and 32 healthy volunteers were served as the control group. Furthermore, the differential expression of the serum DKK1 protein level between the patients and the volunteers was compared by using the variance analysis and the independent sample t test. The correlation between DKK1 expression and bone metastasis was detected by Pearson correlation analysis. Results Serum DKK1 protein level of NSCLC patients was (79.6±8.3) ng/ml, which was significantly higher than that in healthy volunteers [(21.5±6.4) ng/ml, t=13.17, P=0.001]. The serum DKK1 level in osseous metastasis group was (110.3±11.4) ng/ml, which was significantly higher than that in non-skeletal metastasis group [(60.7±10.5) ng/ml, t=14.128, P=0.003]. The positive association was observed between the DKK1 level in the peripheral blood and osseous metastasis in NSCLC patients (r=0.855, P<0.001). Conclusion The serum expression level of DKK1 protein in NSCLC patients is closely related to the osseous metastasis, which may be a predicting biomarker for the osseous metastasis.

Opposing Roles of Wnt Inhibitors IGFBP-4 and Dkk1 in Cardiac Ischemia by Differential Targeting of LRP5/6 and ß-catenin.

BACKGROUND: Myocardial infarction is one of the leading causes of morbidity and mortality worldwide, triggering irreversible myocardial cell damage and heart failure. The role of low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) as coreceptors of the Wnt/ß-catenin pathway in the adult heart remain unknown. Insulin-like growth factor binding protein 4 and dickkopf-related protein 1 (Dkk1) are 2 secreted LRP5/6 binding proteins that play a crucial role in heart development through preventing Wnt/ß-catenin pathway activation. However, their roles in the adult heart remain unexplored. METHODS: To understand the role of LRP5/6 and ß-catenin in the adult heart, we constructed conditional cardiomyocyte-specific LRP5/6 and ß-catenin knockout mice and induced surgical myocardial infarction. We also directly injected recombinant proteins of insulin-like growth factor binding protein 4 and Dkk1 into the heart immediately following myocardial infarction to further examine the mechanisms through which these proteins regulate LRP5/6 and ß-catenin. RESULTS: Deletion of LRP5/6 promoted cardiac ischemic insults. Conversely, deficiency of ß-catenin, a downstream target of LRP5/6, was beneficial in ischemic injury. It is interesting to note that although both insulin-like growth factor binding protein 4 and Dkk1 are secreted Wnt/ß-catenin pathway inhibitors, insulin-like growth factor binding protein 4 protected the ischemic heart by inhibiting ß-catenin, whereas Dkk1 enhanced the injury response mainly through inducing LRP5/6 endocytosis and degradation. CONCLUSIONS: Our findings reveal previously unidentified dual roles of LRP5/6 involved in the cardiomyocyte response to ischemic injury. These findings suggest new therapeutic strategies in ischemic heart disease by fine-tuning LRP5/6 and ß-catenin signaling within the Wnt/ß-catenin pathway.