Gene Targeting Studies In Mice Research Articles

What can we learn from mice lacking pro-survival BCL-2 proteins to advance BH3 mimetic drugs for cancer therapy?

In many human cancers the control of apoptosis is dysregulated, for instance as a result of the overexpression of pro-survival BCL-2 proteins. This promotes tumorigenesis by protecting nascent neoplastic cells from stress and renders malignant cells resistant to anti-cancer agents. Therefore, several BH3 mimetic drugs targeting distinct pro-survival proteins have been developed. The BCL-2 inhibitor Venetoclax/ABT-199, has been approved for treatment of certain blood cancers and tens of thousands of patients have already been treated effectively with this drug. To advance the clinical development of MCL-1 and BCL-XL inhibitors, a more detailed understanding of their distinct and overlapping roles in the survival of malignant as well as non-transformed cells in healthy tissues is required. Here, we discuss similarities and differences in pro-survival BCL-2 protein structure, subcellular localisation and binding affinities to the pro-apoptotic BCL-2 family members. We summarise the findings from gene-targeting studies in mice to discuss the specific roles of distinct pro-survival BCL-2 family members during embryogenesis and the survival of non-transformed cells in healthy tissues in adults. Finally, we elaborate how these findings align with or differ from the observations from the clinical development and use of BH3 mimetic drugs targeting different pro-survival BCL-2 proteins.

Regulation of the germinal center and humoral immunity by interleukin-21

Cytokines play critical roles in regulating the development, survival, differentiation, and function of immune cells. Cytokines exert their function by binding specific receptor complexes on the surface of immune cells and activating intracellular signaling pathways, thereby resulting in induction of specific transcription factors and regulated expression of target genes. While the function of cytokines is often fundamental for the generation of robust and effective immunity following infection or vaccination, aberrant production or function of cytokines can underpin immunopathology. IL-21 is a pleiotropic cytokine produced predominantly by CD4+ T cells. Gene-targeting studies in mice, in vitro analyses of human and murine lymphocytes, and the recent discoveries and analyses of humans with germline loss-of-function mutations in IL21 or IL21R have revealed diverse roles of IL-21 in immune regulation and effector function. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in T cell-dependent B cell activation, germinal center reactions, and humoral immunity and how impaired responses to, or production of, IL-21 can lead to immune dysregulation.

CIDE Proteins in Human Health and Disease.

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

Relative importance of βcyto- and γcyto-actin in primary mouse embryonic fibroblasts.

The highly homologous β (βcyto) and γ (γcyto) cytoplasmic actins are hypothesized to carry out both redundant and unique essential functions, but studies using targeted gene knockout and siRNA-mediated transcript knockdown to examine βcyto- and γcyto-isoform--specific functions in various cell types have yielded conflicting data. Here we quantitatively characterized actin transcript and protein levels, as well as cellular phenotypes, in both gene- and transcript-targeted primary mouse embryonic fibroblasts. We found that the smooth muscle αsm-actin isoform was the dominantly expressed actin isoform in WT primary fibroblasts and was also the most dramatically up-regulated in primary βcyto- or β/γcyto-actin double-knockout fibroblasts. Gene targeting of βcyto-actin, but not γcyto-actin, led to greatly decreased cell proliferation, decreased levels of cellular ATP, and increased serum response factor signaling in primary fibroblasts, whereas immortalization induced by SV40 large T antigen supported fibroblast proliferation in the absence of βcyto-actin. Consistent with in vivo gene-targeting studies in mice, both gene- and transcript-targeting approaches demonstrate that the loss of βcyto-actin protein is more disruptive to primary fibroblast function than is the loss of γcyto-actin.

Interrogating the relevance of mitochondrial apoptosis for vertebrate development and postnatal tissue homeostasis.

"Programmed cell death or 'apoptosis' is critical for organogenesis during embryonic development and tissue homeostasis in the adult. Its deregulation can contribute to a broad range of human pathologies, including neurodegeneration, cancer, or autoimmunity…" These or similar phrases have become generic opening statements in many reviews and textbooks describing the physiological relevance of apoptotic cell death. However, while the role in disease has been documented beyond doubt, facilitating innovative drug discovery, we wonder whether the former is really true. What goes wrong in vertebrate development or in adult tissue when the main route to apoptotic cell death, controlled by the BCL2 family, is impaired? Such scenarios have been mimicked by deletion of one or more prodeath genes within the BCL2 family, and gene targeting studies in mice exploring the consequences have been manifold. Many of these studies were geared toward understanding the role of BCL2 family proteins and mitochondrial apoptosis in disease, whereas fewer focused in detail on their role during normal development or tissue homeostasis, perhaps also due to an irritating lack of phenotype. Looking at these studies, the relevance of classical programmed cell death by apoptosis for development appears rather limited. Together, these many studies suggest either highly selective and context-dependent contributions of mitochondrial apoptosis or significant redundancy with alternative cell death mechanisms, as summarized and discussed here.

GATA4 is a key regulator of steroidogenesis and glycolysis in mouse Leydig cells.

Transcription factor GATA4 is expressed in somatic cells of the mammalian testis. Gene targeting studies in mice have shown that GATA4 is essential for proper differentiation and function of Sertoli cells. The role of GATA4 in Leydig cell development, however, remains controversial, because targeted mutagenesis experiments in mice have not shown a consistent phenotype, possibly due to context-dependent effects or compensatory responses. We therefore undertook a reductionist approach to study the function of GATA4 in Leydig cells. Using microarray analysis and quantitative RT-PCR, we identified a set of genes that are down-regulated or up-regulated after small interfering RNA (siRNA)-mediated silencing of Gata4 in the murine Leydig tumor cell line mLTC-1. These same genes were dysregulated when primary cultures of Gata4(flox/flox) adult Leydig cells were subjected to adenovirus-mediated cre-lox recombination in vitro. Among the down-regulated genes were enzymes of the androgen biosynthetic pathway (Cyp11a1, Hsd3b1, Cyp17a1, and Srd5a). Silencing of Gata4 expression in mLTC-1 cells was accompanied by reduced production of sex steroid precursors, as documented by mass spectrometric analysis. Comprehensive metabolomic analysis of GATA4-deficient mLTC-1 cells showed alteration of other metabolic pathways, notably glycolysis. GATA4-depleted mLTC-1 cells had reduced expression of glycolytic genes (Hk1, Gpi1, Pfkp, and Pgam1), lower intracellular levels of ATP, and increased extracellular levels of glucose. Our findings suggest that GATA4 plays a pivotal role in Leydig cell function and provide novel insights into metabolic regulation in this cell type.

Role of the prion protein family in the gonads.

The prion-gene family comprises four members named PRNP (PRPc), PRND (Doppel), PRNT (PRT), and SPRN (Shadoo). According to species, PRND is located 16–52 kb downstream from the PRNP locus, whereas SPRN is located on another chromosome. The fourth prion-family gene, PRNT, belongs to the same genomic cluster as PRNP and PRND in humans and bovidae. PRNT and PRND possibly resulted from a duplication event of PRND and PRNP, respectively, that occurred early during eutherian species divergence. Although most of the studies concerning the prion-family has been done on PRPc and its involvement in transmissible neurodegenerative disorders, different works report some potential roles of these proteins in the reproductive function of both sexes. Among them, a clear role of PRND, that encodes for the Doppel protein, in male fertility has been demonstrated through gene targeting studies in mice. In other species, Doppel seems to play a role in testis and ovary development but its cellular localization is variable according to the gonadal developmental stage and to the mammalian species considered. For the other three genes, their roles in reproductive function appear ill-defined and/or controversial. The present review aimed to synthesize all the available data on these prion-family members and their relations with reproductive processes, mainly in the gonad of both sexes.

RhoGTPases control specific cytoskeleton‐dependent functions of hematopoietic stem cells

The Rho family of guanosine triphosphatases (GTPases) is composed of members of the Ras superfamily of proteins. They are GTP-bound molecules with a modest intrinsic GTPase activity that can be accelerated upon activation/localization of specialized guanine nucleotide exchange factors. Members of this family act as molecular switches and are required for coordinated cytoskeletal rearrangements that are crucial in a set of specialized functions of mammalian stem cells. These functions include self-renewal, adhesion, and migration. Mouse gene-targeting studies have provided convincing evidence of the indispensable and dispensable roles of individual members of the Rho GTPase family and the putative upstream and downstream mediators in stem cell-specific functions. The role of Rho GTPases and related signaling pathways previously seen in other cell types and organisms have been confirmed in mammalian hematopoietic stem cells (HSCs), and new signaling pathways and unexpected functions unique to HSCs have been identified and dissected. This review summarizes our current understanding of the role of Rho family of GTPases on HSC and progenitor activity through cytoskeleton-mediated signaling pathways, providing insight about relevant signaling pathways that regulate mammalian stem cell self-renewal, adhesion, and migration.

Comparative Proteomic Analysis of Normal and Collagen IX Null Mouse Cartilage Reveals Altered Extracellular Matrix Composition and Novel Components of the Collagen IX Interactome

Collagen IX is an integral cartilage extracellular matrix component important in skeletal development and joint function. Proteomic analysis and validation studies revealed novel alterations in collagen IX null cartilage. Matrilin-4, collagen XII, thrombospondin-4, fibronectin, βig-h3, and epiphycan are components of the in vivo collagen IX interactome. We applied a proteomics approach to advance our understanding of collagen IX ablation in cartilage. The cartilage extracellular matrix is essential for endochondral bone development and joint function. In addition to the major aggrecan/collagen II framework, the interacting complex of collagen IX, matrilin-3, and cartilage oligomeric matrix protein (COMP) is essential for cartilage matrix stability, as mutations in Col9a1, Col9a2, Col9a3, Comp, and Matn3 genes cause multiple epiphyseal dysplasia, in which patients develop early onset osteoarthritis. In mice, collagen IX ablation results in severely disturbed growth plate organization, hypocellular regions, and abnormal chondrocyte shape. This abnormal differentiation is likely to involve altered cell-matrix interactions but the mechanism is not known. To investigate the molecular basis of the collagen IX null phenotype we analyzed global differences in protein abundance between wild-type and knock-out femoral head cartilage by capillary HPLC tandem mass spectrometry. We identified 297 proteins in 3-day cartilage and 397 proteins in 21-day cartilage. Components that were differentially abundant between wild-type and collagen IX-deficient cartilage included 15 extracellular matrix proteins. Collagen IX ablation was associated with dramatically reduced COMP and matrilin-3, consistent with known interactions. Matrilin-1, matrilin-4, epiphycan, and thrombospondin-4 levels were reduced in collagen IX null cartilage, providing the first in vivo evidence for these proteins belonging to the collagen IX interactome. Thrombospondin-4 expression was reduced at the mRNA level, whereas matrilin-4 was verified as a novel collagen IX-binding protein. Furthermore, changes in TGFβ-induced protein βig-h3 and fibronectin abundance were found in the collagen IX knock-out but not associated with COMP ablation, indicating specific involvement in the abnormal collagen IX null cartilage. In addition, the more widespread expression of collagen XII in the collagen IX-deficient cartilage suggests an attempted compensatory response to the absence of collagen IX. Our differential proteomic analysis of cartilage is a novel approach to identify candidate matrix protein interactions in vivo, underpinning further analysis of mutant cartilage lacking other matrix components or harboring disease-causing mutations.

Molecular Cloning ofphd1and Comparative Analysis ofphd1, 2, and3Expression inXenopus laevis

Intensive gene targeting studies in mice have revealed that prolyl hydroxylase domain proteins (PHDs) play important roles in murine embryonic development; however, the expression patterns and function of these genes during embryogenesis of other vertebrates remain largely unknown. Here we report the molecular cloning of phd1 and systematic analysis of phd1, phd2, and phd3 expression in embryos as well as adult tissues of Xenopus laevis. All three phds are maternally provided during Xenopus early development. The spatial expression patterns of phds genes in Xenopus embryos appear to define a distinct synexpression group. Frog phd2 and phd3 showed complementary expression in adult tissues with phd2 transcription levels being high in the eye, brain, and intestine, but low in the liver, pancreas, and kidney. On the contrary, expression levels of phd3 are high in the liver, pancreas, and kidney, but low in the eye, brain, and intestine. All three phds are highly expressed in testes, ovary, gall bladder, and spleen. Among three phds, phd3 showed strongest expression in heart.

A valid mouse model of AGRIN-associated congenital myasthenic syndrome

Congenital myasthenic syndromes (CMS) are inherited diseases affecting the neuromuscular junction (NMJ). Mutations in AGRIN (AGRN) and other genes in the AGRIN signaling pathway cause CMS, and gene targeting studies in mice confirm the importance of this pathway for NMJ formation. However, these mouse mutations are complete loss-of-function alleles that result in an embryonic failure of NMJ formation, and homozygous mice do not survive postpartum. Therefore, mouse models of AGRIN-related CMS that would allow preclinical testing or studies of postnatal disease progression are lacking. Using chemical mutagenesis in mice, we identified a point mutation in Agrn that results in a partial loss-of-function allele, creating a valid model of CMS. The mutation changes phenylalanine 1061 to serine in the SEA domain of AGRIN, a poorly characterized motif shared by other extracellular proteoglycans. NMJs in homozygous mice progressively degrade postnataly. Severity differs with genetic background, in different muscles, and in different regions within a muscle in a pattern matching mouse models of motor neuron disease. Mutant NMJs have decreased acetylcholine receptor density and an increased subsynaptic reticulum, evident by electron microscopy. Synapses eventually denervate and the muscles atrophy. Molecularly, several factors contribute to the partial loss of AGRIN's function. The mutant protein is found at NMJs, but is processed differently than wild-type, with decreased glycosylation, changes in sensitivity to the protease neurotrypsin and other proteolysis, and less efficient externalization and secretion. Therefore, the Agrn point mutation is a model for CMS caused by Agrn mutations and potentially other related neuromuscular diseases.

Stat5: From Breast Development to Cancer Prognosis, Prediction, and Progression

Signal transducer and activator of transcription (STAT) proteins transmit signals from extracellular polypeptides, through transmembrane receptors, directly to target gene promoters in the nucleus resulting in genetic reprogramming of the target cell. There are seven STAT genes in mammals (1, 2, 3, 4, 5A, 5B, and 6) derived phylogenetically from an ancestral gene (Stat93E) that first appeared in Drosophila. STAT proteins are latent transcription factors activated by tyrosine phosphorylation following recruitment to ligand-activated receptor complexes. Tyrosine phosphorylation allows tail-to-tail dimerizationleadingtotheiraccumulationwithinthenucleus.KnockoutofSTAT genes in mice has established their key roles in the distinct responses elicitedbyspecificpolypeptidehormoneligands,withfidelityinresponses being transmitted, in part, through specificity of binding of each STAT Src-homology 2 (SH2) domain to phosphotyrosine-containing motifs located within ligand-activated receptor complexes. Stat5 is encoded by two highly homologous genes—5A and 5B—which, along with Stat3, are clustered on chromosome 17q in humans (chromosome 11 in mice). Gene targeting studies in mice demonstrated interplay between Stat5 and Stat3 in normal breast biology: Stat5A is required for terminal mammary gland differentiation and lactogenesis, while Stat3 is required for breast involution after weaning. Stat5B-deficient mice did not demonstrate a breast phenotype. Constitutively activated STAT proteins, in particular Stat3 and Stat5, have been demonstrated to directly contribute to oncogenesis, in part, by stimulating proliferation and preventing apoptosis in various types of tumor cells. The role for Stat3 and Stat5 in the pathogenesis of human breast cancers is becoming increasingly recognized. There is evidence of increased STAT protein binding in the nuclei of breast cancer compared with the normal tissue of benign lesions. Several studies have shown the role of Stat3 as a prognostic factor in breast cancer. In addition, previous studies have shown an association between Stat5 nuclear localization/ phosphorylation and improved survival. These previous studies that suggest the prognostic significance of Stat5 were conducted in cohorts that previously received some form of adjuvant therapy in a percentage of patients. There have been other published studies that allude to the predictive significance of Stat5. In a study by Yamashita et al, patients with Stat5–positive primary breast tumors had a significantly improved response to endocrine therapy. In the current article by Peck et al accompanying this editorial, a comprehensive study of the utility of Stat5 is comprehensively delineated, including its role as a prognostic marker in the absence of any systemic therapy, in the progression from normal to in situ through invasive ductal cancer and nodal metastases, and finally, as a predictive marker of endocrine resistance. Firstly, the role of Stat5 as a prognostic marker was clearly defined in this article. In two independent cohorts of patients who did not receive adjuvant systemic therapy, phosphorylated and nuclear localized Stat5 (NUC-pYStat5) was found to be an independent marker of outcome in patients with lymph node–negative breast cancer with a total of close to 500 tumor specimens examined. Patients with reduced NUC-pYStat5 expression had approximately a 2.5-fold increase risk of disease recurrence and approximately a 2.4-fold risk of dying of breast cancer. This is the first publication, to our knowledge, that comprehensively addressed the role of NUC-pYStat5 as an independent marker of prognosis in patients with untreated node-negative breast cancer. Secondly, Peck et al define the role of Stat5 in cancer progression. Levels of NUC-pYStat5 quantitated by automated quantitative analysis (AQUA), decreased as the disease progressed from normal to in situ, to invasive, and then to nodal metastases. Thirdly, and perhaps most importantly, Peck et al found that the absence of detectable NUC-pYStat5 in tumors of patients treated with antiestrogen therapy, was associated with poor breast cancer–specific survival. Multivariate analysis showed that patients with the lowest levels of NUC-pYStat5 had nearly a seven-fold increased risk of dying from breast cancer despite antiestrogen therapy. Collectively, these consistent observations strongly suggest that low levels of NUC-pYStat5 are not only a poor prognostic factor that is associated with cancer progression, but also predicts for failure to respond to antiestrogen treatment. This final observation is critically important. Close to one third of patients with estrogen receptor– positive breast cancers fail to respond to antiestrogen therapy as a consequence of either inherent or acquired resistance. Many markers including human epidermal growth factor receptor 2 (HER2) suggest cross-talk between several pathways. However, most of these pathways, including HER2, are poor predictive markers of response to antiestrogen therapy. In contrast, NUC-pYStat5 may add to selecting patients who are unlikely to respond to antiestrogen therapy even though their tumors express estrogen receptor. In conclusion, this work supports the role of Stat5 signaling in cancer progression, and provides strong evidence for this marker as a JOURNAL OF CLINICAL ONCOLOGY E D I T O R I A L S VOLUME 29 NUMBER 18 JUNE 2

Transcriptional Control of Cardiac Fuel Metabolism and Mitochondrial Function

As a persistent pump, the mammalian heart demands a high-capacity mitochondrial system. Significant progress has been made in delineating the gene regulatory networks that control mitochondrial biogenesis and function in striated muscle. The PPARγ coactivator-1 (PGC-1) coactivators serve as inducible boosters of downstream transcription factors that control the expression of genes involved in mitochondrial energy transduction, ATP synthesis, and biogenesis. PGC-1 gain-of-function and loss-of-function studies targeting two PGC-1 family members, PGC-1α and PGC-1β, have provided solid evidence that these factors are both necessary and sufficient for perinatal mitochondrial biogenesis and maintenance of high-capacity mitochondrial function in postnatal heart. In humans, during the development of heart failure owing to hypertension or obesity-related diabetes, the activity of the PGC-1 coactivators, and several downstream target transcription factors, is altered. Gene targeting studies in mice have demonstrated that loss of PGC-1α and PGC-1β in heart leads to heart failure. Interestingly, the pattern of dysregulation within the PGC-1 transcriptional regulatory circuit distinguishes the heart disease caused by hypertension from that caused by diabetes. This transcriptional regulatory cascade and downstream metabolic pathways should be considered as targets for novel etiology-specific therapeutics aimed at the early stages of heart failure.

RhoA GTPase Is Dispensable for Hematopoietic Stem Cell Maintenance but Essential for Multipotent Progenitor and Lower Hierarchical Hematopoietic Differentiation.

AbstractAbstract 2618Rho family small GTPases are critical regulators of multiple functions of blood cells, including adhesion, migration, proliferation, survival and gene expression. Elucidation of their roles in hematopoiesis could be fundamental for understanding the mechanisms of various blood diseases and improving therapeutic outcomes for hematopoietic abnormalities. The Rho GTPases Rac1, Rac2 and Cdc42 have been found essential in maintaining hematopoietic stem cell (HSC) niche residency and regulating myelopoiesis and lymphopoiesis in previous mouse gene targeting studies. Using a dominant-negative mutant overexpression approach, an earlier study showed that suppression of RhoA activity enhanced HSC proliferation and engraftment potential; however, the bone fide role of RhoA in blood development remains unknown given limitations of such a mutant overexpression approach in specificity, dosage effect, and physiological relevance. Here, we stringently define the function of RhoA in HSC maintenance and hematopoiesis using an interferon inducible RhoA conditional knockout mouse model (Mx-cre+; RhoAloxp/loxp). Systematic deletion of RhoA caused lethality of the mice 7 days post polyIC induction due to hematopoietic failure that was accompanied by drastically decreased bone marrow (BM) cellularity (to ∼1/3 of wild type controls), a loss of splenocytes, and a significant reduction of cell counts of most cell lineages in peripheral blood, suggesting RhoA is required for multiple blood cell lineage differentiation and production. Syngenic transplant experiments yielded similar results, demonstrating that these effects are intrinsic to the hematopoietic compartment. The observed cytopenia resulting from RhoA loss was associated with the exhaustion of BM phenotypic HSPC (Lin−Sca1+c-kit+, LSK) and the hierarchical progenitor cells (Lin−c-kit+, LK) in number and frequency, a complete loss of colony forming activities, and a total engraftment failure. In addition, BrdU chase labeling and Annexin V/7-AAD staining revealed that RhoA deletion caused a transient increase of proliferation (1.7 fold increase in S phase) and reduction of survival (16.8 fold reduction in Annexin V− 7-AAD−) of remaining LSK in the BM. These results indicate that RhoA plays an indispensible, cell autonomous role in HSPC maintenance and hematopoiesis. In a competitive transplantation model where Mx-cre+;RhoAloxp/loxp or Mx-cre−;RhoAloxp/loxp CD45.2+ BM cells and WT CD45.1+ competitor cells were transplanted at 1:1 ratio into syngenic CD45.1+ recipients prior to polyIC induction, RhoA deletion also caused a complete extinction of donor derived (CD45.2+) Mac1+Gr1+ myeloid cells, B220+ B cells, as well as CD3+ T cells, in the peripheral. Interestingly, distinct from these more differentiated lineages, BM CD45.2+ LSK population was only marginally affected (88.9 % of pre-polyIC induction level) while the CD45.2+ LK cells and later hierarchical lineages were rapidly eliminated after RhoA deletion in this competitive transplant model. This was associated with increased apoptosis in CD45.2+ RhoA−/− LK, but not LSK, cells, suggesting a specific requirement of RhoA in the myeloid progenitor cell survival. Further, the CD45.2+ RhoA−/− LSK and LSKCD150+ cell populations, not differentiated donor-derived progenitors, from the primary competitive transplant BM, were able to be maintained in secondary transplant recipients 5 months post-transplantation, indicating that RhoA serves as a key regulator at an early progenitor differentiation step. Interestingly, RhoA deletion did not affect lin− cell p-MLC and p-cofilin contents and in vitro expansion in response to SCF stimulation, suggesting that RhoA is not required for actomyosin signaling nor SCF induced proliferation. Taken together, our results implicate RhoA as a unique and essential regulator of multipotent progenitor differentiation and survival that controls multi-lineage hematopoiesis. Disclosures:No relevant conflicts of interest to declare.

Evi-1 as a critical regulator of leukemic cells

Ecotropic viral integration site-1 (EVI-1) has been recognized as one of the dominant oncogenes associated with murine and human myeloid leukemia. Recent clinical studies demonstrated that high EVI-1 expression was an independent negative prognostic indicator of survival in leukemia patients. In addition, gene-targeting studies in mice reveal that Evi-1 is preferentially expressed in hematopoietic stem cells (HSCs) and plays an essential role in proliferation/maintenance of HSCs. Proteins associated with EVI-1, signaling pathways regulated by EVI-1, and downstream mediators of EVI-1 transcriptional regulation have been described and characterized. In this study, we summarize current knowledge regarding biochemical properties and biological functions of EVI-1, which provides a foundation for the development of novel therapeutic strategies.

Transcription factor KLF7 regulates differentiation of neuroectodermal and mesodermal cell lineages

Previous gene targeting studies in mice have implicated the nuclear protein Krüppel-like factor 7 (KLF7) in nervous system development while cell culture assays have documented its involvement in cell cycle regulation. By employing short hairpin RNA (shRNA)-mediated gene silencing, here we demonstrate that murine Klf7 gene expression is required for in vitro differentiation of neuroectodermal and mesodermal cells. Specifically, we show a correlation of Klf7 silencing with down-regulation of the neuronal marker microtubule-associated protein 2 ( Map2) and the nerve growth factor (NGF) tyrosine kinase receptor A ( TrkA) using the PC12 neuronal cell line. Similarly, KLF7 inactivation in Klf7-null mice decreases the expression of the neurogenic marker brain lipid-binding protein/fatty acid-binding protein 7 (BLBP/FABP7) in neural stem cells (NSCs). We also report that Klf7 silencing is detrimental to neuronal and cardiomyocytic differentiation of embryonic stem cells (ESCs), in addition to altering the adipogenic and osteogenic potential of mouse embryonic fibroblasts (MEFs). Finally, our results suggest that genes that are key for self-renewal of undifferentiated ESCs repress Klf7 expression in ESCs. Together with previous findings, these results provide evidence that KLF7 has a broad spectrum of regulatory functions, which reflect the discrete cellular and molecular contexts in which this transcription factor operates.

Rho family GTPases and their regulators in lymphocytes

Rho family GTPases, and the proteins that regulate them, have important roles in many cellular processes, including cell division, survival, migration and adhesion. Although most of our understanding of these proteins has come from studies using cell lines, more recent gene targeting studies in mice are providing insights into the in vivo function of these proteins. Here we review recent progress revealing crucial roles for these proteins in lymphocyte development, activation, differentiation and migration. The emerging picture shows that Rho family GTPases transduce signals from receptors for antigens, chemokines and cytokines, as well as adhesion molecules and pattern recognition receptors, and that they function as focal points for crosstalk between different signalling pathways.

Mammary Tumorigenesis through LPA Receptor Signaling

Lysophosphatidic acid (LPA) is a lipid growth factor that is produced by an extracellular phospholipase, termed autotaxin (ATX), and acts via G protein-coupled receptors. In this issue of Cancer Cell, Liu et al. show that transgenic overexpression of ATX or LPA receptors leads to invasive and metastatic mammary cancer.

Pathogenetic significance of ecotropic viral integration site‐1 in hematological malignancies

The ecotropic viral integration site-1 (Evi-1) gene was first identified as a common locus of retroviral integration in murine leukemia models. In humans, EVI-1 is located on chromosome 3q26, and rearrangements on chromosome 3q26 often activate EVI-1 expression in hematological malignancies. Overexpression of EVI-1 also occurs with high frequency in leukemia patients without 3q26 abnormalities, and importantly, high EVI-1 expression is an independent negative prognostic indicator irrespective of the presence of 3q26 rearrangements. Recent gene targeting studies in mice revealed that Evi-1 is preferentially expressed in hematopoietic stem cells and plays an essential role in proliferation and maintenance of hematopoietic stem cells. In addition, intense attention has been focused on the EVI-1 gene complex as retrovirus integration sites because transcription-activating integrations into the EVI-1 locus confer survival and self-renewing ability to hematopoietic cells. The experimental results using animal models suggest that activation of Evi-1 in hematopoietic cells leads to clonal expansion or dysplastic hematopoiesis, whereas onset of full-blown leukemia requires cooperative genetic events. EVI-1 possesses diverse functions as an oncoprotein, including suppression of transforming growth factor-beta-mediated growth inhibition, upregulation of GATA2, inhibition of the Jun kinase pathway, and stimulation of cell growth via activator protein-1. In this article, we summarize current knowledge regarding the biochemical properties and biological functions of EVI-1 in normal and malignant hematopoiesis, with specific focus on its pathogenetic significance in hematological malignancies.

The LIM-homeodomain transcription factor LMX1B regulates expression of NF-kappa B target genes

LMX1B is a LIM-homeodomain transcription factor essential for development. Putative LMX1B target genes have been identified through mouse gene targeting studies, but their identity as direct LMX1B targets remains hypothetical. We describe here the first molecular characterization of LMX1B target gene regulation. Microarray analysis using a tetracycline-inducible LMX1B expression system in HeLa cells revealed that a subset of NF-κB target genes, including IL-6 and IL-8, are upregulated in LMX1B-expressing cells. Inhibition of NF-κB activity by short interfering RNA-mediated knock-down of p65 impairs, while activation of NF-κB activity by TNF-α synergizes induction of NF-κB target genes by LMX1B. Chromatin immunoprecipitation demonstrated that LMX1B binds to the proximal promoter of IL-6 and IL-8 in vivo, in the vicinity of the characterized κB site, and that LMX1B recruitment correlates with increased NF-κB DNA association. IL-6 promoter–reporter assays showed that the κB site and an adjacent putative LMX1B binding motif are both involved in LMX1B-mediated transcription. Expression of NF-κB target genes is affected in the kidney of Lmx1b −/− knock-out mice, thus supporting the biological relevance of our findings. Together, these data demonstrate for the first time that LMX1B directly regulates transcription of a subset of NF-κB target genes in cooperation with nuclear p50/p65 NF-κB.