BBA - Reviews on Cancer (v.1775, #2)

Chemotherapy-induced resistance by ATP-binding cassette transporter genes by Jean-Pierre Gillet; Thomas Efferth; José Remacle (237-262).
A key issue in the treatment of many cancers is the development of resistance to chemotherapeutic drugs. Resistance mechanisms are numerous and complex. One of them is mediated by the overexpression of ATP-binding cassette (ABC) transporters able to efflux drugs out of the tumor cell. The last two decades have seen notable growth of knowledge concerning the involvement of ABC transporters in resistance to chemotherapy. This review emphasizes these transporters, their clinical relevance and the diagnostic methods and strategies to circumvent multidrug resistance (MDR) mediated by ABC transporters.
Keywords: ABC transporter genes; Multidrug resistance;

Roles of cortactin in tumor pathogenesis by László Buday; Julian Downward (263-273).
Cortactin is a ubiquitous actin-binding protein that was originally identified as a substrate for the protein kinase Src. It is accumulated in peripheral, actin-enriched structures of cells, including lamellipodia and membrane ruffles, suggesting that cortactin facilitates actin network formation. In addition, recent data suggests that it regulates various aspects of cell dynamics, including integrin signaling, vesicular transport, axon guidance, and cell migration. A large body of evidence indicates that cortactin is also implicated in the pathogenesis of human neoplasia. It is over-expressed in a number of epithelial carcinomas, including breast cancer and head and neck cancer. Over-expression of cortactin in human tumors has been proposed to result in increased cell migration and metastatic potential. This review aims to focus on cortactin-mediated signaling pathways, with emphasis on its contribution to tumor progression and metastasis formation.
Keywords: Cortactin; Tumor; Cell migration; Podosome; Invadopodium; Metastasis;

Classifying microRNAs in cancer: The good, the bad and the ugly by P. Mathijs Voorhoeve; Reuven Agami (274-282).
MicroRNAs (miRNAs) have quite recently emerged as a novel class of gene regulators. Many miRNAs exhibit altered expression levels in cancer, and we are only starting to understand the functional consequences of the loss or gain of particular miRNAs to the cancerous phenotype. miRNAs can be classified with regard to their role in cancer as the Good, the Bad and the Ugly. The “Good”, those miRNAs that are innocent bystanders in the oncogenic transformation process, whose expression profile might even be used for cancer diagnosis or prognosis. The “Bad”, those miRNAs that are causally linked to tumorigenesis and directly modify tumor suppressor- or oncogenic- pathways. And the “Ugly”, those miRNAs whose inappropriate loss or gain destabilizes the cellular identity of a tumor, which indirectly results in enhanced phenotypic variability and progression of the tumor. Hereunder we will discuss the possible ways in which miRNAs can be relevant to cancer biology, and possible experimental strategies for elucidating the mechanisms involved.
Keywords: MicroRNA; MiRNA; Cancer; Tumor suppressor; Oncogene; Canalization;

The molecular events that lead to the cancer-initiating cell involve critical mutations in genes regulating normal cell growth and differentiation. Cancer stem cells, or cancer initiating cells have been described in the context of acute myeloid leukemia, breast, brain, bone, lung, melanoma and prostate. These cells have been shown to be critical in tumor development and should harbor the mutations needed to initiate a tumor. The origin of the cancer stem cells is not clear. They may be derived from stem cell pools, progenitor cells or differentiated cells that undergo trans-differentiation processes. It has been suggested that cell fusion and/or horizontal gene transfer events, which may occur in tissue repair processes, also might play an important role in tumor initiation and progression. Fusion between somatic cells that have undergone a set of specific mutations and normal stem cells might explain the extensive chromosomal derangements seen in early tumors. Centrosome deregulation can be an integrating factor in many of the mechanisms involved in tumor development. The regulation of the balance between cell renewal and cell death is critical in cancer. Increased knowledge of developmental aspects in relation to self-renewal and differentiation, both under normal and deregulated conditions, will probably shed more light on the mechanisms that lead to tumor initiation and progression.
Keywords: Cancer development; Microenvironment; Stem cell; Cancer stem cell;

During tumour growth the surrounding vasculature forms new vessels which penetrate into the stroma and bring oxygen and nutrients to the proliferating cancer cells. The ability to control and reduce this phenomenon may have important therapeutic implications. Angiogenesis is a complex event which requires endothelial cell sprouting, lumen formation, tubulogenesis and is regulated by the coordinated action of different transcription factors. Studies on promoters of endothelial cell-specific genes or gene inactivation experiments reveal the extreme complexity of the system. Many transcription factors are implicated in vascular development and the majority are not endothelial-specific. Their interaction leads to endothelial cell differentiation and acquisition of arterial, venous and lymphatic properties. Two large families of transcription factors, Foxs and Ets, play a major role in these events. They participate in both embryonic and adult angiogenesis. The FoxO subgroup regulates the correct organization of the vascular system, controlling excessive endothelial growth and inducing apoptosis both in embryos and adult mice. Ets factors participate in early endothelial differentiation and angiogenesis. Many members of this family are expressed very early in the developing vasculature and Ets consensus binding domains are present in essentially all endothelial cell-specific gene promoters. In this review we discuss the overall transcriptional regulation of vascular development with a particular focus on some specific members of these two families considered important in the formation and maintenance of the vascular network.
Keywords: Angiogenesis; Vasculogenesis; Cell transcription; Forkhead transcription factors; Ets transcription factors;

Molecular alterations during insulinoma tumorigenesis by Y.M.H. Jonkers; F.C.S. Ramaekers; E.J.M. Speel (313-332).
Insulinomas are the most common functioning endocrine pancreatic tumors (EPTs). They present with clinical symptoms as a consequence of hypoglycemia induced by inappropriate insulin secretion. The etiology of these tumors is poorly understood. Some tumors may harbor MEN1 gene mutations, the susceptibility gene of the multiple endocrine neoplasia type I syndrome, but most cases show wildtype MEN1. Currently, no reliable clinical tests are available to differentiate benign from malignant tumors. Approximately 30% of the tumors are unresectable, and they often show different growth rates, which hampers treatment. Therefore, a better understanding of the molecular processes underlying the development and progression of insulinomas is required to improve diagnosis, prognosis and therapy. Here we summarize the progress that has been made in insulinoma research in the past decade. We describe the clinical detection, classification and treatment of these tumors, and review the multiplicity of molecular and genetic studies that investigated tumor development and progression using either primary tumors, transgenic mouse models or tumor-derived cell lines. The identification of many interactors of the MEN1 gene product menin, as well as recurrent chromosomal abnormalities that pinpoint candidate genes of interest will likely result in a better understanding of the molecular pathways involved in insulinoma tumorigenesis. In addition, these studies will pave the way for the identification of novel targets for therapeutical intervention and more reliable markers for clinical diagnosis and prognosis.
Keywords: Insulinoma; EPT; Cell cycle; Progression markers; Candidate genes; Chromosomal aberrations;

Amplification of zinc finger gene 217 (ZNF217) and cancer: When good fingers go bad by Kate G.R. Quinlan; Alexis Verger; Paul Yaswen; Merlin Crossley (333-340).
Chromosome 20q13 is highly amplified in human cancers, including 20–30% of early stage human breast cancers. The amplification correlates with poor prognosis. Over-expression of the zinc-finger protein 217 (ZNF217), a candidate oncogene on 20q13.2, in cultured human mammary and ovarian epithelial cells can lead to their immortalization, indicating that selection for ZNF217 expression may drive 20q13 amplification during critical early stages of cancer progression. ZNF217 can also attenuate apoptotic signals resulting from exposure to doxorubicin, suggesting that ZNF217 expression may also be involved in resistance to chemotherapy. Recent findings indicate that ZNF217 binds specific DNA sequences, recruits the co-repressor C-terminal binding protein (CtBP), and represses the transcription of a variety of genes. Inappropriate expression of ZNF217 may lead to aberrant down-regulation of genes involved in limiting the proliferation, survival, and/or invasiveness of cancer cells. Better understanding of ZNF217 and its associated pathways may provide new targets for therapeutic intervention in human cancers.
Keywords: Zinc finger; Oncogene; Transcriptional repression; Co-repressor complexes;