Hot off the presses! Jun 14 Cancer Cell

The Jun 14 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:

• Oncogene-Induced Mitotic Stress: p53 and pRb Get Mad Too
  - Cancer Cell 19(6):691-692 (2011)
  Oncogenic signaling frequently results in unscheduled overexpression of cell cycle proteins and replicative stress. In this issue of Cancer Cell, Schvartzman et al. show that inactivation of p53 or pRb induces Mad2, and the overexpression of this mitotic checkpoint protein is a necessary event during oncogene-induced mitotic stress.
• A Lipid Kinase Cousin Cooperates to Promote Cancer
  - Cancer Cell 19(6):693-695 (2011)
  Phosphoinositide 3-kinases (PI3Ks) are considered promising drug targets in oncology. In this issue of Cancer Cell, Schmid et al. demonstrate that the PI3Kγ isoform is required for inflammatory myeloid cells to traffic to tumors. Though tumor cells do not express PI3Kγ, selective inhibition of this isoform suppresses tumor growth and angiogenesis.
• ROCK-Driven Actomyosin Contractility Induces Tissue Stiffness and Tumor Growth
  - Cancer Cell 19(6):695-697 (2011)
  The tumor environment consists of tumor-associated cells, such as macrophages, fibroblasts, and extracellular matrix, and has an important impact on tumor progression. In this issue of Cancer Cell, Samuel et al. show that ROCK-driven actomyosin contractility increases tissue stiffness affecting epidermal homeostasis, as well as tumor growth and progression.
• Turning Reciprocal Feedback Regulation into Combination Therapy
  - Cancer Cell 19(6):697-699 (2011)
  Two recent Cancer Cell articles report the discovery of reciprocal feedback regulation between androgenic and PTEN loss/PI3K-AKT signaling in prostate cancer. Both studies link endocrine regulation with a common oncogenic pathway, which led to the development of a combination therapeutic approach with immediate application in prostate cancer.
• Mad2 Is a Critical Mediator of the Chromosome Instability Observed upon Rb and p53 Pathway Inhibition
  - Cancer Cell 19(6):701-714 (2011)
  Multiple mechanisms have been proposed to explain how Rb and p53 tumor suppressor loss lead to chromosome instability (CIN). It was recently shown that Rb pathway inhibition causes overexpression of the mitotic checkpoint gene Mad2, but whether Mad2 overexpression is required to generate CIN in this context is unknown. Here, we show that CIN in cultured cells lacking Rb family proteins requires Mad2 upregulation and that this upregulation is also necessary for CIN and tumor progression in vivo. Mad2 is also repressed by p53 and its upregulation is required for CIN in a p53 mutant tumor model. These results demonstrate that Mad2 overexpression is a critical mediator of the CIN observed upon inactivation of two major tumor suppressor pathways.
• Receptor Tyrosine Kinases and TLR/IL1Rs Unexpectedly Activate Myeloid Cell PI3Kγ, A Single Convergent Point Promoting Tumor Inflammation and Progression
  - Cancer Cell 19(6):715-727 (2011)
  Tumor inflammation promotes angiogenesis, immunosuppression, and tumor growth, but the mechanisms controlling inflammatory cell recruitment to tumors are not well understood. We found that a range of chemoattractants activating G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and Toll-like/IL-1 receptors (TLR/IL1Rs) unexpectedly initiate tumor inflammation by activating the PI3-kinase isoform p110γ in Gr1+CD11b+ myeloid cells. Whereas GPCRs activate p110γ in a Ras/p101-dependent manner, RTKs and TLR/IL1Rs directly activate p110γ in a Ras/p87-dependent manner. Once activated, p110γ promotes inside-out activation of a single integrin, α4β1, causing myeloid cell invasion into tumors. Pharmacological or genetic blockade of p110γ suppressed inflammation, growth, and metastasis of implanted and spontaneous tumors, revealing an important therapeutic target in oncology.
• Pancreatitis-Induced Inflammation Contributes to Pancreatic Cancer by Inhibiting Oncogene-Induced Senescence
  - Cancer Cell 19(6):728-739 (2011)
  Pancreatic acinar cells of adult mice (≥P60) are resistant to transformation by some of the most robust oncogenic insults including expression of K-Ras oncogenes and loss of p16Ink4a/p19Arf or Trp53 tumor suppressors. Yet, these acinar cells yield pancreatic intraepithelial neoplasias (mPanIN) and ductal adenocarcinomas (mPDAC) if exposed to limited bouts of non-acute pancreatitis, providing they harbor K-Ras oncogenes. Pancreatitis contributes to tumor progression by abrogating the senescence barrier characteristic of low-grade mPanINs. Attenuation of pancreatitis-induced inflammation also accelerates tissue repair and thwarts mPanIN expansion. Patients with chronic pancreatitis display senescent PanINs, providing they have received antiinflammatory drugs. These results support the concept that antiinflammatory treatment of people diagnosed with pancreatitis may reduce their risk of developing PDAC.
• Loss or Inhibition of Stromal-Derived PlGF Prolongs Survival of Mice with Imatinib-Resistant Bcr-Abl1+ Leukemia
  - Cancer Cell 19(6):740-753 (2011)
  Imatinib has revolutionized the treatment of Bcr-Abl1+ chronic myeloid leukemia (CML), but, in most patients, some leukemia cells persist despite continued therapy, while others become resistant. Here, we report that PlGF levels are elevated in CML and that PlGF produced by bone marrow stromal cells (BMSCs) aggravates disease severity. CML cells foster a soil for their own growth by inducing BMSCs to upregulate PlGF, which not only stimulates BM angiogenesis, but also promotes CML proliferation and metabolism, in part independently of Bcr-Abl1 signaling. Anti-PlGF treatment prolongs survival of imatinib-sensitive and -resistant CML mice and adds to the anti-CML activity of imatinib. These results may warrant further investigation of the therapeutic potential of PlGF inhibition for (imatinib-resistant) CML.
• Cell of Origin of Small Cell Lung Cancer: Inactivation of Trp53 and Rb1 in Distinct Cell Types of Adult Mouse Lung
  - Cancer Cell 19(6):754-764 (2011)
  Small cell lung cancer (SCLC) is one of the most lethal human malignancies. To investigate the cellular origin(s) of this cancer, we assessed the effect of Trp53 and Rb1 inactivation in distinct cell types in the adult lung using adenoviral vectors that target Cre recombinase to Clara, neuroendocrine (NE), and alveolar type 2 (SPC-expressing) cells. Using these cell type-restricted Adeno-Cre viruses, we show that loss of Trp53 and Rb1 can efficiently transform NE and SPC-expressing cells leading to SCLC, albeit SPC-expressing cells at a lesser efficiency. In contrast, Clara cells were largely resistant to transformation. The results indicate that although NE cells serve as the predominant cell of origin of SCLC a subset of SPC-expressing cells are also endowed with this ability.
• Impairment of Cytoplasmic eIF6 Activity Restricts Lymphomagenesis and Tumor Progression without Affecting Normal Growth
  - Cancer Cell 19(6):765-775 (2011)
  Eukaryotic Initiation Factor 6 (eIF6) controls translation by regulating 80S subunit formation. eIF6 is overexpressed in tumors. Here, we demonstrate that eIF6 inactivation delays tumorigenesis and reduces tumor growth in vivo. eIF6+/− mice resist to Myc-induced lymphomagenesis and have prolonged tumor-free survival and reduced tumor growth. eIF6+/− mice are also protected by p53 loss. Myc-driven lymphomas contain PKCβII and phosphorylated eIF6; eIF6 is phosphorylated by tumor-derived PKCβII, but not by the eIF4F activator mTORC1. Mutation of PKCβII phosphosite of eIF6 reduces tumor growth. Thus, eIF6 is a rate-limiting controller of initiation of translation, able to affect tumorigenesis and tumor growth. Modulation of eIF6 activity, independent from eIF4F complex, may lead to a therapeutical avenue in tumor therapy.
• Actomyosin-Mediated Cellular Tension Drives Increased Tissue Stiffness and β-Catenin Activation to Induce Epidermal Hyperplasia and Tumor Growth
  - Cancer Cell 19(6):776-791 (2011)
  Tumors and associated stroma manifest mechanical properties that promote cancer. Mechanosensation of tissue stiffness activates the Rho/ROCK pathway to increase actomyosin-mediated cellular tension to re-establish force equilibrium. To determine how actomyosin tension affects tissue homeostasis and tumor development, we expressed conditionally active ROCK2 in mouse skin. ROCK activation elevated tissue stiffness via increased collagen. β-catenin, a key element of mechanotranscription pathways, was stabilized by ROCK activation leading to nuclear accumulation, transcriptional activation, and consequent hyperproliferation and skin thickening. Inhibiting actomyosin contractility by blocking LIMK or myosin ATPase attenuated these responses, as did FAK inhibition. Tumor number, growth, and progression were increased by ROCK activation, while ROCK blockade was inhibitory, implicating actomyosin-mediated cellular tension and consequent collagen deposition as significant tumo! r promoters.
• Cell Autonomous Role of PTEN in Regulating Castration-Resistant Prostate Cancer Growth
  - Cancer Cell 19(6):792-804 (2011)
  Alteration of the PTEN/PI3K pathway is associated with late-stage and castrate-resistant prostate cancer (CRPC). However, how PTEN loss is involved in CRPC development is not clear. Here, we show that castration-resistant growth is an intrinsic property of Pten null prostate cancer (CaP) cells, independent of cancer development stage. PTEN loss suppresses androgen-responsive gene expressions by modulating androgen receptor (AR) transcription factor activity. Conditional deletion of Ar in the epithelium promotes the proliferation of Pten null cancer cells, at least in part, by downregulating the androgen-responsive gene Fkbp5 and preventing PHLPP-mediated AKT inhibition. Our findings identify PI3K and AR pathway crosstalk as a mechanism of CRPC development, with potentially important implications for CaP etiology and therapy.
• PI3Kγ Mediates Kaposi's Sarcoma-Associated Herpesvirus vGPCR-Induced Sarcomagenesis
  - Cancer Cell 19(6):805-813 (2011)
  Angioproliferative tumors induced by the Kaposi's sarcoma-associated herpesvirus (KSHV) have been successfully treated with rapamycin, which provided direct evidence of the clinical activity of mTOR inhibitors in human malignancies. However, prolonged mTOR inhibition may raise concerns in immunocompromised patients, including AIDS-Kaposi's sarcoma (KS). Here, we explored whether KSHV oncogenes deploy cell type-specific signaling pathways activating mTOR, which could be exploited to halt KS development while minimizing immune suppressive effects. We found that PI3Kγ, a PI3K isoform exhibiting restricted tissue distribution, is strictly required for signaling from the KSHV-encoded vGPCR oncogene to Akt/mTOR. Indeed, by using an endothelial-specific gene delivery system modeling KS development, we provide genetic and pharmacological evidence that PI3Kγ may represent a suitable molecular target for therapeutic intervention in KS.
• CCL18 from Tumor-Associated Macrophages Promotes Breast Cancer Metastasis via PITPNM3
  - Cancer Cell 19(6):814-816 (2011)