g Tyrosine phosphorylation-dependent signaling, as mediated by members of the epidermal growth factor receptor (EGFR) family (ErbB1 to -4) of protein tyrosine kinases (PTKs), Src family PTKs (SFKs), and cytokines such as interleukin-6 (IL-6) that signal via signal transducer and activator of transcription 3 (STAT3), is critical to the development and progression of many human breast cancers. EGFR, SFKs, and STAT3 can serve as substrates for the protein tyrosine phosphatase TCPTP (PTPN2). Here we report that TCPTP protein levels are decreased in a subset of breast cancer cell lines in vitro and that TCPTP protein is absent in a large proportion of "triple-negative" primary human breast cancers. Homozygous TCPTP deficiency in murine mammary fat pads in vivo is associated with elevated SFK and STAT3 signaling, whereas TCPTP deficiency in human breast cancer cell lines enhances SFK and STAT3 signaling. On the other hand, TCPTP reconstitution in human breast cancer cell lines severely impaired cell proliferation and suppressed anchorage-independent growth in vitro and xenograft growth in vivo. These studies establish TCPTP's potential to serve as a tumor suppressor in human breast cancer.T he transformation of the breast epithelium to malignant and metastatic disease involves an amalgam of genetic and epigenetic events and is deeply influenced by both estrogen receptor (ER) and growth factor signaling, in particular, that involving the epidermal growth factor receptor (EGFR)/ErbB family of protein tyrosine kinases (PTKs). Breast cancers can be subclassified according to the expression of ER, progesterone receptor (PR), and ErbB2, tumor grade, and transcript profiles (1). Subtypes include (i) luminal A tumors that account for up to 60% of breast cancers and express ER and/or PR but not ErbB2, (ii) luminal B tumors that account for 4% to 19% of breast tumors, express ER or PR, and are highly proliferative and/or express ErbB2, (iii) highly aggressive ErbB2-positive (ErbB2 ϩ ) tumors that are negative for ER and PR (7% to 12% of breast cancers), and (iv) basal-like tumors that account for 14% to 20% of breast cancers and include the so-called "triple-negative" tumors that do not express ErbB2, ER, or PR and are resistant to endocrine-and trastuzumab-based therapies (1).In breast cancer, ErbB2 is amplified and overexpressed in 15% to 20% of primary breast cancers and plays a causal role in mammary carcinogenesis (2). Other EGFR family PTKs implicated in the development of breast cancer include ErbB1, which is activated in many triple-negative tumors and correlates with poor prognosis (3). Although ErbB1 is less transforming than ErbB2 (4), ErbB1 cooperates with the PTK c-Src to promote breast cancer cell migration and anchorage-independent growth and aberrant human mammary epithelial cell acinar formation in threedimensional cultures (5, 6). Elevated c-Src protein levels and/or activity occurs in a striking 70% of primary breast cancers and can coincide with ErbB1 or ErbB2 overexpression (7-9). In ductal carcinoma in sit...

Background: A miRNA precursor generally gives rise to one major miRNA species derived from the 5' arm, and are called miRNA-5p. However, more recent studies have shown co-expression of miRNA-5p and -3p, albeit in different concentrations, in cancer cells targeting different sets of transcripts. Co-expression and regulation of the -5p and -3p miRNA species in stem cells, particularly in the reprogramming process, have not been studied.Methods: In this work, we investigated co-expression and regulation of miRNA-5p and -3p species in human induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs) and embryonic stem cells (ESC) using a nanoliter-scale real-time PCR microarray platform that included 1,036 miRNAs.Results: In comparing iPSC and ESC, only 32 miRNAs were found to be differentially expressed, in agreement of the ESC-like nature of iPSC. In the analysis of reprogramming process in iPSCs, 261 miRNAs were found to be differentially expressed compared with the parental MSC and pre-adipose tissue, indicating significant miRNA alternations in the reprogramming process. In iPSC reprogrammed from MSC, there were 88 miRNAs (33.7%), or 44 co-expressed 5p/3p pairs, clearly indicating frequent co-expression of both miRNA species on reprogramming. Of these, 40 pairs were either co-up- or co-downregulated indicating concerted 5p/3p regulation. The 5p/3p species of only 4 pairs were regulated in reverse directions. Furthermore, some 5p/3p species of the same miRNAs were found to target the same transcript and the same miRNA may cross-target different transcripts of proteins of the G1/S transition of the cell cycle; 5p/3p co-targeting was confirmed in stem-loop RT-PCR.Conclusion: The observed cross- and co-regulation by paired miRNA species suggests a fail-proof scheme of miRNA regulation in iPSC, which may be important to iPSC pluripotency.

CGL (Congenital generalized lipodystrophy) is a genetic disorder characterized by near complete loss of adipose tissue along with increased ectopic fat storage in other organs including liver and muscle. Of the four CGL types, BSCL2 (Berardinelli–Seip Congenital lipodystrophy type 2), resulting from mutations in the BSCL2/seipin gene, exhibits the most severe lipodystrophic phenotype with loss of both metabolic and mechanical adipose depots. The majority of Seipin mutations cause C-terminal truncations, along with a handful of point mutations. Seipin localizes to the ER and is composed of a conserved region including a luminal loop and two transmembrane domains, plus cytosolic N- and C-termini. Animal models deficient in seipin recapitulate the human lipodystrophic phenotype. Cells isolated from seipin knockout mouse models also exhibit impaired adipogenesis. Mechanistically, seipin appears to function as a scaffolding protein to bring together interacting partners essential for lipid metabolism and LD (lipid droplet) formation during adipocyte development. Moreover, cell line and genetic studies indicate that seipin functions in a cell-autonomous manner. Here we will provide a brief overview of the genetic association of the CGLs, and focus on the current understanding of differential contributions of distinct seipin domains to lipid storage and adipogenesis. We will also discuss the roles of seipin-interacting partners, including lipin 1 and 14-3-3β, in mediating seipin-dependent regulation of cellular pathways such as actin cytoskeletal remodelling.

Cell extrusion is a morphogenetic process that is implicated in epithelial homeostasis and elicited by stimuli ranging from apoptosis to oncogenic transformation. To explore if the morphogenetic transcription factor, Snail (SNAI1), induces extrusion, we inducibly expressed a stabilized Snail6SA transgene in confluent MCF-7 monolayers. When expressed in small clusters (<3 cells) within otherwise wild-type confluent monolayers, Snail6SA expression induced apical cell extrusion. In contrast, larger clusters or homogenous cultures of Snail6SA cells did not show enhanced apical extrusion, but eventually displayed sporadic basal delamination. Transcriptomic profiling revealed that Snail6SA did not substantively alter the balance of epithelial: mesenchymal genes. However, we identified a transcriptional network that led to upregulated RhoA signalling and cortical contractility in Snail6SA expressing cells. Enhanced contractility was necessary, but not sufficient, to drive extrusion, suggesting that it collaborates with other factors. Indeed, we found that the transcriptional downregulation of cell-matrix adhesion cooperates with contractility to mediate basal delamination. This provides a pathway for Snail to influence epithelial morphogenesis independently of classic Epithelial to Mesenchymal Transition.