Hot off the presses! May 05 Cancer Cell

The May 05 issue of the Cancer Cell is now up on Pubget (About Cancer Cell): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• PI3K Inhibition Overcomes Trastuzumab Resistance: Blockade of ErbB2/ErbB3 Is Not Always Enough
  - Cancer Cell 15(5):353-355 (2009)
  Trastuzumab targets ErbB2 and is used for treating ErbB2-overexpressing breast cancers. In this issue of Cancer Cell, Junttila et al. show that trastuzumab disrupts ligand-independent ErbB2/ErbB3/PI3K complexes and blocks AKT signaling; if PI3K is mutated, complex disruption does not inhibit AKT, which explains why trastuzumab is ineffective in some tumors.
• Inflamed Snail Speeds Metastasis
  - Cancer Cell 15(5):355-357 (2009)
  Macrophage infiltration and inflammatory cytokines are powerful drivers of tumorigenesis and metastasis. Wu et al., in this issue of Cancer Cell, show that TNFα-dependent NFκB activation induces COP9 signalosome-mediated inhibition of GSK3β and the SCFβ-TRCP ubiquitin ligase, thus leading to stabilization of the transcription factor Snail and promoting cell migration and metastasis.
• YB-1 Translational Control of Epithelial-Mesenchyme Transition
  - Cancer Cell 15(5):357-359 (2009)
  Transitions between epithelial and mesenchmal phenotypes play critical roles in normal development and cancer progression. In this issue of Cancer Cell, Evdokimova et al. demonstrate that YB-1 regulates epithelial-mesenchyme transition (EMT) by inducing cap-independent translation of mRNAs encoding EMT-promoting factors and suppressing cap-dependent translation of mRNAs encoding growth-promoting factors.
• Agonizing Integrin Antagonists?
  - Cancer Cell 15(5):359-361 (2009)
  A recent study published in Nature Medicine reports that low-dose treatment with RGD-mimetic integrin inhibitors may paradoxically enhance angiogenesis and tumor growth. This work implies that delivery of these agents should be redesigned in order to avoid nanomolar plasma concentrations and to improve their efficacy to treat human cancers.
• Regulation of XIAP Translation and Induction by MDM2 following Irradiation
  - Cancer Cell 15(5):363-375 (2009)
  Increases in protein levels of XIAP in cancer cells have been associated with resistance to apoptosis induced by cellular stress. Herein we demonstrate that the upregulation of XIAP protein levels is regulated by MDM2 at the translational level. MDM2 was found to physically interact with the IRES of the XIAP 5′-UTR, and to positively regulate XIAP IRES activity. This XIAP IRES-dependent translation was significantly increased in MDM2-transfected cells where MDM2 accumulated in the cytoplasm. Cellular stress and DNA damage triggered by irradiation induced the dephosphorylation and cytoplasmic localization of MDM2, which also led to an increase in IRES-dependent XIAP translation. Upregulation of XIAP in MDM2-overexpressing cancer cells in response to irradiation resulted in resistance of these cells to radiation-induced apoptosis.
• PRIMA-1 Reactivates Mutant p53 by Covalent Binding to the Core Domain
  - Cancer Cell 15(5):376-388 (2009)
  Restoration of wild-type p53 expression triggers cell death and eliminates tumors in vivo. The identification of mutant p53-reactivating small molecules such as PRIMA-1 opens possibilities for the development of more efficient anticancer drugs. Although the biological effects of PRIMA-1 are well demonstrated, little is known about its molecular mechanism of action. We show here that PRIMA-1 is converted to compounds that form adducts with thiols in mutant p53. Covalent modification of mutant p53 per se is sufficient to induce apoptosis in tumor cells. These findings might facilitate the design of more potent and specific mutant p53-targeting anticancer drugs.
• CDK Inhibitor p18INK4c Is a Downstream Target of GATA3 and Restrains Mammary Luminal Progenitor Cell Proliferation and Tumorigenesis
  - Cancer Cell 15(5):389-401 (2009)
  Mammary epithelia are composed of luminal and myoepithelial/basal cells whose neoplastic transformations lead to distinct types of breast cancers with diverse clinical features. We report that mice deficient for the CDK4/6 inhibitor p18Ink4c spontaneously develop ER-positive luminal tumors at a high penetrance. Ink4c deletion stimulates luminal progenitor cell proliferation at pubertal age and maintains an expanded luminal progenitor cell population throughout life. We demonstrate that GATA3 binds to and represses INK4C transcription. In human breast cancers, low INK4C and high GATA3 expressions are simultaneously observed in luminal A type tumors and predict a favorable patient outcome. Hence, p18INK4C is a downstream target of GATA3, constrains luminal progenitor cell expansion, and suppresses luminal tumorigenesis in the mammary gland.
• Translational Activation of Snail1 and Other Developmentally Regulated Transcription Factors by YB-1 Promotes an Epithelial-Mesenchymal Transition
  - Cancer Cell 15(5):402-415 (2009)
  Increased expression of the transcription/translation regulatory protein Y-box binding protein-1 (YB-1) is associated with cancer aggressiveness, particularly in breast carcinoma. Here we establish that YB-1 levels are elevated in invasive breast cancer cells and correlate with reduced expression of E-cadherin and poor patient survival. Enforced expression of YB-1 in noninvasive breast epithelial cells induced an epithelial-mesenchymal transition (EMT) accompanied by enhanced metastatic potential and reduced proliferation rates. YB-1 directly activates cap-independent translation of messenger RNAs encoding Snail1 and other transcription factors implicated in downregulation of epithelial and growth-related genes and activation of mesenchymal genes. Hence, translational regulation by YB-1 is a restriction point enabling coordinated expression of a network of EMT-inducing transcription factors, likely acting together to promote metastatic spread.
• Stabilization of Snail by NF-κB Is Required for Inflammation-Induced Cell Migration and Invasion
  - Cancer Cell 15(5):416-428 (2009)
  The increased motility and invasiveness of tumor cells are reminiscent of epithelial-mesenchymal transition (EMT), which occurs during embryonic development, wound healing, and metastasis. In this study, we found that Snail is stabilized by the inflammatory cytokine TNFα through the activation of the NF-κB pathway. We demonstrated that NF-κB is required for the induction of COP9 signalosome 2 (CSN2), which, in turn, blocks the ubiquitination and degradation of Snail. Furthermore, we showed that the expression of Snail correlated with the activation of NF-κB in cancer cell lines and metastatic tumor samples. Knockdown of Snail expression inhibited cell migration and invasion induced by inflammatory cytokines and suppressed inflammation-mediated breast cancer metastasis. Our study provides a plausible mechanism for inflammation-induced metastasis.
• Ligand-Independent HER2/HER3/PI3K Complex Is Disrupted by Trastuzumab and Is Effectively Inhibited by the PI3K Inhibitor GDC-0941
  - Cancer Cell 15(5):429-440 (2009)
  Herceptin (trastuzumab) is the backbone of HER2-directed breast cancer therapy and benefits patients in both the adjuvant and metastatic settings. Here, we describe a mechanism of action for trastuzumab whereby antibody treatment disrupts ligand-independent HER2/HER3 interactions in HER2-amplified cells. The kinetics of dissociation parallels HER3 dephosphorylation and uncoupling from PI3K activity, leading to downregulation of proximal and distal AKT signaling, and correlates with the antiproliferative effects of trastuzumab. A selective and potent PI3K inhibitor, GDC-0941, is highly efficacious both in combination with trastuzumab and in the treatment of trastuzumab-resistant cells and tumors.
• Ablation of Key Oncogenic Pathways by RITA-Reactivated p53 Is Required for Efficient Apoptosis
  - Cancer Cell 15(5):441-453 (2009)
  Targeting "oncogene addiction" is a promising strategy for anticancer therapy. We report a potent inhibition of crucial oncogenes by p53 upon reactivation by small-molecule RITA in vitro and in vivo. RITA-activated p53 unleashes the transcriptional repression of antiapoptotic proteins Mcl-1, Bcl-2, MAP4, and survivin; blocks the Akt pathway on several levels; and downregulates c-Myc, cyclin E, and β-catenin. p53 ablates c-Myc expression via several mechanisms at the transcriptional and posttranscriptional level. We show that the threshold for p53-mediated transrepression of survival genes is higher than for transactivation of proapoptotic targets. Inhibition of oncogenes by p53 reduces the cell's ability to buffer proapoptotic signals and elicits robust apoptosis. Our study highlights the role of transcriptional repression for p53-mediated tumor suppression.