Impaired mammary gland development and function in mice lacking LAR receptor-like tyrosine phosphatase activity

FGF1 supports glycolytic metabolism through the estrogen receptor in endocrine-resistant and obesity-associated breast cancer

BACKGROUND

Obesity increases breast cancer risk and breast cancer-specific mortality, particularly for people with estrogen receptor (ER)-positive tumors. Body mass index (BMI) is used to define obesity, but it may not be the best predictor of breast cancer risk or prognosis on an individual level. Adult weight gain is an independent indicator of breast cancer risk. Our previous work described a murine model of obesity, ER-positive breast cancer, and weight gain and identified fibroblast growth factor receptor (FGFR) as a potential driver of tumor progression. During adipose tissue expansion, the FGF1 ligand is produced by hypertrophic adipocytes as a stimulus to stromal preadipocytes that proliferate and differentiate to provide additional lipid storage capacity. In breast adipose tissue, FGF1 production may stimulate cancer cell proliferation and tumor progression.

METHODS

We explored the effects of FGF1 on ER-positive endocrine-sensitive and resistant breast cancer and compared that to the effects of the canonical ER ligand, estradiol. We used untargeted proteomics, specific immunoblot assays, gene expression profiling, and functional metabolic assessments of breast cancer cells. The results were validated in tumors from obese mice and breast cancer datasets from women with obesity.

RESULTS

FGF1 stimulated ER phosphorylation independently of estradiol in cells that grow in obese female mice after estrogen deprivation treatment. Phospho- and total proteomic, genomic, and functional analyses of endocrine-sensitive and resistant breast cancer cells show that FGF1 promoted a cellular phenotype characterized by glycolytic metabolism. In endocrine-sensitive but not endocrine-resistant breast cancer cells, mitochondrial metabolism was also regulated by FGF1. Comparison of gene expression profiles indicated that tumors from women with obesity shared hallmarks with endocrine-resistant breast cancer cells.

CONCLUSIONS

Collectively, our data suggest that one mechanism by which obesity and weight gain promote breast cancer progression is through estrogen-independent ER activation and cancer cell metabolic reprogramming, partly driven by FGF/FGFR. The first-line treatment for many patients with ER-positive breast cancer is inhibition of estrogen synthesis using aromatase inhibitors. In women with obesity who are experiencing weight gain, locally produced FGF1 may activate ER to promote cancer cell metabolic reprogramming and tumor progression independently of estrogen.

Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty?

Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.

LAR Receptor Tyrosine Phosphatase Family in Healthy and Diseased Brain

Protein phosphatases are major regulators of signal transduction and they are involved in key cellular mechanisms such as proliferation, differentiation, and cell survival. Here we focus on one class of protein phosphatases, the type IIA Receptor-type Protein Tyrosine Phosphatases (RPTPs), or LAR-RPTP subfamily. In the last decade, LAR-RPTPs have been demonstrated to have great importance in neurobiology, from neurodevelopment to brain disorders. In vertebrates, the LAR-RPTP subfamily is composed of three members: PTPRF (LAR), PTPRD (PTPδ) and PTPRS (PTPσ), and all participate in several brain functions. In this review we describe the structure and proteolytic processing of the LAR-RPTP subfamily, their alternative splicing and enzymatic regulation. Also, we review the role of the LAR-RPTP subfamily in neural function such as dendrite and axon growth and guidance, synapse formation and differentiation, their participation in synaptic activity, and in brain development, discussing controversial findings and commenting on the most recent studies in the field. Finally, we discuss the clinical outcomes of LAR-RPTP mutations, which are associated with several brain disorders.

All Good Things Must End: Termination of Receptor Tyrosine Kinase Signal

Receptor tyrosine kinases (RTKs) are membrane receptors that regulate many fundamental cellular processes. A tight regulation of RTK signaling is fundamental for development and survival, and an altered signaling by RTKs can cause cancer. RTKs are localized at the plasma membrane (PM) and the major regulatory mechanism of signaling of RTKs is their endocytosis and degradation. In fact, RTKs at the cell surface bind ligands with their extracellular domain, become active, and are rapidly internalized where the temporal extent of signaling, attenuation, and downregulation are modulated. However, other mechanisms of signal attenuation and termination are known. Indeed, inhibition of RTKs’ activity may occur through the modulation of the phosphorylation state of RTKs and the interaction with specific proteins, whereas antagonist ligands can inhibit the biological responses mediated by the receptor. Another mechanism concerns the expression of endogenous inactive receptor variants that are deficient in RTK activity and take part to inactive heterodimers or hetero-oligomers. The downregulation of RTK signals is fundamental for several cellular functions and the homeostasis of the cell. Here, we will review the mechanisms of signal attenuation and termination of RTKs, focusing on FGFRs.

Protein tyrosine phosphatases in cell adhesion

Adhesive structures between cells and with the surrounding matrix are essential for the development of multicellular organisms. In addition to providing mechanical integrity, they are key signalling centres providing feedback on the extracellular environment to the cell interior, and vice versa. During development, mitosis and repair, cell adhesions must undergo extensive remodelling. Post-translational modifications of proteins within these complexes serve as switches for activity. Tyrosine phosphorylation is an important modification in cell adhesion that is dynamically regulated by the protein tyrosine phosphatases (PTPs) and protein tyrosine kinases. Several PTPs are implicated in the assembly and maintenance of cell adhesions, however, their signalling functions remain poorly defined. The PTPs can act by directly dephosphorylating adhesive complex components or function as scaffolds. In this review, we will focus on human PTPs and discuss their individual roles in major adhesion complexes, as well as Hippo signalling. We have collated PTP interactome and cell adhesome datasets, which reveal extensive connections between PTPs and cell adhesions that are relatively unexplored. Finally, we reflect on the dysregulation of PTPs and cell adhesions in disease.

Genome-wide scan highlights the role of candidate genes on phenotypic plasticity for age at first calving in Nellore heifers

Age at first calving (AFC) plays an important role in the economic efficiency of beef cattle production. This trait can be affected by a combination of genetic and environmental factors, leading to physiological changes in response to heifers’ adaptation to a wide range of environments. Genome-wide association studies through the reaction norm model were carried out to identify genomic regions associated with AFC in Nellore heifers, raised under different environmental conditions (EC). The SNP effects for AFC were estimated in three EC levels (Low, Medium, and High, corresponding to average contemporary group effects on yearling body weight equal to 159.40, 228.6 and 297.6 kg, respectively), which unraveled shared and unique genomic regions for AFC in Low, Medium, and High EC levels, that varied according to the genetic correlation between AFC in different EC levels. The significant genomic regions harbored key genes that might play an important biological role in controlling hormone signaling and metabolism. Shared genomic regions among EC levels were identified on BTA 2 and 14, harboring candidate genes associated with energy metabolism (IGFBP2, IGFBP5, SHOX, SMARCAL1, LYN, RPS20, MOS, PLAG1, CHCD7, and SDR16C6). Gene set enrichment analyses identified important biological functions related to growth, hormone levels affecting female fertility, physiological processes involved in female pregnancy, gamete generation, ovulation cycle, and age at puberty. The genomic regions highlighted differences in the physiological processes linked to AFC in different EC levels and metabolic processes that support complex interactions between the gonadotropic axes and sexual precocity in Nellore heifers.

Towards an Understanding of Synapse Formation

Synapses are intercellular junctions specialized for fast, point-to-point information transfer from a presynaptic neuron to a postsynaptic cell. At a synapse, a presynaptic terminal secretes neurotransmitters via a canonical release machinery, while a postsynaptic specialization senses neurotransmitters via diverse receptors. Synaptic junctions are likely organized by trans-synaptic cell-adhesion molecules (CAMs) that bidirectionally orchestrate synapse formation, restructuring, and elimination. Many candidate synaptic CAMs were described, but which CAMs are central actors and which are bystanders remains unclear. Moreover, multiple genes encoding synaptic CAMs were linked to neuropsychiatric disorders, but the mechanisms involved are unresolved. Here, I propose that engagement of multifarious synaptic CAMs produces parallel trans-synaptic signals that mediate the establishment, organization, and plasticity of synapses, thereby controlling information processing by neural circuits. Among others, this hypothesis implies that synapse formation can be understood in terms of inter- and intracellular signaling, and that neuropsychiatric disorders involve an impairment in such signaling.

Protein tyrosine phosphatase receptor-type δ acts as a negative regulator suppressing breast cancer

Protein tyrosine phosphatase receptor-type δ (PTPRD) is frequently inactivated in human cancers. This study investigated the role of PTPRD in the regulation of stemness, epithelial-mesenchymal transition (EMT), and migration and invasion in breast cancer cells. In vitro, PTPRD silencing using siRNA enhanced the stem cell-like properties of breast cancer cells, including their mammosphere- and holoclone-forming abilities, and it promoted tumorigenicity in vivo. PTPRD knockdown also increased the CD44⁺/CD24⁻ breast cancer stem cell (BCSC) population and the expression of the stem cell markers ALDH1 and OCT4. It also promoted migration and invasion by breast cancer cell, EMT, and activation of signal transducer and activator of transcription 3 (STAT3). BCSCs expressed low levels of PTPRD, displayed mesenchymal phenotypes, and were more sensitive to IL-6-mediated STAT3 activation than non-BCSCs. PTPRD expression was upregulated by IL-6 in breast cancer cells, thereby establishing a negative feedback circuit by which IL-6 induced canonical STAT3 phosphorylation and transiently upregulated PTPRD, which in turn dephosphorylated STAT3 and prevented downstream signaling via the IL-6/STAT3 cascade. These data suggest that therapies aimed at restoring or enhancing PTPRD expression may be effective in controlling breast cancer progression and metastasis.

A patient with van Maldergem syndrome with endocrine abnormalities, hypogonadotropic hypogonadism, and breast aplasia/hypoplasia

Background

We report a female patient with endocrine abnormalities, hypogonadotropic hypogonadism and amazia (breasts aplasia/hypoplasia but normal nipples and areolas) in a rare syndrome: Van Maldergem syndrome (VMS).

Case presentation

Our patient was first evaluated at age 4 for intellectual disability, craniofacial features, and auditory malformations. At age 15, she presented with no breast development and other findings consistent with hypogonadotropic hypogonadism. At age 37, she underwent whole exome sequencing (WES) to identify pathogenic variants. WES revealed compound heterozygous variants in DCHS1 (rs145099391:G > A, p.P197L & rs753548138:G > A, p.T2334 M) [RefSeq NM_003737.3], diagnostic of Van Maldergem syndrome (VMS-1). VMS is a rare autosomal disorder reported in only 13 patients, characterized by intellectual disability, typical craniofacial features, auditory malformations, hearing loss, skeletal and limb malformations, brain abnormalities with periventricular neuronal heterotopia and other variable anomalies. Our patient had similar phenotypic abnormalities. She also had hypogonadotropic hypogonadism and amazia. Based on the clinical findings reported, two previously published patients with VMS may also have been affected by hypogonadotropic hypogonadism, but endocrine abnormalities were not evaluated or mentioned.

Conclusion

This case highlights an individual with VMS, characterized by compound heterozygous variants in DCHS1. Our observations may provide additional information on the phenotypic spectrum of VMS, including hypogonadotropic hypogonadism and amazia. However, the molecular genetic basis for endocrine anomalies observed in some VMS patients, including ours, remains unexplained.

Electronic supplementary material

The online version of this article (10.1186/s13633-017-0052-z) contains supplementary material, which is available to authorized users.

Regulation of Platelet Derived Growth Factor Signaling by Leukocyte Common Antigen-related (LAR) Protein Tyrosine Phosphatase: A Quantitative Phosphoproteomics Study

Intracellular signaling pathways are reliant on protein phosphorylation events that are controlled by a balance of kinase and phosphatase activity. Although kinases have been extensively studied, the role of phosphatases in controlling specific cell signaling pathways has been less so. Leukocyte common antigen-related protein (LAR) is a member of the LAR subfamily of receptor-like protein tyrosine phosphatases (RPTPs). LAR is known to regulate the activity of a number of receptor tyrosine kinases, including platelet-derived growth factor receptor (PDGFR). To gain insight into the signaling pathways regulated by LAR, including those that are PDGF-dependent, we have carried out the first systematic analysis of LAR-regulated signal transduction using SILAC-based quantitative proteomic and phosphoproteomic techniques. We haveanalyzed differential phosphorylation between wild-type mouse embryo fibroblasts (MEFs) and MEFs in which the LAR cytoplasmic phosphatase domains had been deleted (LARΔP), and found a significant change in abundance of phosphorylation on 270 phosphosites from 205 proteins because of the absence of the phosphatase domains of LAR. Further investigation of specific LAR-dependent phosphorylation sites and enriched biological processes reveal that LAR phosphatase activity impacts on a variety of cellular processes, most notably regulation of the actin cytoskeleton. Analysis of putative upstream kinases that may play an intermediary role between LAR and the identified LAR-dependent phosphorylation events has revealed a role for LAR in regulating mTOR and JNK signaling.

LAR protein tyrosine phosphatase regulates focal adhesions via CDK1

Focal adhesions are complex multi-molecular structures that link the actin cytoskeleton to the extracellular matrix via integrin adhesion receptors and play a key role in regulation of many cellular functions. LAR is a receptor protein tyrosine phosphatase that regulates PDGF signalling and localises to focal adhesions. We have observed that loss of LAR phosphatase activity in mouse embryonic fibroblasts results in reduced numbers of focal adhesions and decreased adhesion to fibronectin. To understand how LAR regulates cell adhesion we used phosphoproteomic data, comparing global phosphorylation events in wild type and LAR phosphatase-deficient cells, to analyse differential kinase activity. Kinase prediction analysis of LAR-regulated phosphosites identified a node of cytoskeleton- and adhesion-related proteins centred on cyclin-dependent kinase-1 (CDK1). We found that loss of LAR activity resulted in reduced activity of CDK1, and that CDK1 activity was required for LAR-mediated focal adhesion complex formation. We also established that LAR regulates CDK1 activity via c-Abl and PKB/Akt. In summary, we have identified a novel role for a receptor protein tyrosine phosphatase in regulating CDK1 activity and hence cell adhesion to the extracellular matrix.

A Synthetic Lethal Screen Identifies a Role for Lin-44/Wnt in C. elegans Embryogenesis

BACKGROUND

The C. elegans proteins PTP-3/LAR-RPTP and SDN-1/Syndecan are conserved cell adhesion molecules. Loss-of-function (LOF) mutations in either ptp-3 or sdn-1 result in low penetrance embryonic developmental defects. Work from other systems has shown that syndecans can function as ligands for LAR receptors in vivo. We used double mutant analysis to test whether ptp-3 and sdn-1 function in a linear genetic pathway during C. elegans embryogenesis.

RESULTS

We found animals with LOF in both sdn-1 and ptp-3 exhibited a highly penetrant synthetic lethality (SynLet), with only a small percentage of animals surviving to adulthood. Analysis of the survivors demonstrated that these animals had a synergistic increase in the penetrance of embryonic developmental defects. Together, these data strongly suggested PTP-3 and SDN-1 function in parallel during embryogenesis. We subsequently used RNAi to knockdown ~3,600 genes predicted to encode secreted and/or transmembrane molecules to identify genes that interacted with ptp-3 or sdn-1. We found that the Wnt ligand, lin-44, was SynLet with sdn-1, but not ptp-3. We used 4-dimensional time-lapse analysis to characterize the interaction between lin-44 and sdn-1. We found evidence that loss of lin-44 caused defects in the polarization and migration of endodermal precursors during gastrulation, a previously undescribed role for lin-44 that is strongly enhanced by the loss of sdn-1.

CONCLUSIONS

PTP-3 and SDN-1 function in compensatory pathways during C. elegans embryonic and larval development, as simultaneous loss of both genes has dire consequences for organismal survival. The Wnt ligand lin-44 contributes to the early stages of gastrulation in parallel to sdn-1, but in a genetic pathway with ptp-3. Overall, the SynLet phenotype provides a robust platform to identify ptp-3 and sdn-1 interacting genes, as well as other genes that function in development, yet might be missed in traditional forward genetic screens.

Missing-in-Metastasis regulates cell motility and invasion via PTPδ-mediated changes in SRC activity

MIM (Missing-in-Metastasis), also known as MTSS1 (metastasis suppressor 1), is a scaffold protein that is down-regulated in multiple metastatic cancer cell lines compared with non-metastatic counterparts. MIM regulates cytoskeletal dynamics and actin polymerization, and has been implicated in the control of cell motility and invasion. MIM has also been shown to bind to a receptor PTP (protein tyrosine phosphatase), PTPδ, an interaction that may provide a link between tyrosine-phosphorylation-dependent signalling and metastasis. We used shRNA-mediated gene silencing to investigate the consequences of loss of MIM on the migration and invasion of the MCF10A mammary epithelial cell model of breast cancer. We observed that suppression of MIM by RNAi enhanced migration and invasion of MCF10A cells, effects that were associated with increased levels of PTPδ. Furthermore, analysis of human clinical data indicated that PTPδ was elevated in breast cancer samples when compared with normal tissue. We demonstrated that the SRC protein tyrosine kinase is a direct substrate of PTPδ and, upon suppression of MIM, we observed changes in the phosphorylation status of SRC; in particular, the inhibitory site (Tyr527) was hypophosphorylated, whereas the activating autophosphorylation site (Tyr416) was hyperphosphorylated. Thus the absence of MIM led to PTPδ-mediated activation of SRC. Finally, the SRC inhibitor SU6656 counteracted the effects of MIM suppression on cell motility and invasion. The present study illustrates that both SRC and PTPδ have the potential to be therapeutic targets for metastatic tumours associated with loss of MIM.

Homozygous truncating PTPRF mutation causes athelia

Athelia is a very rare entity that is defined by the absence of the nipple-areola complex. It can affect either sex and is mostly part of syndromes including other congenital or ectodermal anomalies, such as limb-mammary syndrome, scalp-ear-nipple syndrome, or ectodermal dysplasias. Here, we report on three children from two branches of an extended consanguineous Israeli Arab family, a girl and two boys, who presented with a spectrum of nipple anomalies ranging from unilateral hypothelia to bilateral athelia but no other consistently associated anomalies except a characteristic eyebrow shape. Using homozygosity mapping after single nucleotide polymorphism (SNP) array genotyping and candidate gene sequencing we identified a homozygous frameshift mutation in PTPRF as the likely cause of nipple anomalies in this family. PTPRF encodes a receptor-type protein phosphatase that localizes to adherens junctions and may be involved in the regulation of epithelial cell-cell contacts, peptide growth factor signaling, and the canonical Wnt pathway. Together with previous reports on female mutant Ptprf mice, which have a lactation defect, and disruption of one allele of PTPRF by a balanced translocation in a woman with amastia, our results indicate a key role for PTPRF in the development of the nipple-areola region.

Inactivation of LAR family phosphatase genes Ptprs and Ptprf causes craniofacial malformations resembling Pierre-Robin sequence

Leukocyte antigen related (LAR) family receptor protein tyrosine phosphatases (RPTPs) regulate the fine balance between tyrosine phosphorylation and dephosphorylation that is crucial for cell signaling during development and tissue homeostasis. Here we show that LAR RPTPs are required for normal development of the mandibular and maxillary regions. Approximately half of the mouse embryos lacking both Ptprs (RPTPσ) and Ptprf (LAR) exhibit micrognathia (small lower jaw), cleft palate and microglossia/glossoptosis (small and deep tongue), a phenotype closely resembling Pierre-Robin sequence in humans. We show that jaw bone and cartilage patterning occurs aberrantly in LAR family phosphatase-deficient embryos and that the mandibular arch harbors a marked decrease in cell proliferation. Analysis of signal transduction in embryonic tissues and mouse embryonic fibroblast cultures identifies an increase in Bmp-Smad signaling and an abrogation of canonical Wnt signaling associated with loss of the LAR family phosphatases. A reactivation of β-catenin signaling by chemical inhibition of GSK3β successfully resensitizes LAR family phosphatase-deficient cells to Wnt induction, indicating that RPTPs are necessary for normal Wnt/β-catenin pathway activation. Together these results identify LAR RPTPs as important regulators of craniofacial morphogenesis and provide insight into the etiology of Pierre-Robin sequence.

Protein tyrosine phosphatases as novel targets in breast cancer therapy

Breast cancer is linked to hyperactivation of protein tyrosine kinases (PTKs), and recent studies have unveiled that selective tyrosine dephosphorylation by protein tyrosine phosphatases (PTPs) of specific substrates, including PTKs, may activate or inactivate oncogenic pathways in human breast cancer cell growth-related processes. Here, we review the current knowledge on the involvement of PTPs in breast cancer, as major regulators of breast cancer therapy-targeted PTKs, such as HER1/EGFR, HER2/Neu, and Src. The functional interplay between PTKs and PTK-activating or -inactivating PTPs, and its implications in novel breast cancer therapies based on targeting of specific PTPs, are discussed.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Leukocyte antigen-related inhibition attenuates palmitate-induced insulin resistance in muscle cells

Palmitate has been shown to induce insulin resistance in skeletal muscle cells. The aim of this study was to investigate the role of the leukocyte common antigen-related (LAR) gene in palmitate-induced insulin resistance in C2C12 cells. A stable C2C12 cell line was generated using LAR short hairpin RNA. The levels of LAR protein and phosphorylation of insulin receptor substrate-1 (IRS1) and Akt were detected by western blot analysis. 2-Deoxyglucose uptake was measured in LAR knockdown and control cells using d-[2-(3)H]glucose. LAR protein level was decreased by 65% in the stable cell line compared with the control cells. Palmitate (0.5 mM) significantly induced LAR mRNA (65%) and protein levels (40%) in myotubes compared with untreated cells. Palmitate significantly reduced insulin-stimulated glucose uptake in both the control and LAR knockdown cells by 33 and 51% respectively. However, LAR depletion improved insulin-stimulated glucose uptake in myotubes treated with palmitate. Furthermore, the inhibition of LAR prevented palmitate-induced decreases in phosphorylation of IRS1(Tyr632) and Akt(Ser473) in C2C12 cells. In conclusion, these results reveal that palmitate induces LAR expression in C2C12 cells. We also provided evidence that the inhibition of LAR attenuates palmitate-induced insulin resistance in myotubes.

Receptor type protein tyrosine phosphatases (RPTPs) - roles in signal transduction and human disease

Protein tyrosine phosphorylation is a fundamental regulatory mechanism controlling cell proliferation, differentiation, communication, and adhesion. Disruption of this key regulatory mechanism contributes to a variety of human diseases including cancer, diabetes, and auto-immune diseases. Net protein tyrosine phosphorylation is determined by the dynamic balance of the activity of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Mammals express many distinct PTKs and PTPs. Both of these families can be sub-divided into non-receptor and receptor subtypes. Receptor protein tyrosine kinases (RPTKs) comprise a large family of cell surface proteins that initiate intracellular tyrosine phosphorylation-dependent signal transduction in response to binding of extracellular ligands, such as growth factors and cytokines. Receptor-type protein tyrosine phosphatases (RPTPs) are enzymatic and functional counterparts of RPTKs. RPTPs are a family of integral cell surface proteins that possess intracellular PTP activity, and extracellular domains that have sequence homology to cell adhesion molecules. In comparison to extensively studied RPTKs, much less is known about RPTPs, especially regarding their substrate specificities, regulatory mechanisms, biological functions, and their roles in human diseases. Based on the structure of their extracellular domains, the RPTP family can be grouped into eight sub-families. This article will review one representative member from each RPTP sub-family.

PTPRF is disrupted in a patient with syndromic amastia

BACKGROUND

The presence of mammary glands distinguishes mammals from other organisms. Despite significant advances in defining the signaling pathways responsible for mammary gland development in mice, our understanding of human mammary gland development remains rudimentary. Here, we identified a woman with bilateral amastia, ectodermal dysplasia and unilateral renal agenesis. She was found to have a chromosomal balanced translocation, 46,XX,t(1;20)(p34.1;q13.13). In addition to characterization of her clinical and cytogenetic features, we successfully identified the interrupted gene and studied its consequences.

METHODS

Characterization of the breakpoints was performed by molecular cytogenetic techniques. The interrupted gene was further analyzed using quantitative real-time PCR and western blotting. Mutation analysis and high-density SNP array were carried out in order to find a pathogenic mutation. Allele segregations were obtained by haplotype analysis.

RESULTS

We enabled to identify its breakpoint on chromosome 1 interrupting the protein tyrosine receptor type F gene (PTPRF). While the patient's mother and sisters also harbored the translocated chromosome, their non-translocated chromosomes 1 were different from that of the patient. Although a definite pathogenic mutation on the paternal allele could not be identified, PTPRF's RNA and protein of the patient were significantly less than those of her unaffected family members.

CONCLUSIONS

Although ptprf has been shown to involve in murine mammary gland development, no evidence has incorporated PTPRF in human organ development. We, for the first time, demonstrated the possible association of PTPRF with syndromic amastia, making it a prime candidate to investigate for its spatial and temporal roles in human breast development.

Regulatory role of leukocyte-common-antigen-related molecule (LAR) in thymocyte differentiation

The strength of interaction between the antigenic peptide-loaded MHC (MHC/p) and the TCR determines T-cell fate in the thymus. A high avidity interaction between the TCR and the MHC/p induces apoptosis of self-reactive T cells (negative selection), whereas a moderate avidity interaction rescues thymocytes from apoptosis and permits further differentiation to mature T cells (positive selection). Leukocyte common antigen-related molecule (LAR), a receptor-like protein tyrosine phosphatase, is expressed on immature thymocytes, but its role in thymocyte differentiation has not yet been fully elucidated. We analyzed LAR-deficient mice and demonstrated that LAR deficiency affected the differentiation and expansion of immature thymocytes as well as positive and negative selection. Furthermore, LAR deficiency resulted in a lower Ca2+ response. The results indicate that LAR is an important modulator of TCR signaling that controls thymocyte differentiation.

Mammary involution and breast cancer risk: transgenic models and clinical studies

Postlactational involution is the process following weaning during which the mammary gland undergoes massive cell death and tissue remodeling as it returns to the pre-pregnant state. Lobular involution is the process by which the breast epithelial tissue is gradually lost with aging of the mammary gland. While postlactational involution and lobular involution are distinct processes, recent studies have indicated that both are related to breast cancer development. Experiments using a variety of rodent models, as well as observations in human populations, suggest that deregulation of postlactational involution may act to facilitate tumor formation. By contrast, new human studies show that completion of lobular involution protects against subsequent breast cancer incidence.

Maturation of ureter-bladder connection in mice is controlled by LAR family receptor protein tyrosine phosphatases

Congenital anomalies affecting the ureter-bladder junction are frequent in newborns and are often associated with other developmental defects. However, the molecular and morphological processes underlying these malformations are still poorly defined. In this study, we identified the leukocyte antigen-related (LAR) family protein tyrosine phosphatase, receptor type, S and F (Ptprs and Ptprf [also known as Lar], respectively), as crucially important for distal ureter maturation and craniofacial morphogenesis in the mouse. Embryos lacking both Ptprs and Ptprf displayed severe urogenital malformations, characterized by hydroureter and ureterocele, and craniofacial defects such as cleft palate, micrognathia, and exencephaly. The detailed analysis of distal ureter maturation, the process by which the ureter is displaced toward its final position in the bladder wall, leads us to propose a revised model of ureter maturation in normal embryos. This process was deficient in embryos lacking Ptprs and Ptprf as a result of a marked reduction in intrinsic programmed cell death, thereby causing urogenital system malformations. In cell culture, Ptprs bound and negatively regulated the phosphorylation and signaling of the Ret receptor tyrosine kinase, whereas Ptprs-induced apoptosis was inhibited by Ret expression. Together, these results suggest that ureter positioning is controlled by the opposing actions of Ret and LAR family phosphatases regulating apoptosis-mediated tissue morphogenesis.

Expression of the putative tumor suppressor gene PTPN13/PTPL1 is an independent prognostic marker for overall survival in breast cancer

Although it is well established that some protein tyrosine kinases have a prognostic value in breast cancer, the involvement of protein tyrosine phosphatases (PTPs) is poorly substantiated for breast tumors. Three of these enzymes (PTP-gamma, LAR, and PTPL1) are already known to be regulated by estrogens or their antagonists in human breast cancer cells. We used a real-time reverse transcriptase polymerase chain reaction method to test the expression levels of PTP-gamma, LAR and its neuronal isoform, and PTPL1 in a training set of RNA from 59 breast tumors. We sought correlations between levels of these molecular markers, current tumor markers, and survival. We then quantified the expression level of the selected phosphatase in 232 additional samples, resulting in a testing set of 291 breast tumor RNAs from patients with a median follow-up of 6.4 years. The Spearman nonparametric test revealed correlations between PTPL1 expression and differentiation markers. Cox univariate analysis of the overall survival studies demonstrated that PTPL1 is a prognostic factor [risk ratio (RR)=0.45], together with the progesterone receptor (PR) (RR=0.52) and node involvement (RR=1.58). In multivariate analyses, PTPL1 and PR retained their prognostic value (RRs of 0.48 and 0.55, respectively). This study demonstrates for the first time that PTPL1 expression level is an independent prognostic indicator of favorable outcome for patients with breast cancer. In conjunction with our mechanistic studies, this finding identifies PTPL1 as an important regulatory element of human breast tumor aggressiveness and sensitivity to treatments such as antiestrogens and antiaromatase.

Leukocyte antigen-related protein tyrosine phosphatase negatively regulates hydrogen peroxide-induced vascular smooth muscle cell apoptosis

Reactive oxygen species (ROS) have been implicated in vascular smooth muscle cell (VSMC) apoptosis, a hallmark of advanced atherosclerotic lesions. Transient oxidation and inactivation of protein-tyrosine phosphatases play a critical role in cellular response to ROS production. However, the function of leukocyte antigen-related (LAR) protein-tyrosine phosphatase in ROS signaling is not known. To determine the expression of LAR in ROS-induced apoptosis, we investigated hydrogen peroxide-induced cell death and signaling in aortic VSMCs from wild-type and LAR(-/-) mice. Histone-associated DNA fragmentation and caspase-3/7 activity were significantly enhanced, mitochondrial membrane integrity was compromised, and cell viability was significantly decreased following H(2)O(2) treatment in LAR(-/-) VSMCs compared with wild-type cells. Stronger and sustained increase in autophosphorylation and activity of Fyn, an Src family tyrosine kinase, was observed in LAR(-/-) cells compared with wild-type cells following H(2)O(2) treatment. LAR binds to activated Fyn in H(2)O(2)-treated VSMCs, and recombinant LAR dephosphorylates phosphorylated-Fyn in vitro. In addition, LAR deficiency enhanced H(2)O(2)-induced phosphorylation of Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and p38 mitogen-activated protein kinase (MAPK). PP2, a Fyn-specific inhibitor, blocked JAK2, STAT3, and p38 MAPK activation and significantly attenuated apoptosis induced by H(2)O(2). AG490, a JAK2-specific inhibitor, significantly attenuated H(2)O(2)-induced apoptosis, and blocked H(2)O(2)-induced activation of STAT3, but not p38 MAPK in both wild-type and LAR(-/-) VSMCs. Attenuation of Fyn expression by short hairpin RNA significantly decreased H(2)O(2)-induced downstream signaling and apoptosis in VSMCs. Together, these data indicate that LAR regulates Fyn/JAK2/STAT3 and Fyn/p38 MAPK pathways involved in ROS-induced apoptosis.

Restrictase free generation of targeting vectors for disruption of complex mouse genes

Molecular cloning of targeting vectors (TgVs) is a prerequisite procedure for gene disruption in embryonic stem cells. In cases where target genes display complex features (e.g., gene overlap, alternative exon usage), TgVs must mediate deletions with very high precision to prevent unwanted effects. This is often difficult to achieve by procedures using restriction endonucleases and DNA ligases. Therefore, to prepare TgVs for inactivation of two complex genes of immunological interest: PTPRF and NWC, we employed an alternative method, which involves engineering bacterial artificial chromosomes (BACs) by inducible, plasmid encoded "Red/ET recombinase" expression system. Here, we report rapid and efficient construction of PTPRF and NWC TgVs without using restriction endonucleases.

Inhibitor of growth 4 suppresses cell spreading and cell migration by interacting with a novel binding partner, liprin alpha1

Inhibitor of growth 4 (ING4) is a candidate tumor suppressor that plays a major role in gene regulation, cell cycle control, apoptosis, and angiogenesis. ING4 expression is down-regulated in glioblastoma cells and head and neck squamous cell carcinoma. Here, we identified liprin alpha1/PPFIA1, a cytoplasmic protein necessary for focal adhesion formation and axon guidance, as a novel interacting protein with ING4. ING4 and liprin alpha1 colocalized at lamellipodia in the vicinity of vinculin. Overexpressed ING4 suppressed cell spreading and cell migration. In contrast, overexpressed liprin alpha1 enhanced cell spreading and cell migration. Knockdown of endogenous ING4 with RNA interference induced cell motility, whereas knockdown of endogenous liprin alpha1 suppressed cell motility. ING4 also suppressed cell motility that was enhanced by liprin alpha1. However, ING4 did not further suppress cell motility when liprin alpha1 was suppressed with RNA interference, suggesting a functional and mechanistic interdependence between these proteins. In addition to its nuclear functions, cytoplasmic ING4 interacts with liprin alpha1 to regulate cell migration and, with its known antiangiogenic function, may prevent invasion and metastasis.

Cell surface nucleolin on developing muscle is a potential ligand for the axonal receptor protein tyrosine phosphatase-sigma

Reversible tyrosine phosphorylation, catalyzed by receptor tyrosine kinases and receptor tyrosine phosphatases, plays an essential part in cell signaling during axonal development. Receptor protein tyrosine phosphatase-sigma has been implicated in the growth, guidance and repair of retinal axons. This phosphatase has also been implicated in motor axon growth and innervation. Insect orthologs of receptor protein tyrosine phosphatase-sigma are also implicated in the recognition of muscle target cells. A potential extracellular ligand for vertebrate receptor protein tyrosine phosphatase-sigma has been previously localized in developing skeletal muscle. The identity of this muscle ligand is currently unknown, but it appears to be unrelated to the heparan sulfate ligands of receptor protein tyrosine phosphatase-sigma. In this study, we have used affinity chromatography and tandem MS to identify nucleolin as a binding partner for receptor protein tyrosine phosphatase-sigma in skeletal muscle tissue. Nucleolin, both from tissue lysates and in purified form, binds to receptor protein tyrosine phosphatase-sigma ectodomains. Its expression pattern also overlaps with that of the receptor protein tyrosine phosphatase-sigma-binding partner previously localized in muscle, and nucleolin can also be found in retinal basement membranes. We demonstrate that a significant amount of muscle-associated nucleolin is present on the cell surface of developing myotubes, and that two nucleolin-binding components, lactoferrin and the HB-19 peptide, can block the interaction of receptor protein tyrosine phosphatase-sigma ectodomains with muscle and retinal basement membranes in tissue sections. These data suggest that muscle cell surface-associated nucleolin represents at least part of the muscle binding site for axonal receptor protein tyrosine phosphatase-sigma and that nucleolin may also be a necessary component of basement membrane binding sites of receptor protein tyrosine phosphatase-sigma.

Tyrosine phosphatases epsilon and alpha perform specific and overlapping functions in regulation of voltage-gated potassium channels in Schwann cells

Tyrosine phosphatases (PTPs) epsilon and alpha are closely related and share several molecular functions, such as regulation of Src family kinases and voltage-gated potassium (Kv) channels. Functional interrelationships between PTPepsilon and PTPalpha and the mechanisms by which they regulate K+ channels and Src were analyzed in vivo in mice lacking either or both PTPs. Lack of either PTP increases Kv channel activity and phosphorylation in Schwann cells, indicating these PTPs inhibit Kv current amplitude in vivo. Open probability and unitary conductance of Kv channels are unchanged, suggesting an effect on channel number or organization. PTPalpha inhibits Kv channels more strongly than PTPepsilon; this correlates with constitutive association of PTPalpha with Kv2.1, driven by membranal localization of PTPalpha. PTPalpha, but not PTPepsilon, activates Src in sciatic nerve extracts, suggesting Src deregulation is not responsible exclusively for the observed phenotypes and highlighting an unexpected difference between both PTPs. Developmentally, sciatic nerve myelination is reduced transiently in mice lacking either PTP and more so in mice lacking both PTPs, suggesting both PTPs support myelination but are not fully redundant. We conclude that PTPepsilon and PTPalpha differ significantly in their regulation of Kv channels and Src in the system examined and that similarity between PTPs does not necessarily result in full functional redundancy in vivo.

Alpha-fetoprotein controls female fertility and prenatal development of the gonadotropin-releasing hormone pathway through an antiestrogenic action

It has been shown previously that female mice homozygous for an alpha-fetoprotein (AFP) null allele are sterile as a result of anovulation, probably due to a defect in the hypothalamic-pituitary axis. Here we show that these female mice exhibit specific anomalies in the expression of numerous genes in the pituitary, including genes involved in the gonadotropin-releasing hormone pathway, which are underexpressed. In the hypothalamus, the gonadotropin-releasing hormone gene, Gnrh1, was also found to be down-regulated. However, pituitary gene expression could be normalized and fertility could be rescued by blocking prenatal estrogen synthesis using an aromatase inhibitor. These results show that AFP protects the developing female brain from the adverse effects of prenatal estrogen exposure and clarify a long-running debate on the role of this fetal protein in brain sexual differentiation.

Downregulation of the LAR protein tyrosine phosphatase receptor is associated with increased dentate gyrus neurogenesis and an increased number of granule cell layer neurons

Growth factors stimulating neurogenesis act through protein tyrosine kinases which are counterbalanced by protein tyrosine phosphatases (PTPs); thus, downregulation of progenitor PTP function might provide a novel strategy for promoting neurogenesis. We tested the hypotheses that the leukocyte common antigen-related (LAR) PTP is present in adult dentate gyrus progenitors, and that its downregulation would promote neurogenesis. In adult mice, LAR immunostaining was present in Ki-67- and PCNA-positive subgranular zone cells. At 1 h post-BrdU administration, LAR-/- mice demonstrated an approximately 3-fold increase in BrdU- and PCNA-positive cells, indicating increased progenitor proliferation. At 1 day and 4 weeks following 6 days of BrdU administration, LAR-/- mice exhibited a significant increase in BrdU and NeuN colabeled cells consistent with increased neurogenesis. In association with increased neurogenesis in LAR-/- mice, stereological analysis revealed a significant 37% increase in the number of neurons present in the granule cell layer. In cultured progenitor clones derived from LAR+/+ mice, LAR immunostaining was present in PCNA- and BrdU-positive cells. Progenitor clones derived from adult LAR-/- hippocampus or LAR+/+ clones made LAR-deficient with LAR siRNA demonstrated increased proliferation and, under differentiation conditions, increased proportions of Tuj1- and MAP2-positive cells. These studies introduce LAR as the first PTP found to be expressed in dentate progenitors and point to inhibition of LAR as a potential strategy for promoting neurogenesis. These findings also provide a rare in vivo demonstration of an association between increased dentate neurogenesis and an expanded population of granule cell layer neurons.

Effects of LAR and PTP-BL phosphatase deficiency on adult mouse retinal cells activated by lens injury

Using intact and lens-lesioned wildtype, leucocyte common antigen-related phosphatase deficient (LARDeltaP) and protein tyrosine phosphatase (PTP)-BAS-like phosphatase deficient (PTP-BLDeltaP) mice, we have evaluated the role of LAR and PTP-BL in retinal ganglion cell survival and neuritogenesis, and survival of activated retinal glia in vitro. There were no differences in in vitro retinal ganglion cell neuritogenesis and survival, as well as in activated retinal glia survival between intact wildtype and intact LARDeltaP or PTP-BLDeltaP mutant mice. In wildtype, LARDeltaP, and PTP-BLDeltaP retinal cultures, pre-conditioning by lens injury significantly increased retinal ganglion cell neuritogenesis and activated retinal glia numbers. However, in retinal cultures from lens-lesioned LARDeltaP and PTP-BLDeltaP mice, significantly smaller percentages of retinal ganglion cells grew neurites compared to lens-lesioned wildtype cultures. Significantly increased numbers of retinal ganglion cells survived in retinal cultures from lens-lesioned LARDeltaP mice compared to lens-lesioned wildtypes. PTP-BL phosphatase deficiency did not affect retinal ganglion cell survival in retinal cultures from lens-lesioned mice, though activated retinal glia numbers were significantly reduced in cultures from lens-lesioned PTP-BLDeltaP mice compared to lens-lesioned wildtypes. In summary, a functional phenotype was found in LARDeltaP and PTP-BLDeltaP mice, that was only obvious in lens lesion-stimulated retinal cultures. These observations suggest that LAR enhances retinal ganglion cell neurite initiation whilst suppressing retinal ganglion cell survival, and that PTP-BL facilitates both retinal ganglion cell neurite initiation and survival of activated retinal glia.

Investigations of linker structure on the potency of a series of bidentate protein tyrosine phosphatase inhibitors

Protein tyrosine phosphatases (PTPases) and protein tyrosine kinase (PTKases) regulate the phosphorylation and dephosphorylation of tyrosine residues in proteins, events that are essential for a variety of cellular functions. PTPases such as PTP1B and the Yersinia PTPase play an important role in diseases including type II diabetes and bubonic plague. A library of 67 bidentate PTPase inhibitors that are based on the alpha-ketocarboxylic acid motif has been synthesized using parallel solution-phase methods. Two aryl alpha-ketocarboxylic acids were tethered to a variety of different diamine linkers through amide bonds. The compounds were assayed in crude form against the Yersinia PTPase, PTP1B, and TCPTP. Six compounds were selected for further evaluation, in purified form, against the Yersinia PTPase, PTP1B, TCPTP, LAR, and CD45. These compounds had IC50 values in the low micromolar range against the Yersinia PTPase, PTP1B, and TCPTP, showed good selectivity for PTP1B over LAR, and modest selectivity over CD45. The correlation between linker structure and inhibitor activity shows that aromatic groups in the linker can play an important role in determining binding affinity in this class of inhibitors.

Protein tyrosine phosphatases and breast cancer

Protein tyrosine phosphatases (PTPs) consist of a large family of related enzymes, including the group of classical PTPs with its two main subgroups, the transmembrane receptor-type (RPTPs) and the intracellular or non-transmembrane PTPs. Published data on the expression and function of a panel of these enzymes in normal and cancerous breast tissues are discussed in this review. While most studies, albeit on different enzymes, have tended to agree on the evidence for an increased PTP expression in breast cancer, any connection between PTP expression and the enzymes' role in cancer development and progression remains largely open to interpretation. Concomitant increases of protein tyrosine kinase (PTK) and PTP activities in many cancers further indicate that a complex dysregulation in the balance of tyrosine phosphorylation could be responsible for major alterations in various cellular processes controlling tissue homeostasis. In particular, any relationship between the expression of PTPs and their specific diverse roles in the regulation of cell growth and apoptosis in breast cancer needs to be addressed in major fundamental, preclinical and clinical studies.

Elf5 is essential for early embryogenesis and mammary gland development during pregnancy and lactation

Elf5 is an epithelial-specific ETS factor. Embryos with a null mutation in the Elf5 gene died before embryonic day 7.5, indicating that Elf5 is essential during mouse embryogenesis. Elf5 is also required for proliferation and differentiation of mouse mammary alveolar epithelial cells during pregnancy and lactation. The loss of one functional allele led to complete developmental arrest of the mammary gland in pregnant Elf5 heterozygous mice. A quantitative mRNA expression study and Western blot analysis revealed that decreased expression of Elf5 correlated with the downregulation of milk proteins in Elf5(+/-) mammary glands. Mammary gland transplants into Rag(-/-) mice demonstrated that Elf5(+/-) mammary alveolar buds failed to develop in an Elf5(+/+) mammary fat pad during pregnancy, demonstrating an epithelial cell autonomous defect. Elf5 expression was reduced in Prolactin receptor (Prlr) heterozygous mammary glands, which phenocopy Elf5(+/-) glands, suggesting that Elf5 and Prlr are in the same pathway. Our data demonstrate that Elf5 is essential for developmental processes in the embryo and in the mammary gland during pregnancy.

Mice lacking leukocyte common antigen-related (LAR) protein tyrosine phosphatase domains demonstrate spatial learning impairment in the two-trial water maze and hyperactivity in multiple behavioural tests

Leukocyte common antigen-related (LAR) protein is a cell adhesion molecule-like receptor-type protein tyrosine phosphatase. We previously reported that in LAR tyrosine phosphatase-deficient (LAR-Delta P) mice the number and size of basal forebrain cholinergic neurons as well as their innervation of the hippocampal area was reduced. With the hippocampus being implicated in behavioural activity aspects, including learning and memory processes, we assessed possible phenotypic consequences of LAR phosphatase deficiency using a battery of rodent behaviour tests. Motor function and co-ordination tests as well as spatial learning ability assays did not reveal any performance differences between wildtype and LAR-Delta P mice. A spatial learning impairment was found in the difficult variant of the Morris water maze. Exploration, nestbuilding and activity tests indicated that LAR-Delta P mice were more active than wildtype littermates. The observed hyperactivity in LAR-Delta P mice could not be explained by altered anxiety or curiosity levels, and was found to be persistent throughout the nocturnal period. In conclusion, behavioural testing of the LAR-Delta P mice revealed a spatial learning impairment and a significant increase in activity.

Functional significance of the LAR receptor protein tyrosine phosphatase family in development and diseases

The protein tyrosine phosphatases (PTPs) have emerged as critical players in diverse cellular functions. The focus of this review is the leukocyte common antigen-related (LAR) subfamily of receptor PTPs (RPTPs). This subfamily is composed of three vertebrate homologs, LAR, RPTP-sigma, and RPTP-delta, as well as few invertebrates orthologs such as Dlar. LAR-RPTPs have a predominant function in nervous system development that is conserved throughout evolution. Proteolytic cleavage of LAR-RPTP proproteins results in the noncovalent association of an extracellular domain resembling cell adhesion molecules and intracellular tandem PTPs domains, which is likely regulated via dimerization. Their receptor-like structures allow them to sense the extracellular environment and transduce signals intracellularly via their cytosolic PTP domains. Although many interacting partners of the LAR-RPTPs have been identified and suggest a role for the LAR-RPTPs in actin remodeling, very little is known about the mechanisms of action of RPTPs. LAR-RPTPs recently raised a lot of interest when they were shown to regulate neurite growth and nerve regeneration in transgenic animal models. In addition, LAR-RPTPs have also been implicated in metabolic regulation and cancer. This RPTP subfamily is likely to become important as drug targets in these various human pathologies, but further understanding of their complex signal transduction cascades will be required.Key words: protein tyrosine phosphatase, LAR, signal transduction, nervous system development.

Organogenesis of the exocrine gland

Morphogenesis of exocrine glands is a complex stepwise process of epithelial ingrowth, ductal elongation, ductal branching, and alveolar or acinar differentiation. Emerging from an increasing number of mouse gene knockout, dominant-negative, and antisense models is the identification of a remarkable collection of cell adhesion molecules, growth factors, and their receptors whose time-dependent contributions to glandular organogenesis are essential. Many have cryptically overlapping and interdependent but noncompensatory roles. Discoidin domain receptor 1 tyrosine kinase (DDR1) and the ErbB1 receptor of amphiregulin are, for example, required for ductal branching and elongation. Each is in turn dependent on the Wnt family of morphogenic factors for autophosphorylation or transactivation, respectively. Here we review the current cast of exocrine glandular morphogens, as a foundation for a global or systems biology appreciation of the interweaving signaling pathways that underlie mammalian glandular morphogenesis.

Insulin signaling and glucose homeostasis in mice lacking protein tyrosine phosphatase α

Studies in cultured cells have implicated protein tyrosine phosphatase alpha (PTPalpha) as a potential regulator of insulin signaling. The physiological role of PTPalpha in insulin action was investigated using gene-targeted mice deficient in PTPalpha. PTPalpha-null animals had normal body weights and circulating levels of glucose and insulin in random fed and fasted states. In glucose and insulin tolerance tests, their efficiency of blood glucose clearance was comparable to wild-type mice. Kinetics and extents of insulin-stimulated insulin receptor and IRS-1 tyrosine phosphorylation were similar in wild-type and PTPalpha(-/-) liver, muscle, and adipose tissue. However, the association of IRS-1 and PI 3-K was altered in PTPalpha(-/-) liver, with increased insulin-independent and reduced insulin-stimulated association compared to wild-type samples. This did not affect activation of the downstream signaling effector Akt. Our data indicate that PTPalpha is not a negative regulator of insulin signaling and does not perform an essential role in mediating the physiological action of insulin.

Genetic Manipulation of Mammary Gland Development and Lactation

The mammalian genome is believed to contain some 30,000 to 40,000 different genes. Of these an estimated 42% have no known function. Genetically engineered mouse models (GEMM) have been a powerful tool available for determining gene function in vivo. In the mammary gland, a variety of genetic engineering approaches have been applied successfully to understanding the importance of specific gene products to mammary gland development and lactation. Our own laboratory has applied genetically engineered mice to facilitate understanding of the regulation of mammary gland development and lactation by insulin-like growth factors (IGF) and by the transcription factor, upstream stimulatory factor (USF-2). Our studies on transgenic mice that overexpress IGF-I have demonstrated the importance of IGF-dependent signaling pathways to maintenance of mammary epithelial cells during the declining phase of lactation. Our analysis of early developmental processes in mammary tissue from mice that carry a targeted mutation in the IGF-I receptor gene suggests that IGF-dependent stimulation of cell cycle progression is more important to early mammary gland development than potential antiapoptotic effects. Lastly, our studies on mice that carry a targeted mutation of the Usf2 gene have demonstrated that this gene is necessary for normal lactation and have highlighted the importance of this gene to the maintenance of protein synthesis. These studies, as well as studies of others, have highlighted both the strengths and limitations inherent in the use of GEMM. Limitations serve as the driving force behind development of new experimental strategies and genetic engineering schemes that will allow for a full understanding of gene function within the mammary gland.

Mutational analysis of the cytoplasmic domain of beta1,4-galactosyltransferase I: influence of phosphorylation on cell surface expression

Beta1,4-galactosyltransferase I (GalT I) exists in two subcellular compartments where it performs two distinct functions. The majority of GalT I is localized in the Golgi complex where it participates in glycoprotein biosynthesis; however, a small portion of GalT I is expressed on the cell surface where it functions as a matrix receptor by binding terminal N-acetylglucosamine residues on extracellular glycoside ligands. The GalT I polypeptide occurs in two alternate forms that differ only in the length of their cytoplasmic domains. It is thought that the longer cytoplasmic domain is responsible for GalT I function as a cell surface receptor because of its ability to associate with the detergent-insoluble cytoskeleton. In this study, we demonstrate that the long GalT I cytoplasmic and transmembrane domains are capable of targeting a reporter protein to the plasma membrane, whereas the short cytoplasmic and transmembrane domains do not have this property. The surface-localized GalT I reporter protein partitions with the detergent-insoluble pool, a portion of which co-fractionates with caveolin-containing lipid rafts. Site-directed mutagenesis of the cytoplasmic domain identified a requirement for serine and threonine residues for cell surface expression and function. Replacing either the serine or threonine with aspartic acid reduces surface expression and function, whereas substitution with neutral alanine has no effect on surface expression or function. These results suggest that phosphorylation negatively regulates GalT I function as a surface receptor. Consistent with this, phosphorylation of the endogenous, full-length GalT I inhibits its stable expression on the cell surface. Thus, the 13 amino acid extension unique to the long GalT I isoform is required for GalT I expression on the cell surface, the function of which is regulated by phosphorylation.

The Cascade Hypothesis of Keratoconus

Keratoconus, a non-inflammatory thinning of the cornea, is a leading indication for corneal transplantation. For its causation, we propose a "Cascade Hypothesis" stating that keratoconus corneas have abnormal or defective enzymes in the lipid peroxidation and/or nitric oxide pathways leading to oxidative damage. The accumulation of oxidative, cytotoxic by-products causes an alteration of various corneal proteins, triggering a cascade of events, (i.e. apoptosis, altered signaling pathways, increased enzyme activities, fibrosis). This hypothesis is supported by biochemical, immunohistochemical and molecular data presented in this review. Based upon this evidence, one can speculate that keratoconus patients should minimize their exposure to oxidative stress. Protective steps should include wearing ultraviolet (UV) protection (in the contact lenses and/or sunglasses), minimizing the mechanical trauma (eye rubbing, poorly fit contact lenses) and keeping eyes comfortable with artificial tears, non-steroidal anti-inflammatory drugs and/or allergy medications.

Phosphatases in cell–matrix adhesion and migration

Many proteins that have been implicated in cell-matrix adhesion and cell migration are phosphorylated, which regulates their folding, enzymatic activities and protein-protein interactions. Although modulation of cell motility by kinases is well known, increasing evidence confirms that phosphatases are essential at each stage of the migration process. Phosphatases can control the formation and maintenance of the actin cytoskeleton, regulate small GTPase molecular switches, and modulate the dynamics of matrix-adhesion interaction, actin contraction, rear release and migratory directionality.