Tuba, a GEF for CDC42, links dynamin to actin regulatory proteins

A conserved protein tyrosine phosphatase, PTPN-22, functions in diverse developmental processes in C. elegans

Protein tyrosine phosphatases non-receptor type (PTPNs) have been studied extensively in the context of the adaptive immune system; however, their roles beyond immunoregulation are less well explored. Here we identify novel functions for the conserved C. elegans phosphatase PTPN-22, establishing its role in nematode molting, cell adhesion, and cytoskeletal regulation. Through a non-biased genetic screen, we found that loss of PTPN-22 phosphatase activity suppressed molting defects caused by loss-of-function mutations in the conserved NIMA-related kinases NEKL-2 (human NEK8/NEK9) and NEKL-3 (human NEK6/NEK7), which act at the interface of membrane trafficking and actin regulation. To better understand the functions of PTPN-22, we carried out proximity labeling studies to identify candidate interactors of PTPN-22 during development. Through this approach we identified the CDC42 guanine-nucleotide exchange factor DNBP-1 (human DNMBP) as an in vivo partner of PTPN-22. Consistent with this interaction, loss of DNBP-1 also suppressed nekl-associated molting defects. Genetic analysis, co-localization studies, and proximity labeling revealed roles for PTPN-22 in several epidermal adhesion complexes, including C. elegans hemidesmosomes, suggesting that PTPN-22 plays a broad role in maintaining the structural integrity of tissues. Localization and proximity labeling also implicated PTPN-22 in functions connected to nucleocytoplasmic transport and mRNA regulation, particularly within the germline, as nearly one-third of proteins identified by PTPN-22 proximity labeling are known P granule components. Collectively, these studies highlight the utility of combined genetic and proteomic approaches for identifying novel gene functions.

A conserved protein tyrosine phosphatase, PTPN-22, functions in diverse developmental processes in C. elegans

Protein tyrosine phosphatases non-receptor type (PTPNs) have been studied extensively in the context of the adaptive immune system; however, their roles beyond immunoregulation are less well explored. Here we identify novel functions for the conserved C. elegans phosphatase PTPN-22, establishing its role in nematode molting, cell adhesion, and cytoskeletal regulation. Through a non-biased genetic screen, we found that loss of PTPN-22 phosphatase activity suppressed molting defects caused by loss-of-function mutations in the conserved NIMA-related kinases NEKL-2 (human NEK8/NEK9) and NEKL-3 (human NEK6/NEK7), which act at the interface of membrane trafficking and actin regulation. To better understand the functions of PTPN-22, we carried out proximity labeling studies to identify candidate interactors of PTPN-22 during development. Through this approach we identified the CDC42 guanine-nucleotide exchange factor DNBP-1 (human DNMBP) as an in vivo partner of PTPN-22. Consistent with this interaction, loss of DNBP-1 also suppressed nekl-associated molting defects. Genetic analysis, co-localization studies, and proximity labeling revealed roles for PTPN-22 in several epidermal adhesion complexes, including C. elegans hemidesmosomes, suggesting that PTPN-22 plays a broad role in maintaining the structural integrity of tissues. Localization and proximity labeling also implicated PTPN-22 in functions connected to nucleocytoplasmic transport and mRNA regulation, particularly within the germline, as nearly one-third of proteins identified by PTPN-22 proximity labeling are known P granule components. Collectively, these studies highlight the utility of combined genetic and proteomic approaches for identifying novel gene functions.

Deciphering the Dynamics of Signaling Cascades and Virulence Factors of B. cinerea during Tomato Cell Wall Degradation

The ascomycete Botrytis cinerea is one of the most relevant plant pathogenic fungi, affecting fruits, flowers, and greenhouse-grown crops. The infection strategy used by the fungus comprises a magnificent set of tools to penetrate and overcome plant defenses. In this context, the plant-pathogen communication through membrane receptors and signal transduction cascades is essential to trigger specific routes and the final success of the infection. In previous reports, proteomics approaches to B. cinerea signal transduction cascades changes in response to different carbon source and plant-based elicitors have been performed. Analyzing the secretome, membranome, phosphoproteome, and the phosphomembranome. Moreover, phenotypic changes in fungal biology was analyzed, specifically toxin production. To obtain the whole picture of the process and reveal the network from a system biology approach, this proteomic information has been merged with the phenotypic characterization, to be analyzed using several bioinformatics algorithms (GO, STRING, MCODE) in order to unravel key points in the signal transduction regulation crucial to overcome plant defenses, as well as new virulence/pathogenicity factors that could be used as therapeutic targets in the control of the gray mold rot disease. A total of 1721 and 663 exclusive or overexpressed proteins were identified under glucose (GLU) and deproteinized tomato cell walls (TCW), summarizing all of the protein identifications under phenotypic characterized stages. Under GO analysis, there are more biological process and molecular functions described in GLU, highlighting the increase in signaling related categories. These results agree with the high number of total identified proteins in GLU, probably indicating a more varied and active metabolism of the fungus. When analyzing only GO annotations related with signal transduction, it was revealed that there were proteins related to TOR signaling, the phosphorelay signal transduction system, and inositol lipid-mediated signaling, only under GLU conditions. On the contrary, calcium-mediated signaling GO annotation is only present between the proteins identified under TCW conditions. To establish a potential relationship between expressed proteins, cluster analyses showed 41 and 14 clusters under GLU and TCW conditions, confirming an increase in biological activity in GLU, where we identified a larger number of clusters related to transcription, translation, and cell division, between others. From these analyses, clusters related to signal transduction and clusters related to mycotoxin production were found, which correlated with the phenotypic characterization. The identification of the proteins encompassed in each condition and signal transduction cascade would provide the research community with new information about the B. cinerea infection process and potential candidates of pathogenicity/virulence factors, overcoming plant defenses, and new therapeutic targets.

Tuba Activates Cdc42 during Neuronal Polarization Downstream of the Small GTPase Rab8a

The acquisition of neuronal polarity is a complex molecular process that depends on changes in cytoskeletal dynamics and directed membrane traffic, regulated by the Rho and Rab families of small GTPases, respectively. However, during axon specification, a molecular link that couples these protein families has yet to be identified. In this paper, we describe a new positive feedback loop between Rab8a and Cdc42, coupled by Tuba, a Cdc42-specific guanine nucleotide-exchange factor (GEF), that ensures a single axon generation in rodent hippocampal neurons from embryos of either sex. Accordingly, Rab8a or Tuba gain-of-function generates neurons with supernumerary axons whereas Rab8a or Tuba loss-of-function abrogated axon specification, phenocopying the well-established effect of Cdc42 on neuronal polarity. Although Rab8 and Tuba do not interact physically, the activity of Rab8 is essential to generate a proximal to distal axonal gradient of Tuba in cultured neurons. Tuba-associated and Rab8a-associated polarity defects are also evidenced in vivo, since dominant negative (DN) Rab8a or Tuba knock-down impairs cortical neuronal migration in mice. Our results suggest that Tuba coordinates directed vesicular traffic and cytoskeleton dynamics during neuronal polarization.SIGNIFICANCE STATEMENT The morphologic, biochemical, and functional differences observed between axon and dendrites, require dramatic structural changes. The extension of an axon that is 1 µm in diameter and grows at rates of up to 500 µm/d, demands the confluence of two cellular processes: directed membrane traffic and fine-tuned cytoskeletal dynamics. In this study, we show that both processes are integrated in a positive feedback loop, mediated by the guanine nucleotide-exchange factor (GEF) Tuba. Tuba connects the activities of the Rab GTPase Rab8a and the Rho GTPase Cdc42, ensuring the generation of a single axon in cultured hippocampal neurons and controlling the migration of cortical neurons in the developing brain. Finally, we provide compelling evidence that Tuba is the GEF that mediates Cdc42 activation during the development of neuronal polarity.

BAR domain proteins-a linkage between cellular membranes, signaling pathways, and the actin cytoskeleton

Actin filament assembly typically occurs in association with cellular membranes. A large number of proteins sit at the interface between actin networks and membranes, playing diverse roles such as initiation of actin polymerization, modulation of membrane curvature, and signaling. Bin/Amphiphysin/Rvs (BAR) domain proteins have been implicated in all of these functions. The BAR domain family of proteins comprises a diverse group of multi-functional effectors, characterized by their modular architecture. In addition to the membrane-curvature sensing/inducing BAR domain module, which also mediates antiparallel dimerization, most contain auxiliary domains implicated in protein-protein and/or protein-membrane interactions, including SH3, PX, PH, RhoGEF, and RhoGAP domains. The shape of the BAR domain itself varies, resulting in three major subfamilies: the classical crescent-shaped BAR, the more extended and less curved F-BAR, and the inverse curvature I-BAR subfamilies. Most members of this family have been implicated in cellular functions that require dynamic remodeling of the actin cytoskeleton, such as endocytosis, organelle trafficking, cell motility, and T-tubule biogenesis in muscle cells. Here, we review the structure and function of mammalian BAR domain proteins and the many ways in which they are interconnected with the actin cytoskeleton.

NOSTRIN: A novel modulator of trophoblast giant cell differentiation

Differentiation-dependent expression of NOSTRIN in murine trophoblast cells prompted investigation on NOSTRIN's function in trophoblast differentiation. We show here that NOSTRIN levels increased in both mouse and rat placenta during gestation. NOSTRIN expression was not co-related to expression of eNOS precluding its eNOS mediated function. NOSTRIN transcripts were identified in trophoblast cells of the placenta, predominantly in trophoblast giant cells (TGC). Precocious over-expression of NOSTRIN during differentiation of trophoblast stem cells led to up-regulation of genetic markers associated with invasion (Prl4a1, Prl2a1) and TGC formation (Prl2c2, Prl3d1, Prl3b1). The functional consequence of NOSTRIN over-expression was increased TGC formation and trophoblast cell invasion. Furthermore, number of polyploid TGCs that arise by endoreduplication, were higher in presence of NOSTRIN. Early induction of NOSTRIN was associated with substantial decrease in G/F actin ratio and augmentation of N-WASP-Dynamin-NOSTRIN ternary complex formation that might be partially responsible for nucleation of actin filaments. NOSTRIN also formed a complex with Cdk1 and increased phosphorylation of T14 and Y15 residues that inhibits cytokinesis. Interestingly, SH3 domain deleted NOSTRIN was ineffective in eliciting NOSTRIN's function in differentiating trophoblast cells. These findings demonstrate that NOSTRIN potentiates trophoblast differentiation towards TGC trajectory that is critical for hemochorial placentation.

Development and dynamics of cell polarity at a glance

Cells exhibit morphological and molecular asymmetries that are broadly categorized as cell polarity. The cell polarity established in early embryos prefigures the macroscopic anatomical asymmetries characteristic of adult animals. For example, eggs and early embryos have polarized distributions of RNAs and proteins that generate global anterior/posterior and dorsal/ventral axes. The molecular programs that polarize embryos are subsequently reused in multiple contexts. Epithelial cells require apical/basal polarity to establish their barrier function. Migrating cells polarize in the direction of movement, creating distinct leading and trailing structures. Asymmetrically dividing stem cells partition different molecules between themselves and their daughter cells. Cell polarity can develop de novo, be maintained through rounds of cell division and be dynamically remodeled. In this Cell Science at a Glance review and poster, we describe molecular asymmetries that underlie cell polarity in several cellular contexts. We highlight multiple developmental systems that first establish cell/developmental polarity, and then maintain it. Our poster showcases repeated use of the Par, Scribble and Crumbs polarity complexes, which drive the development of cell polarity in many cell types and organisms. We then briefly discuss the diverse and dynamic changes in cell polarity that occur during cell migration, asymmetric cell division and in planar polarized tissues.

Dynamin Binding Protein (Tuba) Deficiency Inhibits Ciliogenesis and Nephrogenesis in Vitro and in Vivo

Dysfunction of renal primary cilia leads to polycystic kidney disease. We previously showed that the exocyst, a protein trafficking complex, is essential for ciliogenesis and regulated by multiple Rho and Rab family GTPases, such as Cdc42. Cdc42 deficiency resulted in a disruption of renal ciliogenesis and a polycystic kidney disease phenotype in zebrafish and mice. Here we investigate the role of Dynamin binding protein (also known as Tuba), a Cdc42-specific guanine nucleotide exchange factor, in ciliogenesis and nephrogenesis using Tuba knockdown Madin-Darby canine kidney cells and tuba knockdown in zebrafish. Tuba depletion resulted in an absence of cilia, with impaired apical polarization and inhibition of hepatocyte growth factor-induced tubulogenesis in Tuba knockdown Madin-Darby canine kidney cell cysts cultured in a collagen gel. In zebrafish, tuba was expressed in multiple ciliated organs, and, accordingly, tuba start and splice site morphants showed various ciliary mutant phenotypes in these organs. Co-injection of tuba and cdc42 morpholinos at low doses, which alone had no effect, resulted in genetic synergy and led to abnormal kidney development with highly disorganized pronephric duct cilia. Morpholinos targeting two other guanine nucleotide exchange factors not known to be in the Cdc42/ciliogenesis pathway and a scrambled control morpholino showed no phenotypic effect. Given the molecular nature of Cdc42 and Tuba, our data strongly suggest that tuba and cdc42 act in the same ciliogenesis pathway. Our study demonstrates that Tuba deficiency causes an abnormal renal ciliary and morphogenetic phenotype. Tuba most likely plays a critical role in ciliogenesis and nephrogenesis by regulating Cdc42 activity.

The Shp2-induced epithelial disorganization defect is reversed by HDAC6 inhibition independent of Cdc42

Regulation of Shp2, a tyrosine phosphatase, critically influences the development of various diseases. Its role in epithelial lumenogenesis is not clear. Here we show that oncogenic Shp2 dephosphorylates Tuba to decrease Cdc42 activation, leading to the abnormal multi-lumen formation of epithelial cells. HDAC6 suppression reverses oncogenic Shp2-induced multiple apical domains and spindle mis-orientation during division in cysts to acquire normal lumenogenesis. Intriguingly, Cdc42 activity is not restored in this rescued process. We present evidence that simultaneous reduction in myosin II and ERK1/2 activity by HDAC6 inhibition is responsible for the reversion. In HER2-positive breast cancer cells, Shp2 also mediates Cdc42 repression, and HDAC6 inhibition or co-suppression of ERK/myosin II promotes normal epithelial lumen phenotype without increasing Cdc42 activity. Our data suggest a mechanism of epithelial disorganization by Shp2 deregulation, and reveal the cellular context where HDAC6 suppression is capable of establishing normal epithelial lumenogenesis independent of Cdc42.

Cdc42 activity is important for apical-basal epithelial polarity. Here, the authors show that Shp2 disrupts Cdc42 activation, and by reducing the expression of histone deactylase 6, restores epithelial lumen formation in a cdc42-independent manner.

BAR domain proteins regulate Rho GTPase signaling

BAR proteins comprise a heterogeneous group of multi-domain proteins with diverse biological functions. The common denominator is the Bin-Amphiphysin-Rvs (BAR) domain that not only confers targeting to lipid bilayers, but also provides scaffolding to mold lipid membranes into concave or convex surfaces. This function of BAR proteins is an important determinant in the dynamic reconstruction of membrane vesicles, as well as of the plasma membrane. Several BAR proteins function as linkers between cytoskeletal regulation and membrane dynamics. These links are provided by direct interactions between BAR proteins and actin-nucleation-promoting factors of the Wiskott-Aldrich syndrome protein family and the Diaphanous-related formins. The Rho GTPases are key factors for orchestration of this intricate interplay. This review describes how BAR proteins regulate the activity of Rho GTPases, as well as how Rho GTPases regulate the function of BAR proteins. This mutual collaboration is a central factor in the regulation of vital cellular processes, such as cell migration, cytokinesis, intracellular transport, endocytosis, and exocytosis.

Discoidin domain receptor 1 controls linear invadosome formation via a Cdc42-Tuba pathway

In tumor cells, the collagen receptor DDR1 collaborates with Cdc42 and its guanine exchange factor Tuba to promote linear invadosome formation and increase their matrix-invading activity.

Accumulation of type I collagen fibrils in tumors is associated with an increased risk of metastasis. Invadosomes are F-actin structures able to degrade the extracellular matrix. We previously found that collagen I fibrils induced the formation of peculiar linear invadosomes in an unexpected integrin-independent manner. Here, we show that Discoidin Domain Receptor 1 (DDR1), a collagen receptor overexpressed in cancer, colocalizes with linear invadosomes in tumor cells and is required for their formation and matrix degradation ability. Unexpectedly, DDR1 kinase activity is not required for invadosome formation or activity, nor is Src tyrosine kinase. We show that the RhoGTPase Cdc42 is activated on collagen in a DDR1-dependent manner. Cdc42 and its specific guanine nucleotide-exchange factor (GEF), Tuba, localize to linear invadosomes, and both are required for linear invadosome formation. Finally, DDR1 depletion blocked cell invasion in a collagen gel. Altogether, our data uncover an important role for DDR1, acting through Tuba and Cdc42, in proteolysis-based cell invasion in a collagen-rich environment.

Control of Rho GTPase function by BAR-domains

Cytoskeletal dynamics are key to the establishment of cell polarity and the consequent coordination of protrusion and contraction that drives cell migration. During these events, the actin and microtubule cytoskeleton act in concert with the cellular machinery that controls endo-and exocytosis, thus regulating polarized traffic of membranes and membrane-associated proteins. Small GTPases of the Rho family orchestrate cytoskeletal dynamics. Rho GTPase signaling is tightly regulated and mislocalization or constitutive activation may lead to, for example, morphogenetic abnormalities, tumor cell metastasis or apoptosis. There is increasing evidence that traffic to and from the plasma membrane constitutes an important mechanism controlling Rho GTPase activation and signaling. This brief overview discusses a group of proteins that function at the interface between membrane dynamics and RhoGTPase signaling. These proteins all share a so-called BAR domain, which is a lipid and protein binding region that also harbors membrane deforming activity. In the past 15 years, a growing number of BAR domain proteins have been identified and found to regulate Rho GTPase signaling. The studies discussed here define several modes of RhoGTPase regulation through BAR-domain containing proteins, identifying the BAR domain as an important regulatory unit bridging membrane traffic and cytoskeletal dynamics.

Dynamin: expanding its scope to the cytoskeleton

The large GTPase dynamin is well known for its actions on budded cellular membranes to generate vesicles, most often, clathrin-coated endocytic vesicles. The scope of cellular processes in which dynamin-mediated vesicle formation occurs, has expanded to include secretory vesicle formation at the Golgi, from other endosomes and nonclathrin structures, such as caveolae, as well as membrane remodeling during exocytosis and vesicle fusion. An intriguing new facet of dynamin's sphere of influence is the cytoskeleton. Cytoskeletal filament networks maintain cell shape, provide cell movement, execute cell division and orchestrate vesicle trafficking. Recent evidence supports the hypothesis that dynamin influences actin filaments and microtubules via mechanisms that are independent of its membrane-remodeling activities. This chapter discusses this emerging evidence and considers possible mechanisms of action.

Anterior PAR proteins function during cytokinesis and maintain DYN-1 at the cleavage furrow in Caenorhabditis elegans

PAR proteins are key regulators of cellular polarity and have links to the endocytic machinery and the actin cytoskeleton. Our data suggest a unique role for PAR proteins in cytokinesis. We have found that at the onset of cytokinesis, anterior PAR-6 and posterior PAR-2 proteins are redistributed to the furrow membrane in a temporal and spatial manner. PAR-6 and PAR-2 localize to the furrow membrane during ingression but PAR-2-GFP is distinct in that it is excluded from the extreme tip of the furrow. Once the midbody has formed, PAR-2-GFP becomes restricted to the midbody region (the midbody plus the membrane flanking it). Depletion of both anterior PAR proteins, PAR-3 and PAR-6, led to an increase in multinucleate embryos, suggesting that the anterior PAR proteins are necessary during cytokinesis and that PAR-3 and PAR-6 function in cytokinesis may be partially redundant. Lastly, anterior PAR proteins play a role in the maintenance of DYN-1 in the cleavage furrow. Our data indicate that the PAR proteins are involved in the events that occur during cytokinesis and may play a role in promoting the membrane trafficking and remodeling events that occur during this time.

Bridging membrane and cytoskeleton dynamics in the secretory and endocytic pathways

Transport carriers regulate membrane flow between compartments of the secretory and endocytic pathways in eukaryotic cells. Carrier biogenesis is assisted by microtubules, actin filaments and their associated motors that link to membrane-associated coats, adaptors and accessory proteins. We summarize here how the biochemical properties of membranes inform their interactions with cytoskeletal regulators. We also discuss how the forces generated by the cytoskeleton and motor proteins alter the biophysical properties and the shape of membranes. The interplay between the cytoskeleton and membrane proteins ensures tight spatial and temporal control of carrier biogenesis, which is essential for cellular homeostasis.

BAR domain competition during directional cellular migration

While directed cellular migration facilitates the coordinated movement of cells during development and tissue repair, the precise mechanisms regulating the interplay between the extracellular environment, the actin cytoskeleton, and the overlying plasma membrane remain inadequately understood. The BAR domain family of lipid binding, actin cytoskeletal regulators are gaining greater appreciation for their role in these critical processes. BAR domain proteins are involved as both positive and negative regulators of endocytosis, membrane plasticity, and directional cell migration. This review focuses on the functional relationship between different classes of BAR domain proteins and their role in guiding cell migration through regulation of the endocytic machinery. Competition for key signaling substrates by positive and negative BAR domain endocytic regulators appears to mediate control of directional cell migration, and may have wider applicability to other trafficking functions associated with development and carcinogenesis.

Dynamin binding protein gene expression and memory performance in aged rats

Previous studies have shown that messenger RNA (mRNA) of the dynamin-binding protein (DNMBP), a scaffold protein regulating actin cytoskeleton and synaptic vesicle pools, is lower in neuropathologically-confirmed Alzheimer's brains. Here we investigated whether a deficit in long term memory formation during physiological aging is also associated with lower DNMBP expression. Hippocampal DNMBP mRNA was quantified by quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) following inhibitory avoidance task in aged (26- to 27-month-old) rats that, according to memory performance, were ranked as good responders (GR) and bad responders (BR), in adult (3-month-old), late-adult (19-month-old), and aged (26-27-month-old) naive animals. We found that DNMBP mRNA levels were significantly higher in naive adults versus late adult and aged naive rats, in GR versus BR, and in pooled GR and BR versus aged-matched controls. Our data provide the first evidence that hippocampal DNMBP mRNA expression is reduced during physiological aging, and suggest that the capability to increase the expression of this mRNA may be a requirement for preserving long term memory formation during aging.

Constitutive activated Cdc42-associated kinase (Ack) phosphorylation at arrested endocytic clathrin-coated pits of cells that lack dynamin

In cells in which clathrin-mediated endocytosis is arrested before fission by depleting dynamin, the major change in tyrosine phosphorylation is the increased phosphorylation/activation of Ack, a tyrosine kinase. Our finding reveals a link between the progression of clathrin-coated pits to endocytic vesicles and an activation-deactivation cycle of Ack.

Clathrin-mediated endocytosis is a fundamental cellular process conserved from yeast to mammals and is an important endocytic route for the internalization of many specific cargos, including activated growth factor receptors. Here we examined changes in tyrosine phosphorylation, a representative output of growth factor receptor signaling, in cells in which endocytic clathrin-coated pits are frozen at a deeply invaginated state, that is, cells that lack dynamin (fibroblasts from dynamin 1, dynamin 2 double conditional knockout mice). The major change observed in these cells relative to wild-type cells was an increase in the phosphorylation state, and thus activation, of activated Cdc42-associated kinase (Ack), a nonreceptor tyrosine kinase. Ack is concentrated at clathrin-coated pits, and binds clathrin heavy chain via two clathrin boxes. RNA interference–based approaches and pharmacological manipulations further demonstrated that the phosphorylation of Ack requires both clathrin assembly into endocytic clathrin-coated pits and active Cdc42. These findings reveal a link between progression of clathrin-coated pits to endocytic vesicles and an activation–deactivation cycle of Ack.

Membrane-bending proteins

Cellular membranes can assume a number of highly dynamic shapes. Many cellular processes also require transient membrane deformations. Membrane shape is determined by the complex interactions of proteins and lipids. A number of families of proteins that directly bend membranes have been identified. Most associate transiently with membranes and deform them. These proteins work by one or more of three types of mechanisms. First, some bend membranes by inserting amphipathic domains into one of the leaflets of the bilayer; increasing the area of only one leaflet causes the membrane to bend. Second, some proteins form a rigid scaffold that deforms the underlying membrane or stabilizes an already bent membrane. Third, some proteins may deform membranes by clustering lipids or by affecting lipid ordering in membranes. Still other proteins may use novel but poorly understood mechanisms. In this review, we summarize what is known about how different families of proteins bend membranes.

Effect of p53 genotype on gene expression profiles in murine liver

The tumor suppressor protein p53 is a key regulatory element in the cell and is regarded as the "guardian of the genome". Much of the present knowledge of p53 function has come from studies of transgenic mice in which the p53 gene has undergone a targeted deletion. In order to provide additional insight into the impact on the cellular regulatory networks associated with the loss of this gene, microarray technology was utilized to assess gene expression in tissues from both the p53(-/-) and p53(+/-) mice. Six male mice from each genotype (p53(+/+), p53(+/-), and p53(-/-)) were humanely killed and the tissues processed for microarray analysis. The initial studies have been performed in the liver for which the Dunnett test revealed 1406 genes to be differentially expressed between p53(+/+) and p53(+/-) or between p53(+/+) and p53(-/-) at the level of p < or = 0.05. Both genes with increased expression and decreased expression were identified in p53(+/-) and in p53(-/-) mice. Most notable in the gene list derived from the p53(+/-) mice was the significant reduction in p53 mRNA. In the p53(-/-) mice, not only was there reduced expression of the p53 genes on the array, but genes associated with DNA repair, apoptosis, and cell proliferation were differentially expressed, as expected. However, altered expression was noted for many genes in the Cdc42-GTPase pathways that influence cell proliferation. This may indicate that alternate pathways are brought into play in the unperturbed liver when loss or reduction in p53 levels occurs.