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Von Willebrand factor (VWF) is a multimeric protein that mediates platelet adhesion at sites of vascular injury, and ADAMTS13 (a disintegrin and metalloprotease with thrombospondin)is a multidomain metalloprotease that limits platelet adhesion by a feedback mechanism in which fluid shear stress induces proteolysis of VWF and prevents disseminated microvascular thrombosis. Cleavage of the Tyr 1605 -Met 1606 scissile bond in the VWF A2 domain depends on a Glu 1660 -Arg 1668 segment in the same domain and on the noncatalytic spacer domain of ADAMTS13, suggesting that extensive enzyme-substrate interactions facilitate substrate recognition. Based on mutagenesis and kinetic analysis, we find that the ADAMTS13 spacer domain binds to an exosite near the C terminus of the VWF A2 domain. Deleting the spacer domain from ADAMTS13 or deleting the exosite from the VWF substrate reduced the rate of cleavage Ϸ20-fold. A cleavage product containing the exosite was a hyperbolic mixed-type inhibitor of ADAMTS13 proteolysis of either VWF multimers or model peptide substrates but only if the ADAMTS13 enzyme contained the spacer domain. The specificity of this unique mechanism depends on tension-induced unfolding of the VWF A2 domain, which exposes the scissile bond and exosite for interaction with complementary sites on ADAMTS13.enzyme kinetics ͉ thrombotic thrombocytopenic purpura ͉ fluid shear stress

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Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.

An important clinical challenge in prostate cancer therapy is the inevitable transition from androgen-sensitive to castration-resistant and metastatic prostate cancer. Albeit the androgen receptor (AR) signaling axis has been targeted, the biological mechanism underlying the lethal event of androgen independence remains unclear. New emerging evidences indicate that epithelial-to-mesenchymal transition (EMT) and cancer stem cells (CSCs) play crucial roles during the development of castration-resistance and metastasis of prostate cancer. Notably, EMT may be a dynamic process. Castration can induce EMT that may enhance the stemness of CSCs, which in turn results in castration-resistance and metastasis. Reverse of EMT may attenuate the stemness of CSCs and inhibit castration-resistance and metastasis. These prospective approaches suggest that therapies target EMT and CSCs may cast a new light on the treatment of castration-resistant prostate cancer (CRPC) in the future. Here we review recent progress of EMT and CSCs in CRPC.

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Although symmetrical and asymmetrical divisions of stem cells have been extensively studied in invertebrate and mammalian neural epithelia, their role remains largely unknown in mammalian non-neural epithelial development, regeneration and tumorigenesis. Here, using basal and luminal cell-specific markers and cell lineage tracing transgenic mice, we report that in developing prostatic epithelia, basal and luminal cells exhibit distinct division modes. While basal cells display both symmetric and asymmetric divisions leading to different cell fates, luminal cells only exhibit symmetrical divisions. Examination of cell division modes in prostate-specific Pten-null mice indicates that both luminal and basal cells can be cellular origins for prostate cancer. Furthermore, analysis of Sox2-expressing cells in p63 and Pten-null mice suggests that basal cells contribute to the luminal population and tumorigenesis. These findings provide direct evidence for the existence of a hierarchy of epithelial cell lineages during prostate development, regeneration and tumorigenesis.