Rationally designed inhibitors identify STAT3 N-domain as a promising anticancer drug target

Activation of the signal transducer and activator of transcription 3 (STAT3) is frequently detected in many cancer types. Activated STAT3 may participate in oncogenesis by stimulating cell proliferation and resisting apoptosis, as well as promoting tumor angiogenesis, invasion, and migration. Many STAT3-dependent cellular responses are mediated through interactions with other proteins, and the amino-terminal domain (N-domain) of STAT3 was proposed to be responsible for this. Our NMR studies revealed that synthetic analogs of the STAT4 second alpha-helix bind to the N-domain and perturb its structure. Structural data available for the STAT4 N-domain was used for the rational design of STAT3 helix 2 analogs with enhanced biological activity. Cell-permeable derivatives of the STAT3 second helix were found to directly and specifically bind to STAT3 but not STAT1 as determined by FRET analysis in cells expressing GFP-STAT3 and GFP-STAT1. Furthermore, they potently induced apoptotic death in breast cancer cells but not normal breast cells or STAT3-deficient fibroblasts. The inhibitors caused significant changes in the mitochondrial potential of cancer cells, leading to cell death. These compounds not only are promising drug candidates but also offer a convenient tool for studying the mechanisms of action of STAT transcription factors and have facilitated our understanding of the crucial role of the N-domain in STAT3 function.

CITED1 expression in Wilms' tumor and embryonic kidney

Wilms' tumors, or nephroblastomas, are thought to arise from abnormal postnatal retention and dysregulated differentiation of nephrogenic progenitor cells that originate as a condensed metanephric mesenchyme within embryonic kidneys. We have previously shown that the transcriptional regulator CITED1 (CBP/p300-interacting transactivators with glutamic acid [E]/aspartic acid [D]-rich C-terminal domain) is expressed exclusively in these nephrogenic progenitor cells and is downregulated as they differentiate to form nephronic epithelia. In the current study, we show that CITED1 expression persists in blastemal cell populations of both experimental rat nephroblastomas and human Wilms' tumors, and that primary human Wilms' tumors presenting with disseminated disease show the highest level of CITED1 expression. Unlike the predominantly cytoplasmic subcellular localization of CITED1 in the normal developing kidney, CITED1 is clearly detectable in the nuclear compartment of Wilms' tumor blastema. These findings indicate that CITED1 is a marker of primitive blastema in Wilms' tumors and suggest that persistent expression and/or altered subcellular localization of CITED1 in the condensed metanephric mesenchyme could play a role in Wilms' tumor initiation and pathogenesis.

Cited1 and Cited2 are differentially expressed in the developing kidney but are not required for nephrogenesis

Early kidney development in mammals is characterized by reciprocal tissue interaction between the ureteric bud and the metanephric mesenchyme. The coordinated response to this interaction is regulated largely at the transcriptional level. Here, we investigate the expression and function of Cited1, a transcriptional cofactor that we have previously implicated in kidney development. We show that Cited1 is expressed in the metanephric mesenchyme after invasion of the ureteric bud and that its expression is limited to the cap mesenchyme, those cells that aggregate most tightly around the tip of the ureteric bud and give rise to nephronic epithelium of the adult kidney. Cited1 is down-regulated during the initial stages of epithelial conversion and is not expressed past this progenitor stage. Despite its unique expression pattern, deletion of Cited1 does not disrupt kidney development. We hypothesized that this finding was due to functional redundancy with other members of this gene family. The expression pattern of Cited2 overlaps that of Cited1, but its deletion, either alone or in combination with Cited1, does not disrupt epithelial differentiation of the metanephric mesenchyme. From these studies, we conclude that Cited1 and 2 are dynamically expressed during kidney development, but are not required for nephrogenesis.

ELR+-CXC chemokines and their receptors in early metanephric development

Although originally identified as mediators of inflammation, it is now apparent that chemokines play a fundamental role in tissue development. In this study, ELR(+)-CXC chemokine family members CXCL2 and CXCL7, along with their preferred receptor CXCR2, were expressed at the earliest stages of metanephric development in the rat, and signaling through this receptor was required for the survival and maintenance of the undifferentiated metanephric mesenchyme (MM). A specific antagonist of the CXCR2 receptor SB225002 induced apoptosis in this population but did not affect more mature structures or cells in the ureteric bud. CXCL7 treatment of isolated MM elicited an angiogenic response by upregulation of matrix metalloprotease 9 and endothelial and mesangial markers (platelet-endothelial cell adhesion molecule, Megsin, Thy-1, PDGF receptor alpha, and vascular alpha-actin) and induced SB225002-sensitive cell invasion through a matrix. Because Wilms' tumor cells may similarly depend on CXCR2 signaling for survival, primary tumor samples were analyzed, and 15 of 16 Wilms' tumors were found to be CXCR2 positive, whereas grossly normal kidney tissues from tumor patients or renal cell carcinomas were CXCR2 negative. Furthermore, cell lines derived from Wilms' tumors but not those from renal cell carcinomas were sensitive to SB225002-induced apoptosis. These data provide evidence for a prosurvival and proangiogenic role of ELR(+)-CXC chemokines and their receptor CXCR2 during metanephric development and suggest a novel mechanism for chemotherapeutic intervention in Wilms' tumor.

Identification of Novel Wilms' Tumor Suppressor Gene Target Genes Implicated in Kidney Development

The Wilms' tumor suppressor gene (WT1) encodes a zinc finger transcription factor that is vital during development of several organs including metanephric kidneys. Despite the critical regulatory role of WT1, the pathways and mechanisms by which WT1 orchestrates development remain elusive. To identify WT1 target genes, we performed a genome-wide expression profiling analysis in cells expressing inducible WT1. We identified a number of direct WT1 target genes, including the epidermal growth factor (EGF)-family ligands epiregulin and HB-EGF, the chemokine CX3CL1, and the transcription factors SLUG and JUNB. The target genes were validated using quantitative reverse transcriptase-polymerase chain reaction, small interfering RNA knockdowns, chromatin immunoprecipitation, and luciferase reporter analyses. Immunohistochemistry of fetal kidneys confirmed that a number of the WT1 target genes had overlapping expression patterns with the highly restricted spatiotemporal expression of WT1. Finally, using an in vitro embryonic kidney culture assay, we found that the addition of recombinant epiregulin, amphiregulin, CX3CL1, and interleukin-11 significantly enhanced ureteric bud branching morphogenesis. Our genome-wide screen implicates WT1 in the transcriptional regulation of the EGF-family of growth factors as well as the CX3CL1 chemokine during nephrogenesis.

Wilms' tumorigenesis is altered by misexpression of the transcriptional co-activator, CITED1

PURPOSE

Wilms' tumors arise from arrested differentiation of renal progenitor cells. CITED1 is a transcriptional regulator that blocks the metanephric mesenchymal-to-epithelial conversion and is expressed in the blastema of both the developing kidney and Wilms' tumors. We hypothesized that alterations of CITED1-dependent signaling promote persistence of blastema and thereby subject these pluripotent cells to future oncogenic events.

METHODS

We used a retroviral delivery system to overexpress the full-length CITED1 (F/L) protein and 2 deletion mutants lacking either of its known functional domains, deltaSID (Smad-4 Interacting Domain) and deltaCR2 (Conserved Region 2; the CITED1 transactivation domain), in a human Wilms' tumor cell line that endogenously expresses CITED1. In vitro effects on cellular proliferation and apoptosis were assayed. In vivo effects on tumorigenesis, growth, proliferation, and apoptosis were determined after heterotransplantation into immunodeficient mice (n = 15 per cell line).

RESULTS

In vitro, overexpression of CITED1-F/L significantly increased, whereas overexpression of the functionally inactivating mutant, CITED1-deltaCR2, significantly reduced cellular proliferation relative to the other lines (P < .0001). In vivo, Wilms' tumor incidence was significantly reduced in animals injected with cells overexpressing the mutant CITED1-deltaCR2 (7%) compared with CITED1-F/L (40%, P = .03) and CITED1-deltaSID (60%, P < .002). Similarly, mean tumor volume was least in the CITED1-deltaCR2 animals when compared with CITED1-F/L (P = .03) and CITED1-deltaSID animals (P < .005). Furthermore, the CITED1-deltaCR2 tumor showed the least cellular proliferation. Misexpression of CITED1 did not affect apoptosis either in vitro or in vivo.

CONCLUSIONS

Overexpression of CITED1 in a human Wilms' tumor cell line significantly increases proliferation in vitro, whereas mutation of its functionally critical transactivation domain (deltaCR2) significantly reduces proliferation. This mutation further perturbs tumorigenesis and tumor growth after heterotransplantation into immunodeficient mice. We speculate that overexpression of CITED1 promotes expansion of a rapidly proliferating population of blastema and thereby induces an unstable environment highly susceptible to future oncogenic events.

Serine-phosphorylated STAT1 is a prosurvival factor in Wilms' tumor pathogenesis

Wilms' tumor (WT), one of the most common pediatric solid cancers, arises in the developing kidney as a result of genetic and epigenetic changes that lead to the abnormal proliferation and differentiation of the metanephric blastema. As activation of signal transducers and activators of transcription (STATs) plays an important role in the maintenance/growth and differentiation of the metanephric blastema, and constitutively activated STATs facilitate neoplastic behaviors of a variety of cancers, we hypothesized that dysregulation of STAT signaling may also contribute to WT pathogenesis. Accordingly, we evaluated STAT phosphorylation patterns in tumors and found that STAT1 was constitutively phosphorylated on serine 727 (S727) in 19 of 21 primary WT samples and two WT cell lines. An inactivating mutation of S727 to alanine reduced colony formation of WT cells in soft agar by more than 80% and induced apoptosis under conditions of growth stress. S727-phosphorylated STAT1 provided apoptotic resistance for WT cells via upregulation of expression of the heat-shock protein (HSP)27 and antiapoptotic protein myeloid cell leukemia (MCL)-1. The kinase responsible for STAT1 S727 phosphorylation in WT cells was identified based upon the use of selective inhibitors as protein kinase CK2, not p38, MAP-kinase kinase (MEK)1/2, phosphatidylinositol 3'-kinase, protein kinase C or Ca/calmodulin-dependent protein kinase II (CaMKII). The inhibition of CK2 blocked the anchorage-independent growth of WT cells and induced apoptosis under conditions of growth stress. Our findings suggest that serine-phosphorylated STAT1, as a downstream target of protein kinase CK2, plays a critical role in the pathogenesis of WT and possibly other neoplasms with similar STAT1 phosphorylation patterns.

Inactivation of FGF8 in early mesoderm reveals an essential role in kidney development

To bypass the essential gastrulation function of Fgf8 and study its role in lineages of the primitive streak, we have used a new mouse line,T-Cre, to generate mouse embryos with pan-mesodermal loss of Fgf8expression. Surprisingly, despite previous models in which Fgf8 has been assigned a pivotal role in segmentation/somite differentiation, Fgf8 is not required for these processes. However, mutant neonates display severe renal hypoplasia with deficient nephron formation. In mutant kidneys, aberrant cell death occurs within the metanephric mesenchyme (MM),particularly in the cortical nephrogenic zone, which provides the progenitors for recurring rounds of nephron formation. Prior to mutant morphological changes, Wnt4 and Lim1 expression, which is essential for nephrogenesis, is absent in MM. Furthermore, comparative analysis of Wnt4-null homozygotes reveals concomitant downregulation of Lim1 and diminished tubule formation. Our data support a model whereby FGF8 and WNT4 function in concert to induce the expression of Lim1 for MM survival and tubulogenesis.

Cited1 Is a Bifunctional Transcriptional Cofactor That Regulates Early Nephronic Patterning

In a screen to identify factors that regulate the conversion of mesenchyme to epithelium during the early stages of nephrogenesis, it was found that the Smad4-interacting transcriptional cofactor, Cited1, is expressed in the condensed cap mesenchyme surrounding the tip of the ureteric bud (UB), is downregulated after differentiation into epithelia, and has the capacity to block UB branching and epithelial morphogenesis in cultured metanephroi. Cited1 represses Wnt/beta-catenin but activates Smad4-dependent transcription involved in TGF-beta and Bmp signaling. By modifying these pathways, Cited1 may coordinate cellular differentiation and survival signals that regulate nephronic patterning in the metanephros.

Cutting Edge: Bone Morphogenetic Protein Antagonists Drm/Gremlin and Dan Interact with Slits and Act as Negative Regulators of Monocyte Chemotaxis

Drm/Gremlin and Dan, two homologous secreted antagonists of bone morphogenic proteins, have been shown to regulate early development, tumorigenesis, and renal pathophysiology. In this study, we report that Drm and Dan physically and functionally interact with Slit1 and Slit2 proteins. Drm binding to Slits depends on its glycosylation and is not interfered with by bone morphogenic proteins. Importantly, Drm and Dan function as inhibitors for monocyte migration induced by stromal cell-derived factor 1alpha (SDF-1alpha) or fMLP. The inhibition of SDF-1alpha-induced monocyte chemotaxis by Dan is not due to blocking the binding of SDF-1alpha to its receptor. Thus, the results identify that Drm and Dan can interact with Slit proteins and act as inhibitors of monocyte chemotaxis, demonstrating a previously unidentified biological role for these proteins.

Renal development: perspectives on a Wnt-dependent process

Specification of embryonic progenitors to generate the branched collecting duct system and tubular epithelia of the nephron in the metanephros is mediated by families of soluble factors that cooperate to regulate morphogenesis. These include multiple members of the FGF, TGF-beta, and Wnt families; however, the complexity of interactions through cell-cell and extracellular matrix-mediated contacts, the redundancy of factors involved, and multiplicity of cooperative signaling mechanisms limit our understanding of events responsible for this development. With available in vitro and targeted mutagenesis models, we are now beginning to comprehend how the secreted inductive proteins and associated transcription factors direct competent cells to produce a functional filtering tubular epithelium and its tightly integrated vascular network.

Conditionally immortalized cell line of inducible metanephric mesenchyme

BACKGROUND

The mesenchymal-epithelial conversion of metanephric mesenchyme (MM) in the formation of nephronic tubules has long served as a paradigm for inductive signaling in morphogenesis. However, the mechanisms underlying this differentiation have remained an enigma due to insufficient numbers of primary mesenchymal cells that must be isolated manually from animal embryos. To overcome this problem, we have established a conditionally immortalized cell line, the rat-inducible metanephric mesenchyme (RIMM-18) by transfection of primary mesenchymal cells with a vector, encoding an estradiol-dependent E1A-ER fusion protein.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), luciferase reporter assay, electrophoretic mobility shift assay, immunocytochemical, and immunohistochemical stainings were used to characterize the established cell line.

RESULTS

We demonstrate that in the presence of estradiol, the RIMM-18 cell line proliferates continuously, maintaining mesenchymal characteristics for over 40 passages. These cells are vimentin-positive and cytokeratin-negative. Under inductive conditions in the absence of estradiol, they are responsive to a number of cytokines, which are established inducers of mesenchymal cells in vivo and in vitro [i.e., fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and transforming growth factor-beta 2 (TGF-beta 2)]. We show the presence in RIMM-18 cells of specific protein markers and functionally active signaling pathways required for induction of tubule formation in MM. Furthermore, induced RIMM-18 cells change morphology, acquiring epithelial-like features, and begin to express epithelial markers (e.g., E-cadherin, cytokeratin, gamma-glutamyl-transpeptidase, and secreted frizzled-related protein 2 (sFRP2).

CONCLUSION

This preliminary characterization of the RIMM-18 cell line suggests that it will be useful in the study of biochemical and molecular mechanisms of nephronic development and, possibly, of some types of renal cancer such as Wilms' tumor, which caricatures the normal process of kidney development.

Early detection of cysteine rich protein 61 (CYR61, CCN1) in urine following renal ischemic reperfusion injury

BACKGROUND

Acute renal failure (ARF) has a high morbidity and mortality. Many therapies have worked in animals but were unsuccessful in clinical trials. The inability to diagnose ARF early may have impaired the success of these trials.

METHOD

We screened a subtraction library to search for potential disease markers that would be induced rapidly after renal injury. Mice and rats were subjected to 30 to 40 minutes of bilateral ischemia.

RESULTS

mRNA for Cyr61, a secreted growth factor-inducible immediate early gene, was markedly up-regulated at two hours in the kidney but not other organs following renal ischemia. In situ hybridization studies suggested Cyr61 was synthesized in the proximal straight tubule. Cyr61 protein was analyzed by capture with heparin beads followed by Western blotting. Induction of Cyr61 protein could be detected in the kidney within one hour, peaked at four to eight hours, and remained elevated for at least 24 hours following ischemia. Cyr61 protein was detected in urine at three to six hours and peaked at six to nine hours after renal injury. Cyr61 was not detected after volume depletion, which is often difficult to differentiate from ARF.

CONCLUSIONS

The secreted, cysteine-rich, heparin binding protein Cyr61 is rapidly induced in proximal straight tubules following renal ischemia, and excreted in the urine where it might serve as an early biomarker of renal injury.

Identification of Glis1, a novel Gli-related, Kruppel-like zinc finger protein containing transactivation and repressor functions

In this study, we describe the identification and characterization of a novel Krüppel-like protein named Gli-similar 1 (Glis1). The Glis1 gene encodes an 84.3-kDa proline-rich protein. Its five tandem zinc finger motifs exhibit highest homology with those of members of the Gli and Zic subfamilies of Krüppel-like proteins. Glis1 was mapped to mouse chromosome 4C6. Northern blot analysis showed that expression of the 3.3-kb Glis1 mRNA is most abundant in placenta and adult kidney and expressed at lower levels in testis. Whole mount in situ hybridization on mouse embryos demonstrated that Glis1 is expressed in a temporal and spatial manner during development; expression was most prominent in several defined structures of mesodermal lineage, including craniofacial regions, branchial arches, somites, vibrissal and hair follicles, limb buds, and myotomes. Confocal microscopic analysis showed that Glis1 is localized to the nucleus. The zinc finger region plays an important role in the nuclear localization of Glis1. Electrophoretic mobility shift assays demonstrated that Glis1 is able to bind oligonucleotides containing the Gli-binding site consensus sequence GACCACCCAC. Although monohybrid analysis showed that in several cell types Glis1 was unable to induce transcription of a reporter, deletion mutant analysis revealed the presence of a strong activation function at the carboxyl terminus of Glis1. The activation through this activation function was totally suppressed by a repressor domain at its amino terminus. Constitutively active Ca(2+)-dependent calmodulin kinase IV enhanced Glis1-mediated transcriptional activation about 4-fold and may be mediated by phosphorylation/activation of a co-activator. Our results suggest that Glis1 may play a critical role in the control of gene expression during specific stages of embryonic development.

Down-regulation of von Hippel-Lindau protein in N-nitroso compound-induced rat non-clear cell renal tumors

Non-clear cell rat kidney tumors, inducible by N-nitroso compounds but lacking mutations in the von Hippel--Lindau (VHL) coding sequence, were examined for other VHL alterations. Neither mutations nor DNA methylation was detected in a putative promoter region. By immunohistochemistry, however, VHL protein level was evidently reduced in six of the eight eosinophilic renal epithelial tumors and in all the ten nephroblastomas. Immunoblotting of normal kidney detected two VHL proteins of 20 and 22kDa in a 16-day-old fetal rat but only 20kDa protein in an adult rat. This is the first demonstration of VHL alteration at the protein level.

TGF beta 2, LIF and FGF2 cooperate to induce nephrogenesis

The metanephric kidney develops from interactions between the epithelial ureteric bud and adjacent metanephric mesenchyme, which is induced by the bud to form the epithelia of the nephron. We have found that leukemia inhibitory factor (LIF) and transforming growth factor beta 2 (TGF beta 2) are secreted by inductive rat bud cells and cooperate to enhance and accelerate renal tubule formation in uninduced rat metanephric mesenchymal explants. LIF alone or TGF beta 2 with fibroblast growth factor 2 induced numerous tubules in isolated mesenchymes over an 8 day period, while (in combination) all three caused abundant tubule formation in 72 hours. Furthermore, neutralization of Wnt ligands with antagonist-secreted Frizzled-related protein 1 abrogated these responses and combinatorial cytokine/growth factor stimulation of explants augmented nuclear activation of Tcf1/Lef1, suggesting that LIF and TGF beta 2/FGF2 cooperate to regulate nephrogenesis through a common Wnt-dependent mechanism.

Secreted Frizzled-related proteins can regulate metanephric development

Wnt-4 signaling plays a critical role in kidney development and is associated with the epithelial conversion of the metanephric mesenchyme. Furthermore, secreted Frizzled-related proteins (sFRPs) that can bind Wnts are normally expressed in the developing metanephros, and function in other systems as modulators of Wnt signaling. sfrp-1 is distributed throughout the medullary and cortical stroma in the metanephros, but is absent from condensed mesenchyme and primitive tubular epithelia of the developing nephron where wnt-4 is highly expressed. In contrast, sfrp-2 is expressed in primitive tubules. To determine their role in kidney development, recombinant sFRP-1, sFRP-2 or combinations of both were applied to cultures of 13-dpc rat metanephroi. Both tubule formation and bud branching were markedly inhibited by sFRP-1, but concurrent sFRP-2 treatment restored some tubular differentiation and bud branching. sFRP-2 itself showed no effect on cultures of metanephroi. In cultures of isolated, induced rat metanephric mesenchymes, sFRP-1 blocked events associated with epithelial conversion (tubulogenesis and expression of lim-1, sfrp-2 and E-cadherin); however, it had no demonstrable effect on early events (compaction of mesenchyme and expression of wt1). As shown herein, sFRP-1 binds Wnt-4 with considerable avidity and inhibits the DNA-binding activity of TCF, an effector of Wnt signaling, while sFRP-2 had no effect on TCF activation. These observations suggest that sFRP-1 and sFRP-2 compete locally to regulate Wnt signaling during renal organogenesis. The antagonistic effect of sFRP-1 may be important either in preventing inappropriate development within differentiated areas of the medulla or in maintaining a population of cortical blastemal cells to facilitate further renal expansion. On the other hand, sFRP-2 might promote tubule formation by permitting Wnt-4 signaling in the presence of sFRP-1.

Mesenchymal-epithelial transition in the developing metanephric kidney: gene expression study by differential display

The developing metanephric kidney is a convenient model to study molecular events associated with epithelial cell differentiation. To determine the genes involved in the defining event of this process, namely, the conversion of metanephric mesenchyme to the epithelium of the nephron, we applied differential display (DD) techniques. Explants of rat metanephric mesenchymes were induced to condense ex vivo with fibroblast growth factor 2 (FGF2) or to form tubules with FGF2 and conditioned medium (CM) from a cell line (RUB1) of ureteric bud, the renal inductive tissue. Three time points (6, 24, and 72 h) were chosen to track the dynamics of gene expression during morphogenesis. Seventy-two up- or down-regulated mRNAs were identified, including 36 novel sequences and those of cell cycle regulatory proteins (TGF-beta2, Cyclin D1, p57Kip2), transcription factors (beta-catenin, Sox11, DP1), signaling proteins (SH3-domain binding protein, G-protein-coupled receptor, Ser-Thr protein kinase), cell adhesion molecules (syndecan-4, integrin-beta1), and also gene33, H19, SM20, IGFBP5, MAMA receptor, lectin, keratin, beta-tubulin, calreticulin, GRP78, ERp72, MnSoD, thioredoxin, and others. Some have previously been associated with kidney development and serve as good controls for expected changes, while most have not been linked with kidney epithelial cell differentiation. Using thin sections of embryonic kidney and labeled antisense RNA probes, we applied RNA hybridization to confirm the results of DD and related the expression of these genes to specific cell lineages of the developing kidney. These results provide a window into the events that mediate this critical differentiation process and suggest that a limited number of interrelated events direct the epithelial conversion of metanephric mesenchyme. genesis 27:22-31, 2000. Published 2000 Wiley-Liss, Inc.

Activation of neu by missense point mutation in the transmembrane domain in schwannomas induced in C3H/HeNCr mice by transplacental exposure to N-nitrosoethylurea

Transplacentally initiated schwannomas in mice and rats arise preferentially in the Gasserian ganglion of the trigeminal nerve and spinal root ganglia, while those of the Syrian golden hamster most commonly occur subcutaneously. Rat and hamster schwannomas almost invariably contain a mutationally activated neu oncogene. In rat schwannomas, the mutant allele predominates, while the relative abundance of mutant alleles is very low in hamster nerve tumors. We investigated whether neu is mutated in mouse schwannomas and whether the pattern and allelic ratio of the mutation resemble those for the hamster or the rat. Pregnant C3H/HeNCr mice received 0.4 micromol N-nitrosoethylurea/g body weight on day 19 of gestation. Ten trigeminal and one peripheral nerve schwannomas developed in 11 of the 201 offspring. Missense T --> A transversion mutations were detected in the neu transmembrane domain in eight of ten schwannomas analyzed, as determined by MnlI digestion of polymerase chain reaction products. The mutant allele was predominantly detected in two tumors and was abundant in six others. Transfection of eight out of ten mouse tumor DNAs into hamster cells yielded transformed foci; seven out of eight contained mutant mouse neu. Mouse schwannomas closely resembled those of rats both in the preferred anatomical site and in the mutant/wild-type neu allele ratios.

neu mutation in schwannomas induced transplacentally in Syrian golden hamsters by N-nitrosoethylurea: high incidence but low allelic representation

Peripheral nerve tumors (PNT) and melanomas induced transplacentally on day 14 of gestation in Syrian golden hamsters by N-nitrosoethylurea were analyzed for activated oncogenes by the NIH 3T3 transfection assay, and for mutations in the neu oncogene by direct sequencing, allele-specific oligonucleotide hybridization, MnlI restriction-fragment-length polymorphism, single-strand conformation polymorphism, and mismatch amplification mutation assays. All (67/67) of the PNT, but none of the melanomas, contained a somatic missense T --> A transversion within the neu oncogene transmembrane domain at a site corresponding to that which also occurs in rat schwannomas transplacentally induced by N-nitrosoethylurea. In only 2 of the 67 individual hamster PNT did the majority of tumor cells appear to carry the mutant neu allele, in contrast to comparable rat schwannomas in which it overwhelmingly predominates. The low fraction of hamster tumor cells carrying the mutation was stable through multiple transplantation passages. In the hamster, as in the rat, specific point-mutational activation of the neu oncogene thus constitutes the major pathway for induction of PNT by transplacental exposure to an alkylating agent, but the low allelic representation of mutant neu in hamster PNT suggests a significant difference in mechanism by which the mutant oncogene acts in this species.

Cell adhesion molecules in the kidney: from embryo to adult

Multiple members from every major family of cell adhesion molecules (CAMs) have been implicated in the development, maintenance, or repair of renal tissues and include several isoforms of integrins, cell-bound glycoproteins, cadherins, immunoglobulin cell adhesion molecules, and selectins. In combination, they mediate a variety of cell-basement membrane and cell-cell interactions believed to direct morphogenesis and cell migration and regulate cell growth and apoptosis, in addition to generating a functional barrier for blood filtration and helping manage inflammatory responses in the kidney. The expression of some CAMs is transient during and critical to normal nephrogenesis, varying with specific stages of development, but often ultimately resulting in the constitutive production of other members in mature tissues. While gene-targeting studies have successfully implicated individual CAMs in renal cell functions, e.g. , alpha3beta1 and alpha8beta1 integrins, the loss of others bears no renal phenotype due to redundancy of homologous family members or to the severity of the defect early in embryogenesis. This review summarizes the studies of various CAMs found in normal embryonic or adult kidney, describes their spatiotemporal expression patterns, and discusses their involvement in renal processes.

Deficient expression of mRNA for the putative inductive factor bone morphogenetic protein-7 in chemically initiated rat nephroblastomas

Wilms' tumor, or nephroblastoma, arises from metanephric blastema and caricatures renal organogenesis. An alteration in at least one of the genes involved in control of renal differentiation is therefore a likely event in tumorigenesis, and indeed some of the genes involved in renal development, for example, hepatocyte growth factor (HGF) and its receptor c-met, the transcription factor Wilms' tumor gene (WT1), and transforming growth factor-beta family member bone morphogenetic protein (BMP)-7, have also been implicated in various models of tumorigenesis. In a comparison of mRNA expression patterns for these genes in normal rat embryonic or fetal kidney and nephroblastoma, we found that the patterns for HGF, met, and WT1 detected by in situ hybridization or ribonuclease protection assay (RPA) in the nephroblastomas were similar to those of normal developing kidney. BMP-7 expression, on the other hand, was lower in most tumors examined both by in situ hybridization and RPA than in normal tissues. This deficiency in a defined inductive factor that has been shown to function in renal tubulogenesis may play a role in tumorigenesis by allowing the accumulation of blastemal populations typical of nephroblastomas.

Epidermal growth factor and transforming growth factor-alpha-associated overexpression of cyclin D1, Cdk4, and c-Myc during hepatocarcinogenesis in Helicobacter hepaticus-infected A/JCr mice

Helicobacter hepaticus is a new bacterial species that is homologous to Helicobacter pylori, a human gastric carcinogen. H. hepaticus causes chronic active hepatitis, with progression to hepatocellular tumors. We hypothesized that chronic up-regulation of epidermal growth factor (EGF), transforming growth factor-alpha, and nuclear oncogenes (cyclin D1 and c-Myc), all known to transform by overexpression, might contribute to tumorigenesis. Livers from mice that were 6-18 months old were analyzed, including nonneoplastic and preneoplastic tissues and tumors, along with age-matched controls, by immunohistochemistry and immunoblotting. EGF and transforming growth factor-alpha were increased at the earliest stage, with a further increase in EGF in tumors. Cyclin D1, cyclin-dependent kinase 4, and c-Myc were strongly increased in all infected livers, with even greater increases in tumors. An increase in cyclin D1/cyclin-dependent kinase 4 complex was also demonstrated in tumors, and its functionality was confirmed by an increase in the hyperphosphorylated:hypophosphorylated retinoblastoma protein ratio. Our findings suggest a possible cooperation of growth factors, cell cycle proteins, and transcription factors during the development of H. hepaticus-associated liver tumors and may have relevance to human cancers associated with bacterial, viral, or parasitic infections.