su-6656 and Prostatic-Neoplasms

N-myc downstream regulated gene-1 (NDRG1) is a potent metastasis suppressor that plays a key role in regulating signaling pathways involved in mediating cancer cell invasion and migration, including those derived from prostate, colon, etc. However, the mechanisms and molecular targets through which NDRG1 reduces cancer cell invasion and migration, leading to inhibition of cancer metastasis, are not fully elucidated. In this investigation, using NDRG1 over-expression models in three tumor cell-types (namely, DU145, PC3MM and HT29) and also NDRG1 silencing in DU145 and HT29 cells, we reveal that NDRG1 decreases phosphorylation of a key proto-oncogene, cellular Src (c-Src), at a well-characterized activating site (Tyr416). NDRG1-mediated down-regulation of EGFR expression and activation were responsible for the decreased phosphorylation of c-Src (Tyr416). Indeed, NDRG1 prevented recruitment of c-Src to EGFR and c-Src activation. Moreover, NDRG1 suppressed Rac1 activity by modulating phosphorylation of a c-Src downstream effector, p130Cas, and its association with CrkII, which acts as a "molecular switch" to activate Rac1. NDRG1 also affected another signaling molecule involved in modulating Rac1 signaling, c-Abl, which then inhibited CrkII phosphorylation. Silencing NDRG1 increased cell migration relative to the control and inhibition of c-Src signaling using siRNA, or a pharmacological inhibitor (SU6656), prevented this increase. Hence, the role of NDRG1 in decreasing cell migration is, in part, due to its inhibition of c-Src activation. In addition, novel pharmacological agents, which induce NDRG1 expression and are currently under development as anti-metastatic agents, markedly increase NDRG1 and decrease c-Src activation. This study leads to important insights into the mechanism involved in inhibiting metastasis by NDRG1 and how to target these pathways with novel therapeutics.

Topics: Adenocarcinoma; Cell Cycle Proteins; Cell Line, Tumor; Cell Movement; Colonic Neoplasms; Crk-Associated Substrate Protein; Down-Regulation; Enzyme Activation; ErbB Receptors; Gene Expression Regulation, Neoplastic; Genes, src; Humans; Indoles; Intracellular Signaling Peptides and Proteins; Male; Neoplasm Proteins; p21-Activated Kinases; Phosphorylation; Prostatic Neoplasms; Protein Processing, Post-Translational; Proto-Oncogene Mas; Proto-Oncogene Proteins c-abl; Proto-Oncogene Proteins c-crk; Proto-Oncogene Proteins pp60(c-src); rac1 GTP-Binding Protein; Recombinant Proteins; RNA Interference; RNA, Small Interfering; Signal Transduction; Sulfonamides

The androgen receptor (AR) is essential for the growth of prostate cancer cells. Here, we report that tyrosine phosphorylation of AR is induced by growth factors and elevated in hormone-refractory prostate tumors. Mutation of the major tyrosine phosphorylation site in AR significantly inhibits the growth of prostate cancer cells under androgen-depleted conditions. The Src tyrosine kinase appears to be responsible for phosphorylating AR, and there is a positive correlation of AR tyrosine phosphorylation with Src tyrosine kinase activity in human prostate tumors. Our data collectively suggest that growth factors and their downstream tyrosine kinases, which are elevated during hormone-ablation therapy, can induce tyrosine phosphorylation of AR and such modification may be important for prostate tumor growth under androgen-depleted conditions.

Topics: Androgens; Animals; Cell Line, Tumor; Chlorocebus aethiops; COS Cells; Dihydrotestosterone; Epidermal Growth Factor; Gene Expression Regulation, Neoplastic; Humans; Immunohistochemistry; Indoles; Interleukin-6; Kinetics; Male; Mice; Mice, SCID; Neuregulin-1; Phosphorylation; Prostatic Neoplasms; Pyrimidines; Receptors, Androgen; src-Family Kinases; Sulfonamides; Tyrosine; Xenograft Model Antitumor Assays