Polymersomes: a new multi-functional tool for cancer diagnosis and therapy

Nanoparticles are being developed as delivery vehicles for therapeutic pharmaceuticals and contrast imaging agents. Polymersomes (mesoscopic polymer vesicles) possess a number of attractive biomaterial properties that make them ideal for these applications. Synthetic control over block copolymer chemistry enables tunable design of polymersome material properties. The polymersome architecture, with its large hydrophilic reservoir and its thick hydrophobic lamellar membrane, provides significant storage capacity for both water soluble and insoluble substances (such as drugs and imaging probes). Further, the brush-like architecture of the polymersome outer shell can potentially increase biocompatibility and blood circulation times. A further recent advance is the development of multi-functional polymersomes that carry pharmaceuticals and imaging agents simultaneously. The ability to conjugate biologically active ligands to the brush surface provides a further means for targeted therapy and imaging. Hence, polymersomes hold enormous potential as nanostructured biomaterials for future in vivo drug delivery and diagnostic imaging applications.

Special regulatory T-cell review: FOXP3 biochemistry in regulatory T cells--how diverse signals regulate suppression

FOXP3 is an acetylated and phosphorylated protein active in human regulatory T cells and forms oligomers which then associate with an even larger molecular complex. FOXP3 actively regulates transcription by recruiting enzymatic co-repressors and/or co-activators. FOXP3 complex ensembles are dynamically regulated by physiological stimuli such as T-cell receptor, IL-2 and proinflammation cytokine signals. Understanding the post-translational modifications of FOXP3 regulated by diverse signals and the biochemistry and structural chemistry of enzymatic proteins in the FOXP3 complex is critical for therapeutically modulating regulatory T cell function.

Differential binding patterns of monoclonal antibody 2C4 to the ErbB3-p185her2/neu and the EGFR-p185her2/neu complexes

2C4 (Pertuzumab, Omnitarg) is a monoclonal antibody targeting p185(her2/neu), which is overexpressed in 30% of invasive breast cancer. 2C4 is currently in phase II clinical trials for several types of cancers. This antibody has been reported to disrupt the association between p185(her2/neu) and ErbB3. In our studies of epidermal growth factor receptor (EGFR)-p185(her2/neu) heterodimerization, we noted that 2C4 formed associations with the EGFR-p185(her2/neu) receptor complex. Our data argue against 2C4 as a universal heterodimerization blocker for p185(her2/neu), but indicate that cocktails of monoclonal antibodies binding distinct interaction surfaces of p185(her2/neu) will emerge as the most potent targeted therapy.

Smad3 and NFAT cooperate to induce Foxp3 expression through its enhancer

The transcription factor Foxp3 is involved in the differentiation, function and survival of CD4+CD25+ regulatory T (T(reg)) cells. Details of the mechanism underlying the induction of Foxp3 expression remain unknown, because studies of the transcriptional regulation of the Foxp3 gene are limited by the small number of T(reg) cells in mononuclear cell populations. Here we have generated a model system for analyzing Foxp3 induction and, by using this system with primary T cells, we have identified an enhancer element in this gene. The transcription factors Smad3 and NFAT are required for activity of this Foxp3 enhancer, and both factors are essential for histone acetylation in the enhancer region and induction of Foxp3. These biochemical properties that define Foxp3 expression explain many of the effects of transforming growth factor-beta on the function of Foxp3+ T(reg) cells.

Deacetylase inhibition promotes the generation and function of regulatory T cells

Histone/protein deacetylases (HDACs) regulate chromatin remodeling and gene expression as well as the functions of more than 50 transcription factors and nonhistone proteins. We found that administration of an HDAC inhibitor (HDACi) in vivo increased Foxp3 gene expression, as well as the production and suppressive function of regulatory T cells (T(reg) cells). Although T(reg) cells express multiple HDACs, HDAC9 proved particularly important in regulating Foxp3-dependent suppression. Optimal T(reg) function required acetylation of several lysines in the forkhead domain of Foxp3, and Foxp3 acetylation enhanced binding of Foxp3 to the Il2 promoter and suppressed endogenous IL-2 production. HDACi therapy in vivo enhanced T(reg)-mediated suppression of homeostatic proliferation, decreased inflammatory bowel disease through T(reg)-dependent effects, and, in conjunction with a short course of low-dose rapamycin, induced permanent, T(reg)-dependent cardiac and islet allograft survival and donor-specific allograft tolerance. Our data show that use of HDACi allows the beneficial pharmacologic enhancement of both the numbers and suppressive function of Foxp3(+) T(reg) cells.

Histone deacetylase inhibitors and transplantation

Simply detecting the presence or absence of Foxp3, a transcription factor characteristic of naturally occurring CD4+ CD25+ regulatory T cells (Tregs), now appears of minimal value in predicting the outcome of immunologic responses, since dividing human CD4+ effector T cells can induce Foxp3 without attaining repressive functions, and additional molecular interactions, as well epigenetic events, affect Foxp3-dependent Treg functions in humans and mice. Experimentally, in vivo and in vitro studies show histone deacetylase inhibitors (HDACi) can enhance the numbers and suppressive function of regulatory T cells (Tregs) by promoting Foxp3+ cell production, enhancing chromatin remodeling within Tregs, and inducing acetylation of Foxp3 protein itself. Human studies consistent with a role for HDACi in controlling Fox3-dependent Treg functions are also available. We review these molecular interactions and how they may be exploited therapeutically to enhance Treg-dependent functions, including post-transplantation.

CD147 immunoglobulin superfamily receptor function and role in pathology

The immunoglobulin superfamily member CD147 plays an important role in fetal, neuronal, lymphocyte and extracellular matrix development. Here we review the current understanding of CD147 expression and protein interactions with regard to CD147 function and its role in pathologic conditions including heart disease, Alzheimer's disease, stroke and cancer. A model linking hypoxic conditions found within the tumor microenvironment to upregulation of CD147 expression and tumor progression is introduced.

Biochemistry and therapeutic implications of mechanisms involved in FOXP3 activity in immune suppression

While mutations in human FOXP3 predispose individuals to autoimmune conditions, it is unclear how the mutant protein fails to function as a transcriptional regulator. There is also limited detail of how FOXP3 itself interacts with the transcriptional machinery and which components of the FOXP3 ensembles exert phenotypic changes to render cells able to mediate suppression. Increasing evidence indicates that the level and duration of FOXP3 expression plays a crucial role in the development and function of natural regulatory T cells (Tregs). Our studies focus on the post-translational modification of the FOXP3 protein, and how the FOXP3 complex ensemble, containing histone modification and chromatin-remodeling enzymes, defines its functional role in regulatory T cells. Understanding the molecular mechanisms underlying FOXP3 activity will provide therapeutic implications for transplantation, allergy, autoimmune disease and cancer.

ErbB receptors: from oncogenes to targeted cancer therapies

Understanding the genetic origin of cancer at the molecular level has facilitated the development of novel targeted therapies. Aberrant activation of the ErbB family of receptors is implicated in many human cancers and is already the target of several anticancer therapeutics. The use of mAbs specific for the extracellular domain of ErbB receptors was the first implementation of rational targeted therapy. The cytoplasmic tyrosine kinase domain is also a preferred target for small compounds that inhibit the kinase activity of these receptors. However, current therapy has not yet been optimized, allowing for opportunities for optimization of the next generation of targeted therapy, particularly with regards to inhibiting heteromeric ErbB family receptor complexes.

FOXP3 is a homo-oligomer and a component of a supramolecular regulatory complex disabled in the human XLAAD/IPEX autoimmune disease

We have found that FOXP3 is an oligomeric component of a large supramolecular complex. Certain FOXP3 mutants with single amino acid deletions in the leucine zipper domain of FOXP3 are associated with the X-linked autoimmunity-allergic dysregulation (XLAAD) and immunodysregulation, polyendocrinopathy and enteropathy, X-linked (IPEX) syndrome in humans. We report that the single amino acid deletion found in human XLAAD/IPEX patients within the leucine zipper domain of FOXP3 does not disrupt its ability to join the larger protein complex, but eliminates FOXP3 homo-oligomerization as well as heteromerization with FOXP1. We found that the zinc finger-leucine zipper domain region of FOXP3 is sufficient to mediate both homodimerization and homotetramerization. However, the same domain region from XLAAD/IPEX FOXP3 containing an E251 deletion prevents oligomerizaton and the protein remains monomeric. We also found that wild-type FOXP3 directly binds to the human IL-2 promoter, but the E251 deletion in FOXP3 in XLAAD/IPEX patient's T cells disrupts its association with the IL-2 promoter in vivo and in vitro, and limits repression of IL-2 transcription after T-cell activation. Our results suggest that compromising FOXP3 homo-oligomerization and hetero-oligomerization with the FOXP1 protein impairs DNA-binding properties leading to distinct biochemical phenotypes in humans with the XLAAD/IPEX autoimmune syndrome. This study explains some features of the pathogenesis of a disease syndrome that arises as a consequence of specific assembly failure of a transcriptional repressor due to certain mutations within the FOXP3 leucine zipper.

FOXP3 actively represses transcription by recruiting the HAT/HDAC complex

The Forkhead box protein P3 (FOXP3) is a master cell lineage modulator in CD4(+)CD25(+) natural regulatory T cell (Treg) development. The Treg set of cells, also called T suppressor cells, play an essential role in natural Treg-mediated suppression of various types of immune cells. Suppression can be manifest by a cell-cell contact set of events, and recent evidence also supports soluble mediators. FOXP3 was previous identified as a passive transcriptional repressor which associates with nuclear factor of activated T-cells, cytoplasmic, and calcineurin-dependent 2 (NFATc2) as well as several other transcriptional factors including nuclear factor kappa-B (NFkappaB) and acute myeloid leukemia 1(AML1)/runt-related transcription factor 1(RUNX1). We found FOXP3 could actively repress transcription by recruiting distinct histone acetyltransferases and histone deacetylases to function as a co-repressor complex. The identification of enzymatic factors operative as essential participants in FOXP3-mediated transcriptional repression provides a practical basis for therapeutically modulating the activity of FOXP3 in immune suppression. Here we briefly summarize recent progress in our understanding of the biochemistry of FOXP3-mediated transcriptional regulation.

Gefitinib-sensitive EGFR lacking residues 746-750 exhibits hypophosphorylation at tyrosine residue 1045, hypoubiquitination, and impaired endocytosis

Gefitinib-sensitive nonsmall cell lung cancers (NSCLC) are characterized by somatic mutations in the kinase domain of epidermal growth factor receptor (EGFR). The mutant EGFR forms are reported to mediate characteristic signal transduction pathways that are different from those mediated by the wild-type EGFR and are involved in transformation in vivo. We have examined signal transduction pathways initiated from a frequently identified gefitinib-sensitizing mutant EGFR lacking residues 746-750 by employing a mouse fibroblast cell line that is free of endogenous EGFR and transiently transfected COS-7 cells. Upon EGF stimulation, the deletion-mutant EGFR mediated prolonged downstream signals. The analysis of the phosphotyrosine patterns of the receptor revealed that the deletion-mutant EGFR lacked phosphorylation at tyrosine residue 1045, which is the major binding site of Cbl. The EGF-induced endocytosis of the deletion-mutant EGFR was impaired. The ubiquitination and downregulation of the deletion-mutant EGFR were also reduced. On the other hand, another mutant, EGFR, possessing a L858R substitution, exhibited phosphorylation at 1045 and its downstream signalings were not prolonged. These data suggest that the signal transduction pathways initiated from these mutant forms are different, and that impaired endocytosis might be responsible for the prolonged signals mediated by the deletion-mutant EGFR.

FOXP3 is a homo-oligomer, and it interactions with histone acetyltransferase and class II histone deacetylases are required for repression (88.30)

We have found that FOXP3 is an oligomeric component of a large supramolecular complex. The Zinc-Leuzip region of FOXP3 is sufficient to mediate its homotetramerization. Wild type FOXP3 directly binds to the human IL-2 promoter, but the E251 deletion in FOXP3 in XLAAD/IPEX patient’s T cells disrupts its homo-oligomerization, heteromerization with FOXP1, its association with the IL-2 promoter, and limits repression of IL-2 transcription after T cell activation. Additionally we report that transcriptional repression by FOXP3 involves a histone acetylase-deacetylase complex that includes TIP60 and HDAC7 and HDAC9. FOXP3 can be acetylated, and TIP60 promotes FOXP3 acetylation in vivo. Knockdown of endogenous TIP60 relieved FOXP3-mediated transcriptional repression. A minimum FOXP3 ensemble containing native TIP60 and HDAC7 is necessary for IL-2 production regulation in T cells. Moreover, FOXP3 association with HDAC9 is antagonized by T cell stimulation, and can be restored by the Trichostatin A indicating a complex dynamic aspect of T suppressor cell regulation. These findings identify a novel complex based mechanism by which FOXP3 actively mediates transcriptional repression.

FOXP3 interactions with histone acetyltransferase and class II histone deacetylases are required for repression

The forkhead family protein FOXP3 acts as a repressor of transcription and is both an essential and sufficient regulator of the development and function of regulatory T cells. The molecular mechanism by which FOXP3-mediated transcriptional repression occurs remains unclear. Here, we report that transcriptional repression by FOXP3 involves a histone acetyltransferase-deacetylase complex that includes histone acetyltransferase TIP60 (Tat-interactive protein, 60 kDa) and class II histone deacetylases HDAC7 and HDAC9. The N-terminal 106-190 aa of FOXP3 are required for TIP60-FOXP3, HDAC7-FOXP3 association, as well as for the transcriptional repression of FOXP3 via its forkhead domain. FOXP3 can be acetylated in primary human regulatory T cells, and TIP60 promotes FOXP3 acetylation in vivo. Overexpression of TIP60 but not its histone acetyltransferase-deficient mutant promotes, whereas knockdown of endogenous TIP60 relieved, FOXP3-mediated transcriptional repression. A minimum FOXP3 ensemble containing native TIP60 and HDAC7 is necessary for IL-2 production regulation in T cells. Moreover, FOXP3 association with HDAC9 is antagonized by T cell stimulation and can be restored by the protein deacetylation inhibitor trichostatin A, indicating a complex dynamic aspect of T suppressor cell regulation. These findings identify a previously uncharacterized complex-based mechanism by which FOXP3 actively mediates transcriptional repression.

Targeted antireceptor therapy with monoclonal antibodies leads to the formation of inactivated tetrameric forms of ErbB receptors

mAbs capable of disabling heterodimeric kinase complexes of the epidermal growth factor receptor (EGFR) and human EGFR type 2/neu have therapeutic relevance to various human cancers. In this study, we demonstrate that in addition to the dimer, EGFR and human EGFR type 2 can associate as homo- and heterotetramers. EGF-induced phosphorylation of the tetramers was significantly lower than that of the dimers, indicating that the tetrameric receptor complexes have impaired signaling activity. Targeting v-erb-b2 erythroblastic leukemia viral oncogene homolog (erbB) receptors with mAbs promoted erbB tetrameric assembly, suggesting that a component of the antitumor activity may be mediated by the ability of Abs to shift the equilibrium from active dimeric to impaired tetrameric receptor complex states. This study suggests a novel therapeutic approach to disable signaling of erbB and potentially other receptors in tumors by biologic agents capable of inducing receptor tetramerization.

Characterization of the structures involved in localization of the SUN proteins to the nuclear envelope and the centrosome

The nuclear envelope forms a selective barrier that separates the cytoplasm from the nucleus. During mitosis the nuclear envelope breaks down so that the microtubule network can form contacts with the kinetochore and guide chromosome segregation. Previous studies have suggested a model in which the centrosome and the microtubule network may play a role in nuclear envelope breakdown through as yet unidentified interactions with proteins localized to the nuclear envelope. In the current study we characterized a nuclear envelope protein SUN2 and identified a substructure involved in its localization to the nuclear envelope. We found that a structurally related protein, SUN1, may be localized to the nuclear envelope through a different mechanism. Furthermore, the SUN2 protein can form different assemblies, including homodimers and heterodimers with SUN1. Finally, we provide evidence indicating that SUN1 and SUN2 may form a physical interaction between the nuclear envelope and the centrosome.

The extracellular domain of p185(c-neu) induces density-dependent inhibition of cell growth in malignant mesothelioma cells and reduces growth of mesothelioma in vivo

EGFR is involved in the density-dependent inhibition of cell growth, while coexpression of EGFR with erbB2 can render normal cells transformed. In this study, we have examined the effect of a species of p185 that contains the transmembrane domain and the extracellular domain of p185(c-neu), on growth properties of a human malignant mesothelioma cell line that coexpresses EGFR and erbB2. The ectodomain form of p185(c-neu) enhanced density-dependent inhibition of cell growth and we found that p21 induction appeared to be responsible for this inhibitory effect. Previously, the extracellular domain species was shown to suppress the transforming abilities of EGFR and p185(c-neu/erbB2) in a dominant-negative manner. The ability of this subdomain to affect tumor growth is significant, as it reduced in vivo tumor growth. Unexpectedly, we found that the domain did not abrogate all of EGFR functions. We noted that EGFR-induced density-dependent inhibition of cell growth was retained. Tyrosine kinase inhibitors of EGFR did not cause density-dependent inhibition of cell growth of malignant mesothelioma cells. Therefore, simultaneously inhibiting the malignant phenotype and inducing density-dependent inhibition of cell growth in malignant mesothelioma cells by the extracellular domain of p185(c-neu) may represent an important therapeutic advance.

Test for detection of disease-associated prion aggregate in the blood of infected but asymptomatic animals

We have developed a sensitive in vitro assay for detecting disease-associated prion aggregates by combining an aggregation-specific enzyme-linked immunosorbent assay (AS-ELISA) with the fluorescent amplification catalyzed by T7 RNA polymerase technique (FACTT). The new assay, named aggregation-specific FACTT (AS-FACTT), is much more sensitive than AS-ELISA and could detect prion aggregates in the brain of mice as early as 7 days after an intraperitoneal inoculation of PrP(Sc). However, AS-FACTT was still unable to detect prion aggregates in blood of infected mice. To further improve the detection limit of AS-FACTT, we added an additional prion amplification step (Am) and developed a third-generation assay, termed Am-A-FACTT. Am-A-FACTT has 100% sensitivity and specificity in detecting disease-associated prion aggregates in blood of infected mice at late but still asymptomatic stages of disease. At a very early stage, Am-A-FACTT had a sensitivity of 50% and a specificity of 100%. Most importantly, Am-A-FACTT also detects prion aggregates in blood of mule deer infected with the agent causing a naturally occurring prion disease, chronic wasting disease. Application of this assay to cattle, sheep, and humans could safeguard food supplies and prevent human contagion.

DIPA, which can localize to the centrosome, associates with p78/MCRS1/MSP58 and acts as a repressor of gene transcription

DIPA (delta-interacting protein A) was initially identified as a protein that associates with the hepatitis delta antigen. In this study, we found that DIPA can associate with p78/MCRS/MSP58, a Forkhead-associated domain containing protein implicated in malignant transformation as well as in regulation of gene transcription and translation. We analyzed the interaction between DIPA and p78 by co-immunoprecipitation and identified the structural regions involved in the interaction. Consistent with the physical interaction, we found that DIPA is predominant co-localized with p78 to the nucleus. In addition, a fraction of DIPA can be detected on the centrosome. Furthermore, we demonstrate that DIPA can act as a repressor of gene transcription, an activity that appears to be enhanced by p78. Taken together, our results revealed a novel protein complex that plays a role in regulation of gene expression and cell proliferation. We propose that dysfunction of DIPA may contribute to malignant transformation by affecting the functions of p78.

FOXP3 ensembles in T-cell regulation

Our recent studies have identified dynamic protein ensembles containing forkhead box protein 3 (FOXP3) that provide insight into the molecular complexity of suppressor T-cell activities, and it is our goal to determine how these ensembles regulate FOXP3's transcriptional activity in vivo. In this review, we summarize our current understanding of how FOXP3 expression is induced and how FOXP3 functions in vivo as a transcriptional regulator by assembling a multisubunit complex involved in histone modification as well as chromatin remodeling.

AHNP-streptavidin: a tetrameric bacterially produced antibody surrogate fusion protein against p185her2/neu

The anti-p185(her2/neu) peptidomimetic (AHNP) is a small exo-cyclic peptide derived from the anti-p185(her2/neu) rhumAb 4D5 (h4D5). AHNP mimics many but not all of the antitumor characteristics exhibited by h4D5. However, the pharmacokinetic profiles of AHNP are less than optimal for therapeutic or diagnostic purposes. To improve the binding affinity to p185(her2/neu) and the antitumor efficacy, we have engineered a fusion protein containing AHNP and a nonimmunoglobulin protein scaffold, streptavidin (SA). The recombinant protein, AHNP-SA (ASA) bound to p185(her2/neu) with high affinity, inhibited the proliferation of p185(her2/neu)-overexpressing cells, and reduced tumor growth induced by p185(her2/neu)-transformed cells. These data suggest that the bacterially produced tetrameric ASA can be used as an antibody-surrogate molecule. This class of molecule will play a role in the diagnosis and treatment of p185(her2/neu)-related tumors. Our studies establish a general principle by which a small biologically active synthetic exo-cyclic peptide can be engineered to enhance functional aspects by structured oligomerization and can be produced recombinantly using bacterial expression.

Centrosomal proteins Nde1 and Su48 form a complex regulated by phosphorylation

The centrosome modulates spindle formation and plays a critical role in guiding proper segregation of chromosomes during cell division. Centrosome aberrations, frequently seen in human tumors, may cause abnormal chromosome segregation and contribute to malignant transformation. To explore the components of the centrosomes, we previously identified a novel centrosomal protein called Su48. To further characterize the Su48-containing protein ensemble in the centrosome, we performed yeast two-hybrid screens and isolated a number of Su48-interacting molecules, including the centrosomal protein Nde1. Here, we demonstrate that Su48 can associate with Nde1. Moreover, we found that Nde1 is subjected to phosphorylation in vivo. In particular, we identified six putative Cdc2 phosphorylation sites in Nde1 and found that alteration of these sites diminishes phosphorylation by Cdc2 in vitro and affects the stability of Su48-Nde1 interactions and the centrosomal localization of Nde1. Ablation of Nde1 by gene specific small interfering RNA causes mitotic delay and cell death, coupled with a modest decrease in the incidence of the cells that harbor excessive centrosomes. Collectively, our findings indicate that Nde1 can form a protein complex with Su48 in the centrosome and plays an important role for successful mitosis.

Characterization of Su48, a centrosome protein essential for cell division

The centrosome functions as the major microtubule-organizing center and plays a vital role in guiding chromosome segregation during mitosis. Centrosome abnormalities are frequently seen in a variety of cancers, suggesting that dysfunction of this organelle may contribute to malignant transformation. In our efforts to identify the protein components of the centrosome and to understand the structure features involved in the assembly and functions of this organelle, we cloned and characterized a centrosome-associated protein called Su48. We found that a coiled coil-containing subdomain of Su48 was both sufficient and required for its centrosome localization. In addition, this structure also modulates Su48 dimerization. Moreover, ectopic expression of Su48 causes abnormal mitosis, and a mutant form of Su48 disrupts the localization of gamma-tubulin to the centrosome. Finally, by microinjection of an anti-Su48 antibody, we found that disruption of normal Su48 functions leads to mitotic failure, possibly due to centrosome defects or incomplete cytokinesis. Thus, Su48 represents a previously unrecognized centrosome protein that is essential for cell division. We speculate that Su48 abnormalities may cause aberrant chromosome segregation and may contribute to aneuploidy and malignant transformation.

The Gefitinib-Sensitizing Mutant Epidermal Growth Factor Receptor Enables Transformation of a Mouse Fibroblast Cell Line

A specific inhibitor of the Epidermal Growth Factor Receptor (EGFR), Gefitinib, displays significant antitumor effects against non-small cell lung cancers (NSCLC) that express EGFR with mutations in their tyrosine kinase domain. Although previous reports have already demonstrated that oncogenic transformation can be induced by some mutant EGFR forms, the precise differences between mutant and wild-type EGFR in terms of mechanisms of transformation have not been fully elucidated. We show here that a murine fibroblast cell line, NR6 becomes transformed by an expression level of the mutant EGFR form lacking E746-A750 that is far less than that needed with transfected wild-type EGFR. However, the mutant EGFR was unable to transform NR6 in a ligand-independent manner, as was seen with the wild-type EGFR. The consequent biological features after transformation, including DNA synthesis or cell cycle progression and biochemical characteristics such as MAPK activation mediated by the mutant EGFR are comparable and equivalent to those mediated by wild-type EGFR. These data suggest that the mutant EGFR possesses greater ligand-dependent transformation when compared with wild-type EGFR, although the exact mechanisms to account for this characteristic remain to be defined.