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Increasing evidence suggests that chromosomal regions containing microRNAs are functionally important in cancers. Here, we show that genomic loci encoding miR-204 are frequently lost in multiple cancers, including ovarian cancers, pediatric renal tumors, and breast cancers. MiR-204 shows drastically reduced expression in several cancers and acts as a potent tumor suppressor, inhibiting tumor metastasis in vivo when systemically delivered. We demonstrated that miR-204 exerts its function by targeting genes involved in tumorigenesis including brain-derived neurotrophic factor (BDNF), a neurotrophin family member which is known to promote tumor angiogenesis and invasiveness. Analysis of primary tumors shows that increased expression of BDNF or its receptor tropomyosin-related kinase B (TrkB) parallel a markedly reduced expression of miR-204. Our results reveal that loss of miR-204 results in BDNF overexpression and subsequent activation of the small GTPase Rac1 and actin reorganization through the AKT/mTOR signaling pathway leading to cancer cell migration and invasion. These results suggest that microdeletion of genomic loci containing miR-204 is directly linked with the deregulation of key oncogenic pathways that provide crucial stimulus for tumor growth and metastasis. Our findings provide a strong rationale for manipulating miR-204 levels therapeutically to suppress tumor metastasis.

The aberrant overexpression of Wilms tumor 1 (WT1) in myeloid leukemia plays an important role in blast cell survival and resistance to chemotherapy. High expression of WT1 is also associated with relapse and shortened disease-free survival in patients. However, the mechanisms by which WT1 expression is regulated in leukemia remain unclear. Here, we report that heat shock protein 90 (Hsp90), which plays a critical role in the folding and maturation of several oncogenic proteins, associates with WT1 protein and stabilizes its expres- IntroductionThe Wilms tumor 1 (WT1) gene encodes a zinc finger transcription factor that is important for normal urogenital development and cancer pathogenesis. [1][2][3] Overexpression of WT1 has been observed in a wide range of solid tumors and hematopoietic malignancies, including acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) in blastic phase, as well as in myelodysplastic syndromes (MDSs). [4][5][6] Several studies have suggested that WT1 expression plays an important role in myelopoiesis, cell proliferation, and differentiation arrest. 7,8 In addition, overexpression of WT1 has been proposed to sustain survival of leukemia blast cells. 9 Coexpression of WT1 and the fusion protein AML1-ETO in transgenic mice rapidly induces AML, further emphasizing the proto-oncogenic function of WT1. 8 Furthermore, high levels of WT1 expression in acute leukemias have been associated with lower complete remission rates and reduced overall and disease-free survival. 10,11 WT1 has also shown to be a repressor or activator for several important genes, such as the antiapoptotic gene Bcl-2 and the oncogene c-Myc. 12 This overexpression of WT1 not only makes it an attractive prognostic marker for minimal residual disease but also a promising target for immunotherapy. 13,14 However, despite these findings, little is known about the molecular mechanisms of WT1 regulation in leukemia.Heat shock protein 90 (Hsp90) is an important molecular chaperone that plays a key role in the conformational maturation and stabilization of signaling proteins involved in cell growth and survival. 15,16 Hsp90 is considered a promising therapeutic target, as its inhibition simultaneously affects the activity of multiple oncogenic proteins. 17 The first-generation Hsp90 inhibitor 17-AAG [17-(allylamino)-17-demethoxygeldanamycin], which preferentially binds to the active form of Hsp90 in tumor cells, 18 has shown promising antitumor activity in preclinical models and is currently in clinical trials. 19,20 More potent second-generation Hsp90 inhibitors that are structurally unrelated to 17-AAG, such as STA-9090, a novel resorcinolcontaining compound, 21 are also in clinical development. Hsp90 also cooperates with the chaperone protein Hsp70 to properly fold its protein substrates, and this functional cooperation is mediated by additional cochaperones. 22 Although Hsp70 has been shown to chaperone WT1 and plays a crucial role in its proper functioning during normal kidney development, 23 the role of Hsp90 in ...

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Background: Tumor necrosis factor ␣-related apoptosis-inducing ligand (TRAIL) resistance in leukemia is not fully understood. Results: shRNA-targeted knockdown of WT1 oncogene sensitizes TRAIL-resistant leukemia cells to TRAIL-induced cell death. Conclusion: WT1 expression mediates TRAIL resistance in leukemia cells by inducing antiapoptotic protein Bcl-xL. Significance: Approaches to silence WT1 expression can be exploited to overcome TRAIL resistance in myeloid leukemias.Tumor necrosis factor ␣-related apoptosis-inducing ligand (TRAIL) is considered a promising cancer therapeutic agent due to its ability to induce apoptosis in a variety of cancer cells, while sparing normal cells. However, many human tumors including acute myeloid leukemia (AML) are partially or completely resistant to monotherapy with TRAIL, limiting its therapeutic utility. Therefore, identification of factors that contribute to TRAIL resistance may facilitate future development of more effective TRAIL-based cancer therapies. Here, we report a previously unknown role for WT1 in mediating TRAIL resistance in leukemia. Knockdown of WT1 with shRNA rendered TRAILresistant myeloid leukemia cells sensitive to TRAIL-induced cell death, and re-expression of shRNA-resistant WT1 restored TRAIL resistance. Notably, TRAIL-mediated apoptosis in WT1-silenced cells was largely due to down-regulation of the antiapoptotic protein Bcl-xL. Moreover, WT1 expression strongly correlated with overexpression of Bcl-xL in AML cell lines and blasts from AML patients. Furthermore, we found that WT1 transactivates Bcl-xL by directly binding to its promoter. We previously showed that WT1 is a novel client protein of heat shock protein 90 (Hsp90). Consistent with this, pharmacological inhibition of Hsp90 resulted in reduced WT1 and Bcl-xL expression leading to increased sensitivity of leukemia cells to TRAIL-mediated apoptosis. Collectively, our results suggest that WT1-dependent Bcl-xL overexpression contributes to TRAIL resistance in myeloid leukemias.Chemotherapy has improved the outcome for leukemia patients, but it often results in highly debilitating side effects due to considerable toxicity toward normal tissues. TRAIL 2 is a promising cancer therapy that preferentially induces apoptosis in cancer cells without exhibiting adverse effects on normal cells (1, 2). TRAIL induces apoptosis through binding its two proapoptotic receptors, DR4 (TRAIL-R1) and DR5 (TRAIL-R2), followed by recruitment of an adaptor molecule (Fas-associated death domain) and initiator caspases (caspase-8/10) to the death-inducing signaling complex and subsequent activation of downstream effector caspases (3). The apoptotic signals at the death receptors can cross-talk with the mitochondrial pathway through the caspase-8 cleavage of Bid. The truncated Bid translocates to mitochondria, triggers cytochrome c release, and amplifies the apoptotic signal (4). Overexpression of the antiapoptotic molecules such as Bcl-2 and Bcl-xL can block cytochrome c release and subsequent caspase activation in res...