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Small GTPases belonging to Ras family of proteins have key roles in regulating nearly every aspect of cell biology, such as cell division, cellular differentiation, vesicular transport and localization of cargo proteins, cell morphology, and gene expression. Depending on the extra- cellular signals, Ras family members oscillate between GTP-bound (active) and GDP-bound (inactive) conformations, and in the active form they interact with downstream effector molecules, leading to conformational changes in those effectors. As a result, extracellular signals trigger cellular responses, by means of initiation of a phosphorylation cascade. Functional cycles of Ras family of proteins include interactions with GTPase Activating Proteins (GAPs), and with Guanine Nucleotide Exchange Factors (GEFs) that regulate these small GTPases. GAP proteins activate intrinsic GTP hydrolysis activities of these small G-proteins, and convert active Ras-GTP to inactive Ras-GTP. On the other hand, GEF proteins interact with inactivated Ras-GDP molecules, and convert those inactivated molecules back to activated Ras-GTP, by triggering dissociation of GDP, and reassociation of Ras with GTP which is found at higher concentrations as compared to GDP in the cell cytoplasm. It is well known that mutations in Ras that block these molecules in GTP-bound forms by impairing GTP hydrolysis activity could trigger an uncontrolled and aberrant cellular proliferation. This type of mutations in Ras genes causing uncontrolled activation of the protein, are found in approximately 30% of human cancers overall, and they indicate the significance of mutations in genes encoding Ras family members in cellular proliferation related to de novo oncogenesis in human. [ABSTRACT FROM AUTHOR]

The sodium/iodide symporter mediates active iodide transport in both healthy and cancerous thyroid tissue. By exploiting this activity, radioiodide has been used for decades with considerable success in the detection and treatment of thyroid cancer. Here we show that a specialized form of the sodium/iodide symporter in the mammary gland mediates active iodide transport in healthy lactating (but not in nonlactating) mammary gland and in mammary tumors. In addition to characterizing the hormonal regulation of the mammary gland sodium/iodide symporter, we demonstrate by scintigraphy that mammary adenocarcinomas in transgenic mice bearing Ras or Neu oncogenes actively accumulate iodide by this symporter in vivo. Moreover, more than 80% of the human breast cancer samples we analyzed by immunohistochemistry expressed the symporter, compared with none of the normal (nonlactating) samples from reductive mammoplasties. These results indicate that the mammary gland sodium/iodide symporter may be an essential breast cancer marker and that radioiodide should be studied as a possible option in the diagnosis and treatment of breast cancer. [ABSTRACT FROM AUTHOR]

BACKGROUND: Coiled-coil domain containing protein-124 (Ccdc124) is a putative mRNA-binding factor associated with cell division, and ribosome biology. Previous reports mentioned an up-regulation of CCDC124 gene in cancer, and listed its mRNA in a molecular prognostic signature in breast cancer. OBJECTIVES: Establishing RNA-binding characteristics of Ccdc124 for a better molecular functional characterization, and carrying-out retrospective studies in order to evaluate its aberrant expression in human cancer samples from various tissue origins. METHODS: Bioinformatics calculations followed by RIP and RNA-seq experiments were performed to investigate mRNA targets of Ccdc124. Quantitative studies on arrays of cDNAs from different cancers and IHC assays on tissue arrays were used to assess CCDC124 expression levels in cancers. RESULTS: Ccdc124 was characterized as an RNA-binding protein (RBP) interacting with various mRNAs. CCDC124 mRNA levels were high in tumors, with a particular up-regulation in cancers from esophagus, adrenal gland, endometrium, liver, ovary, thyroid, and urinary bladder. IHC assays indicated strong Ccdc124 positivity in endometrial (95.4%), urinary bladder (68.4%), and ovarian cancers (86.8%). CONCLUSION: Ccdc124 is a cytokinesis related RBP interacting with various mRNAs. CCDC124 mRNA over-expression and an accompanied increase in Ccdc124 protein accumulation was reported in cancers, indicating this RBP as a novel cancer cell marker. [ABSTRACT FROM AUTHOR]

Cytokinetic abscission is the cellular process leading to physical separation of two postmitotic sister cells by severing the intercellular bridge. The most noticeable structural component of the intercellular bridge is a transient organelle termed as midbody, localized at a central region marking the site of abscission. Despite its major role in completion of cytokinesis, our understanding of spatiotemporal regulation of midbody assembly is limited. Here, we report the first characterization of coiled-coil domain-containing protein-124 (Ccdc124), a eukaryotic protein conserved from fungi-to-man, which we identified as a novel centrosomal and midbody protein. Knockdown of Ccdc124 in human HeLa cells leads to accumulation of enlarged and multinucleated cells; however, centrosome maturation was not affected. We found that Ccdc124 interacts with the Ras-guanine nucleotide exchange factor 1B (RasGEF1B), establishing a functional link between cytokinesis and activation of localized Rap2 signaling at the midbody. Our data indicate that Ccdc124 is a novel factor operating both for proper progression of late cytokinetic stages in eukaryotes, and for establishment of Rap2 signaling dependent cellular functions proximal to the abscission site. [ABSTRACT FROM AUTHOR]

Background: Breast cancer is a remarkably heterogeneous disease. Luminal, basal-like, ''normal-like'', and ERBB2+ subgroups were identified and were shown to have different prognoses. The mechanisms underlying this heterogeneity are poorly understood. In our study, we explored the role of cellular differentiation and senescence as a potential cause of heterogeneity. Methodology/Principal Findings: A panel of breast cancer cell lines, isogenic clones, and breast tumors were used. Based on their ability to generate senescent progeny under low-density clonogenic conditions, we classified breast cancer cell lines as senescent cell progenitor (SCP) and immortal cell progenitor (ICP) subtypes. All SCP cell lines expressed estrogen receptor (ER). Loss of ER expression combined with the accumulation of p21Cip1 correlated with senescence in these cell lines. p21Cip1 knockdown, estrogen-mediated ER activation or ectopic ER overexpression protected cells against senescence. In contrast, tamoxifen triggered a robust senescence response. As ER expression has been linked to luminal differentiation, we compared the differentiation status of SCP and ICP cell lines using stem/progenitor, luminal, and myoepithelial markers. The SCP cells produced CD24+ or ER+ luminal-like and ASMA+ myoepithelial-like progeny, in addition to CD44+ stem/progenitor-like cells. In contrast, ICP cell lines acted as differentiation-defective stem/progenitor cells. Some ICP cell lines generated only CD44+/ CD24-/ER-/ASMA- progenitor/stem-like cells, and others also produced CD24+/ER- luminal-like, but not ASMA+ myoepitheliallike cells. Furthermore, gene expression profiles clustered SCP cell lines with luminal A and ''normal-like'' tumors, and ICP cell lines with luminal B and basal-like tumors. The ICP cells displayed higher tumorigenicity in immunodeficient mice. Conclusions/Significance: Luminal A and ''normal-like'' breast cancer cell lines were able to generate luminal-like and myoepithelial-like progeny undergoing senescence arrest. In contrast, luminal B/basal-like cell lines acted as stem/ progenitor cells with defective differentiation capacities. Our findings suggest that the malignancy of breast tumors is directly correlated with stem/progenitor phenotypes and poor differentiation potential. [ABSTRACT FROM AUTHOR]

The highly conserved RasGEF1 family of proteins contain a C-terminal CDC25-Ras exchange motif domain and an N-terminal RasGEF-N domain, and are of unknown function and specificity. Using purified RasGEF1A and RasGEF1B proteins, as well as Ras family proteins, we established that RasGEF1A and RasGEF1B function as very specific exchange factors for Rap2, a member of the Rap subfamily of Ras-like G-proteins. They do not act on Rap1 or other members of the Ras subfamily. Although Rap2 was implicated in the regulation of cell adhesion, the establishment of cell morphology, and the modulation of synapses in neurons, no specific guanine nucleotide exchange factor for Rap2 was previously identified. Using reciprocal site-directed mutagenesis, we analyzed residues that allow RasGEF1 proteins to discriminate between Rap1 and Rap2, and we were able to identify Phe39 in the switch I region of Rap2 as a specificity residue. Mutation of the corresponding Ser39 in Rap1 changed the specificity and allowed the nucleotide exchange of Rap1(S39F) to be stimulated by RasGEF1B. [ABSTRACT FROM AUTHOR]

Abstract: The function of sodium iodide symporter (Na+/I− symporter, or NIS) in mammary epithelial cells is essential for the accumulation of I− in milk; the newborn’s first source of I− for thyroid hormone synthesis. Furthermore, increased mammary gland NIS expression has previously been shown in human breast cancer. Several hormones and factors including all-trans-retinoic acid (tRA) regulate the expression of NIS. In this study, using breast cancer cell lines, we established that tRA-responsive NIS expression is confined to estrogen receptor-α (ERα) positive cells and we investigated the role of ERα in the regulation of NIS expression. We showed that the suppression of endogenous ERα by RNA interference downregulates NIS expression in ERα positive mammary cells. Besides, in an ERα negative cell line, reintroduction of ERα resulted in the expression of NIS in a ligand-independent manner. We also identified a novel estrogen-responsive element in the promoter region of NIS that specifically binds ERα and mediates ERα-dependent activation of transcription. Our results indicate that unliganded ERα (apo-ERα) contributes to the regulation of NIS gene expression. [Copyright &y& Elsevier]