Biomedical subjects

Michael M Shen

Publications and source records attributed to Michael M Shen.

At least 19 recordsLinked to original sources

PubMed2026

Nonmuscle-Invasive Recurrence and Management During Surveillance in Patients with Muscle-Invasive Bladder Cancer Who Achieve Clinical Complete Response to Neoadjuvant Chemotherapy.

PURPOSE: Many patients are medically unfit for or refuse radical cystectomy. Few postchemotherapy bladder-sparing active surveillance programs have reported on nonmuscle-invasive recurrences and treatment outcomes. In this study, we present data on nonmuscle-invasive recurrences and their management in this population. MATERIALS AND METHODS: This is a retrospective review of a prospectively maintained database. All patients received cisplatin-based neoadjuvant chemotherapy and were determined to have a clinical complete response (cCR) based on negative endoscopic resection, urine cytology, and cross-sectional imaging. Patient data were entered into a strict active surveillance protocol. Primary outcomes of interest were number of nonmuscle-invasive recurrences, grade and stage, and treatment. Secondary outcomes of interest were nonmuscle-invasive treatment response rate and muscle-invasive and metastatic recurrence rate. RESULTS: A total of 61 cCR patients were identified. In total, 28 patients experienced a median of 1 nonmuscle-invasive recurrence over a median follow-up of 28.3 months. There were a total of 46 nonmuscle-invasive recurrences, including 9 (20%) low-grade recurrences and 37 (80%) high-grade recurrences. Of the 37 high-grade recurrences, the majority (60%) were treated with Bacillus Calmette-Guérin induction. Nonmuscle-invasive recurrence was not associated with later muscle-invasive recurrence or metastasis. Genomic analysis of paired tumor samples demonstrated clonal relatedness in one patient sample while another sample demonstrated a likely precancerous urothelial field effect. CONCLUSIONS: There is a high rate of nonmuscle-invasive recurrences in patients who achieve cCR to neoadjuvant chemotherapy. However, most of these patients may be safely managed with bladder-preserving treatments. These findings emphasize the importance of vigilant surveillance protocols and appropriate patient selection.

bladder cancer↗

PubMed2007

Fibroblast growth factor receptor 2 tyrosine kinase is required for prostatic morphogenesis and the acquisition of strict androgen dependency for adult tissue homeostasis.

The fibroblast growth factor (FGF) family consists of 22 members and regulates a broad spectrum of biological activities by activating diverse isotypes of FGF receptor tyrosine kinases (FGFRs). Among the FGFs, FGF7 and FGF10 have been implicated in the regulation of prostate development and prostate tissue homeostasis by signaling through the FGFR2 isoform. Using conditional gene ablation with the Cre-LoxP system in mice, we demonstrate a tissue-specific requirement for FGFR2 in urogenital epithelial cells--the precursors of prostatic epithelial cells--for prostatic branching morphogenesis and prostatic growth. Most Fgfr2 conditional null (Fgfr2(cn)) embryos developed only two dorsal prostatic (dp) and two lateral prostatic (lp) lobes. This contrasts to wild-type prostate, which has two anterior prostatic (ap), two dp, two lp and two ventral prostatic (vp) lobes. Unlike wild-type prostates, which are composed of well developed epithelial ductal networks, the Fgfr2(cn) prostates, despite retaining a compartmented tissue structure, exhibited a primitive epithelial architecture. Moreover, although Fgfr2(cn) prostates continued to produce secretory proteins in an androgen-dependent manner, they responded poorly to androgen with respect to tissue homeostasis. The results demonstrate that FGFR2 is important for prostate organogenesis and for the prostate to develop into a strictly androgen-dependent organ with respect to tissue homeostasis but not to the secretory function, implying that androgens may regulate tissue homeostasis and tissue function differently. Therefore, Fgfr2(cn) prostates provide a useful animal model for scrutinizing molecular mechanisms by which androgens regulate prostate growth, homeostasis and function, and may yield clues as to how advanced-tumor prostate cells escape strict androgen regulations.

Androgens↗

PubMed2006

Combinatorial activities of Akt and B-Raf/Erk signaling in a mouse model of androgen-independent prostate cancer.

Androgen independence is responsible for most prostate cancer lethality, yet currently there are no effective clinical treatments. We have been investigating the mechanisms underlying androgen-independent prostate cancer in Nkx3.1;Pten mutant mice, which display salient features of the disease, including a requirement for wild-type androgen receptor (AR) signaling. We now demonstrate that the Akt and Erk MAP kinase signaling pathways are activated in androgen-independent lesions of these mice. Forced activation of either Akt or Erk signaling in an androgen-responsive prostate cancer cell line promotes hormone-independent but AR-dependent growth in culture. Although these pathways act additively in culture, they act synergistically in vivo to promote tumorigenicity and androgen independence in the context of the prostate microenvironment. We propose that androgen independence emerges by means of epithelial-stromal competition, in which activation of Akt and Erk promotes AR activity in the prostate epithelium while counteracting antagonistic effects of the stroma.

Androgens↗

PubMed2006

Emergence of androgen independence at early stages of prostate cancer progression in Nkx3.1; Pten mice.

Although androgen deprivation therapy is a widely used treatment for patients with advanced prostate cancer, it ultimately results in the emergence of a hormone-refractory disease that is invariably fatal. To provide insights into the genesis of this disease, we have employed an in vivo model to investigate how and when prostate epithelial cells can acquire the ability to survive and proliferate in the absence of androgens. In particular, we have been studying the evolution of androgen independence in Nkx3.1; Pten mutant mice, which develop prostatic intraepithelial neoplasia and adenocarcinoma as a consequence of aging, as well as androgen-independent phenotypes following castration. We now find that the prostate epithelial cells from these Nkx3.1; Pten mutant mice are capable of surviving and proliferating in the absence of androgens and that they develop androgen-independent phenotypes well before they display overt prostatic intraepithelial neoplasia or cancer phenotypes. Our findings in this mouse model show that acquisition of androgen independence can be uncoupled from overt cancer progression and raise the possibility that hormone-refractory disease can arise at early stages of prostate carcinogenesis.

Aging↗

PubMed2006

The Vg1-related protein Gdf3 acts in a Nodal signaling pathway in the pre-gastrulation mouse embryo.

The formation of the anterior visceral endoderm (AVE) in the pre-gastrulation mouse embryo represents a crucial event in patterning of the anterior-posterior axis. Here, we show that the transforming growth factor beta (Tgfbeta) family member Gdf3 (growth-differentiation factor 3), a close relative of Xenopus Vg1, resembles the Tgfbeta ligand Nodal in both its signaling activity and its role in AVE formation in vivo. Thus, in cell culture, Gdf3 signaling requires the EGF-CFC co-receptor Cripto and can be inhibited by Lefty antagonists. In Xenopus embryos, Gdf3 misexpression results in secondary axis formation, and induces morphogenetic elongation and mesendoderm formation in animal caps. In mouse embryos, Gdf3 is expressed in the inner cell mass and epiblast, and null mutants frequently exhibit abnormal formation or positioning of the AVE. This phenotype correlates with defects in mesoderm and definitive endoderm formation, as well as abnormal Nodal expression levels. Our findings indicate that Gdf3 acts in a Nodal-like signaling pathway in pre-gastrulation development, and provide evidence for the functional conservation of Vg1 activity in mice.

Animals↗

PubMed2006

Conserved regulation and role of Pitx2 in situs-specific morphogenesis of visceral organs.

Pitx2 is expressed in developing visceral organs on the left side and is implicated in left-right (LR) asymmetric organogenesis. The asymmetric expression of Pitx2 is controlled by an intronic enhancer (ASE) that contains multiple Foxh1-binding sites and an Nkx2-binding site. These binding sites are essential and sufficient for asymmetric enhancer activity and are evolutionarily conserved among vertebrates. We now show that mice that lack the ASE of Pitx2 (Pitx2(Delta)(ASE/)(Delta)(ASE) mice) fail to manifest left-sided Pitx2 expression and exhibit laterality defects in most visceral organs, although the position of the stomach and heart looping remain unaffected. Asymmetric Pitx2 expression in some domains, such as the common cardinal vein, was found to be induced by Nodal signaling but to be independent of the ASE of Pitx2. Expression of Pitx2 appears to be repressed in a large portion of the heart ventricle and atrioventricular canal of wild-type mice by a negative feedback mechanism at a time when the gene is still expressed in its other domains. Rescue of the early phase of asymmetric Pitx2 expression in the left lateral plate of Pitx2(Delta)(ASE/)(Delta)(ASE) embryos was not sufficient to restore normal organogenesis, suggesting that continuous expression of Pitx2 in the lineage of the left lateral plate is required for situs-specific organogenesis.

Animals↗

PubMed2005

Non-cell-autonomous role for Cripto in axial midline formation during vertebrate embryogenesis.

Several membrane-associated proteins are known to modulate the activity and range of potent morphogenetic signals during development. In particular, members of the EGF-CFC family encode glycosyl-phosphatidylinositol (GPI)-linked proteins that are essential for activity of the transforming growth factor beta (TGFbeta) ligand Nodal, a factor that plays a central role in establishing the vertebrate body plan. Genetic and biochemical studies have indicated that EGF-CFC proteins function as cell-autonomous co-receptors for Nodal; by contrast, cell culture data have suggested that the mammalian EGF-CFC protein Cripto can act as a secreted signaling factor. Here we show that Cripto acts non-cell-autonomously during axial mesendoderm formation in the mouse embryo and may possess intercellular signaling activity in vivo. Phenotypic analysis of hypomorphic mutants demonstrates that Cripto is essential for formation of the notochordal plate, prechordal mesoderm and foregut endoderm during gastrulation. Remarkably, Cripto null mutant cells readily contribute to these tissues in chimeras, indicating non-cell-autonomy. Consistent with these loss-of-function analyses, gain-of-function experiments in chick embryos show that exposure of node/head process mesoderm to soluble Cripto protein results in alterations in cell fates toward anterior mesendoderm, in a manner that is dependent on Nodal signaling. Taken together, our findings support a model in which Cripto can function in trans as an intercellular mediator of Nodal signaling activity.

Animals↗

PubMed2005

An unusual gene dosage effect of p27kip1 in a mouse model of prostate cancer.

Expression of the p27kip1 cell cycle inhibitor is downregulated in a wide range of carcinomas, yet it is rarely inactivated completely. Our recent studies of a mouse model of prostate carcinogenesis have revealed that cancer progression is enhanced by a two-fold reduction in p27kip1 gene dosage, but is unexpectedly inhibited by further decrease in p27kip1 activity. This paradoxical finding may explain the unusual features of p27kip1 downregulation in human cancer, and also suggests a potential route for therapeutic intervention.

Animals↗

PubMed2005

Two nodal-responsive enhancers control left-right asymmetric expression of Nodal.

Asymmetric expression of Nodal in the lateral plate mesoderm (LPM) plays the major role in left-right (L-R) patterning. A Nodal-responsive enhancer located in the intron 1 (ASE) regulates asymmetric Nodal expression, but it is unknown how Nodal expression is initiated in the left LPM. Here, we have identified a second asymmetric enhancer (left side-specific enhancer, LSE) in the upstream region of mouse Nodal gene. LSE is also located in the corresponding region of human NODAL. L-R specificity of LSE is affected by iv and inv mutations. The requirement of a conserved FoxH1-binding sequence for LSE activity and the dependence of LSE activity on Nodal coreceptor Cryptic indicate that LSE is activated by Nodal signal. However, the mutant mouse lacking LSE does not show obvious L-R patterning defects. These results suggest that Nodal expression in the left LPM is induced by a combination of two Nodal-responsive autoregulatory enhancers, ASE and LSE.

Animals↗

PubMed2005

Context-dependent neuronal differentiation and germ layer induction of Smad4-/- and Cripto-/- embryonic stem cells.

Activation of transforming growth factor-beta (TGF-beta) receptors typically elicits mesodermal development, whereas inhibition of this pathway induces neural fates. In vitro differentiated mouse embryonic stem (ES) cells with deletion of the TGF-beta pathway-related factors Smad4 or Cripto exhibited increased numbers of neurons. Cripto-/- ES cells developed into neuroecto-/epidermal cell types, while Smad4-/- cells also displayed mesodermal differentiation. ES cell differentiation into catecholaminergic neurons showed that these ES cells retained their ability to develop into dopaminergic and serotonergic neurons with typical expression patterns of midbrain and hindbrain genes. In vivo, transplanted ES cells to the mouse striatum became small neuronal grafts, or large grafts with cell types from all germ layers independent of their ES cell genotype. This demonstrates that Smad4-/- and Cripto-/- ES cells favor a neural fate in vitro, but also express the mesodermal phenotype, implying that deletion of either Smad4 or Cripto is not sufficient to block nonneuronal tissue formation.

Animals↗

PubMed2004

A critical role for p27kip1 gene dosage in a mouse model of prostate carcinogenesis.

In human prostate cancer, the frequent down-regulation of p27(kip1) protein expression is correlated with poor clinical outcome, yet p27(kip1) rarely undergoes mutational inactivation. Here, we investigate the consequences of reducing or eliminating p27(kip1) function for prostate carcinogenesis in the context of a mouse modeling lacking the Nkx3.1 homeobox gene and the Pten tumor suppressor. Unexpectedly, we find that triple mutant mice heterozygous for a p27(kip1) null allele (Nkx3.1(+/- or -/-); Pten(+/-); p27(+/-)) display enhanced prostate carcinogenesis, whereas mice that are homozygous null for p27(kip1) (Nkx3.1(+/- or -/-); Pten(+/-); p27(-/-)) show inhibition of cancer progression. Expression profiling reveals that Cyclin D1 is highly up-regulated in compound p27(kip1) heterozygotes, but is down-regulated in the compound p27(kip1) homozygous mutants. Using RNA interference in prostate cancer cell lines with distinct p27(kip1) gene doses, we show that prostate tumorigenicity depends on levels of p27(kip1) and that the consequences of p27(kip1) gene dosage can be attributed, in part, to altered levels of Cyclin D1. Our findings suggest that p27(kip1) possesses dosage-sensitive positive as well as negative modulatory roles in prostate cancer progression.

Animals↗

PubMed2004

A mouse model of classical late-infantile neuronal ceroid lipofuscinosis based on targeted disruption of the CLN2 gene results in a loss of tripeptidyl-peptidase I activity and progressive neurodegeneration.

Mutations in the CLN2 gene, which encodes a lysosomal serine protease, tripeptidyl-peptidase I (TPP I), result in an autosomal recessive neurodegenerative disease of children, classical late-infantile neuronal ceroid lipofuscinosis (cLINCL). cLINCL is inevitably fatal, and there currently exists no cure or effective treatment. In this report, we provide the characterization of the first CLN2-targeted mouse model for cLINCL. CLN2-targeted mice were fertile and apparently healthy at birth despite an absence of detectable TPP I activity. At approximately 7 weeks of age, neurological deficiencies became evident with the onset of a tremor that became progressively more severe and was eventually accompanied by ataxia. Lifespan of the affected mice was greatly reduced (median survival, 138 d), and extensive neuronal pathology was observed including a prominent accumulation of cytoplasmic storage material within the lysosomal-endosomal compartment, a loss of cerebellar Purkinje cells, and widespread axonal degeneration. The CLN2-targeted mouse therefore recapitulates much of the pathology and clinical features of cLINCL and represents an animal model that should provide clues to the normal cellular function of TPP I and the pathogenic processes that underlie neuronal death in its absence. In addition, the CLN2-targeted mouse also represents a valuable model for the evaluation of different therapeutic strategies.

Aminopeptidases↗

PubMed2004

Foxn4 controls the genesis of amacrine and horizontal cells by retinal progenitors.

During vertebrate retinogenesis, seven classes of cells are specified from multipotent progenitors. To date, the mechanisms underlying multipotent cell fate determination by retinal progenitors remain poorly understood. Here, we show that the Foxn4 winged helix/forkhead transcription factor is expressed in a subset of mitotic progenitors during mouse retinogenesis. Targeted disruption of Foxn4 largely eliminates amacrine neurons and completely abolishes horizontal cells, while overexpression of Foxn4 strongly promotes an amacrine cell fate. These results indicate that Foxn4 is both necessary and sufficient for commitment to the amacrine cell fate and is nonredundantly required for the genesis of horizontal cells. Furthermore, we provide evidence that Foxn4 controls the formation of amacrine and horizontal cells by activating the expression of the retinogenic factors Math3, NeuroD1, and Prox1. Our data suggest a model in which Foxn4 cooperates with other key retinogenic factors to mediate the multipotent differentiation of retinal progenitors.

Age Factors↗

PubMed2004

Genetic evidence for nonredundant functional cooperativity between NPC1 and NPC2 in lipid transport.

Niemann-Pick C (NPC) disease is a fatal neurodegenerative disorder characterized by a lysosomal accumulation of cholesterol and other lipids within the cells of patients. Clinically identical forms of NPC disease are caused by defects in either of two different proteins: NPC1, a lysosomal-endosomal transmembrane protein and NPC2, a soluble lysosomal protein with cholesterol binding properties. Although it is clear that NPC1 and NPC2 are required for the egress of lipids from the lysosome, the precise roles of these proteins in this process is unknown. To gain insight into the normal function of NPC2 and to investigate its interactions, if any, with NPC1, we have generated a murine NPC2 hypomorph that expresses 0-4% residual protein in different tissues and have examined its phenotype in the presence and absence of NPC1. The phenotypes of NPC1 and NPC2 single mutants and an NPC1;NPC2 double mutant are similar or identical in terms of disease onset and progression, pathology, neuronal storage, and biochemistry of lipid accumulation. These findings provide genetic evidence that the NPC1 and NPC2 proteins function in concert to facilitate the intracellular transport of lipids from the lysosome to other cellular sites.

Animals↗

PubMed2004

Two modes by which Lefty proteins inhibit nodal signaling.

During vertebrate embryogenesis, members of the Lefty subclass of Transforming Growth Factor-beta (TGFbeta) proteins act as extracellular antagonists of the signaling pathway for Nodal, a TGFbeta-related ligand essential for mesendoderm formation and left-right patterning. Genetic and biochemical analyses have shown that Nodal signaling is mediated by activin receptors but also requires EGF-CFC coreceptors, such as mammalian Cripto or Cryptic. Misexpression experiments in zebrafish and frogs have suggested that Lefty proteins can act as long-range inhibitors for Nodal, possibly through competition for binding to activin receptors. Here we demonstrate two distinct and unexpected mechanisms by which Lefty proteins can antagonize Nodal activity. In particular, using a novel assay for Lefty activity in mammalian cell culture, we find that Lefty can inhibit signaling by Nodal but not by Activin or TGFbeta1, which are EGF-CFC independent. We show that Lefty can interact with Nodal in solution and thereby block Nodal from binding to activin receptors. Furthermore, Lefty can also interact with EGF-CFC proteins and prevent their ability to form part of a Nodal receptor complex. Our results provide mechanistic insights into how Lefty proteins can achieve efficient and stringent regulation of a potent signaling factor.

Activin Receptors↗

PubMed2004

Roles for Hedgehog signaling in androgen production and prostate ductal morphogenesis.

Previous studies have demonstrated that the Hedgehog (Hh) signaling pathway plays a critical role in the development and patterning of many endodermally derived tissues. We have investigated the role of Sonic hedgehog (Shh) in formation of the prostate gland by examining the urogenital phenotype of Shh mutant fetuses. Consistent with earlier work reporting an essential role for Shh in prostate induction, we have found that Shh mutant fetuses display abnormal urogenital development and fail to form prostate buds. Unexpectedly, however, we have discovered that this prostate defect could be rescued by three different methods: renal grafting, explant culture in the presence of androgens, and administration of dihydrotestosterone (DHT) to pregnant mice, indicating that the prostate defect in Shh mutants is due to insufficient levels of androgens. Furthermore, we find that the inhibition of Hh pathway signaling by treatment with cyclopamine does not block prostate formation in explant culture, but instead produces morphological defects consistent with a role for Hh signaling in ductal patterning. Taken together, our studies indicate that the initial organogenesis of the prostate proceeds independently of Shh, but that Shh or other Hh ligands may play a role in subsequent events that pattern the prostate.

Androgens↗

PubMed2003

Distinct modes of floor plate induction in the chick embryo.

To begin to reconcile models of floor plate formation in the vertebrate neural tube, we have performed experiments aimed at understanding the development of the early floor plate in the chick embryo. Using real-time analyses of cell behaviour, we provide evidence that the principal contributor to the early neural midline, the future anterior floor plate, exists as a separate population of floor plate precursor cells in the epiblast of the gastrula stage embryo, and does not share a lineage with axial mesoderm. Analysis of the tissue interactions associated with differentiation of these cells to a floor plate fate reveals a role for the nascent prechordal mesoderm, indicating that more than one inductive event is associated with floor plate formation along the length of the neuraxis. We show that Nr1, a chick nodal homologue, is expressed in the nascent prechordal mesoderm and we provide evidence that Nodal signalling can cooperate with Shh to induce the epiblast precursors to a floor-plate fate. These results indicate that a shared lineage with axial mesoderm cells is not a pre-requisite for floor plate differentiation and suggest parallels between the development of the floor plate in amniote and anamniote embryos.

Animals↗

PubMed2003

Nkx3.1; Pten mutant mice develop invasive prostate adenocarcinoma and lymph node metastases.

Recent studies have shown that several loss-of-function mouse models of prostate carcinogenesis can develop a spectrum of precancerous lesions that resemble human prostatic intraepithelial neoplasia (PIN). Here, we have investigated the malignant potential of the high-grade PIN lesions that form in Nkx3.1(+/-); Pten(+/-) compound mutant mice and demonstrate their neoplastic progression in a serial transplantation/tissue recombination assay. Furthermore, we find that a majority of Nkx3.1(+/-); Pten(+/-) mice greater than 1 year of age develop invasive adenocarcinoma, which is frequently accompanied by metastases to lymph nodes. Finally, we observe androgen independence of high-grade PIN lesions after androgen ablation of Nkx3.1(+/-); Pten(+/-) mice. We conclude that Nkx3.1(+/-); Pten(+/-) mice recapitulate key features of advanced prostate cancer and represent a useful model for investigating associated molecular mechanisms and for evaluating therapeutic approaches.

Adenocarcinoma↗