Recent advances in orally administered cell-specific nanotherapeutics for inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic relapsing disease in gastrointestinal tract. Conventional medications lack the efficacy to offer complete remission in IBD therapy, and usually associate with serious side effects. Recent studies indicated that nanoparticle-based nanotherapeutics may offer precise and safe alternative to conventional medications via enhanced targeting, sustained drug release, and decreased adverse effects. Here, we reviewed orally cell-specific nanotherapeutics developed in recent years. In addition, the various obstacles for oral drug delivery are also reviewed in this manuscript. Orally administrated cell-specific nanotherapeutics is expected to become a novel therapeutic approach for IBD treatment.

Select membrane proteins modulate MNV-1 infection of macrophages and dendritic cells in a cell type-specific manner.

Noroviruses cause gastroenteritis in humans and other animals, are shed in the feces, and spread through the fecal-oral route. Host cellular expression of attachment and entry receptors for noroviruses is thought to be a key determinant of cell tropism and the strict species-specificity. However, to date, only carbohydrates have been identified as attachment receptors for noroviruses. Thus, we investigated whether host cellular proteins play a role during the early steps of norovirus infection. We used murine norovirus (MNV) as a representative norovirus, since MNV grows well in tissue culture and is a frequently used model to study basic aspects of norovirus biology. Virus overlay protein binding assay followed by tandem mass spectrometry analysis was performed in two permissive cell lines, RAW264.7 (murine macrophages) and SRDC (murine dendritic cells) to identify four cellular membrane proteins as candidates. Loss-of-function studies revealed that CD36 and CD44 promoted MNV-1 binding to primary dendritic cells, while CD98 heavy chain (CD98) and transferrin receptor 1 (TfRc) facilitated MNV-1 binding to RAW 264.7 cells. Furthermore, the VP1 protruding domain of MNV-1 interacted directly with the extracellular domains of recombinant murine CD36, CD98 and TfRc by ELISA. Additionally, MNV-1 infection of RAW 264.7 cells was enhanced by soluble rCD98 extracellular domain. These studies demonstrate that multiple membrane proteins can promote efficient MNV-1 infection in a cell type-specific manner. Future studies are needed to determine the molecular mechanisms by which each of these proteins affect the MNV-1 infectious cycle.

An ancestral host defence peptide within human ß-defensin 3 recapitulates the antibacterial and antiviral activity of the full-length molecule.

Host defence peptides (HDPs) are critical components of innate immunity. Despite their diversity, they share common features including a structural signature, designated "γ-core motif". We reasoned that for each HDPs evolved from an ancestral γ-core, the latter should be the evolutionary starting point of the molecule, i.e. it should represent a structural scaffold for the modular construction of the full-length molecule, and possess biological properties. We explored the γ-core of human ß-defensin 3 (HBD3) and found that it: (a) is the folding nucleus of HBD3; (b) folds rapidly and is stable in human serum; (c) displays antibacterial activity; (d) binds to CD98, which mediates HBD3 internalization in eukaryotic cells; (e) exerts antiviral activity against human immunodeficiency virus and herpes simplex virus; and (f) is not toxic to human cells. These results demonstrate that the γ-core within HBD3 is the ancestral core of the full-length molecule and is a viable HDP per se, since it is endowed with the most important biological features of HBD3. Notably, the small, stable scaffold of the HBD3 γ-core can be exploited to design disease-specific antimicrobial agents.

PDZ Domain in the Engineering and Production of a Saporin Chimeric Toxin as a Tool for targeting Cancer Cells.

In this paper we have studied a PDZ protein domain as a possible tool for cellular targeting of the ribosome inactivating protein Saporin, exploiting the ability of PDZ domains to recognize and bind short peptide sequences located at the C-terminus of a cognate protein. We have focused our attention on the PDZ domain from hCASK (Human calcium/calmodulin-dependent serine protein kinase) that binds extracellular CD98 in epithelial cells, being this antigen recognized as a marker for several human tumors and particularly considered a negative prognostic marker for human glioblastoma. We produced recombinant fusions of one or two hCASK-PDZ domains with the ribosome inactivating protein Saporin and assayed them on two human glioblastoma cell lines (GL15 and U87). These constructs proved to be toxic, with increasing activity as a function of the number of PDZ domains, and induce cell death by apoptotic mechanisms in a dose-dependent and/or time dependent manner.

Targeting intestinal inflammation with CD98 siRNA/PEI-loaded nanoparticles.

Intestinal CD98 expression plays a crucial role in controlling homeostatic and innate immune responses in the gut. Modulation of CD98 expression in intestinal cells therefore represents a promising therapeutic strategy for the treatment and prevention of inflammatory intestinal diseases, such as inflammatory bowel disease. Here, the advantages of nanoparticles (NPs) are used, including their ability to easily pass through physiological barriers and evade phagocytosis, high loading concentration, rapid kinetics of mixing and resistance to degradation. Using physical chemistry characterizations techniques, CD98 siRNA/polyethyleneimine (PEI)-loaded NPs was characterized (diameter of ~480 nm and a zeta potential of -5.26 mV). Interestingly, CD98 siRNA can be electrostatically complexed by PEI and thus protected from RNase. In addition, CD98 siRNA/PEI-loaded NPs are nontoxic and biocompatible with intestinal cells. Oral administration of CD98/PEI-loaded NPs encapsulated in a hydrogel reduced CD98 expression in mouse colonic tissues and decreased dextran sodium sulfate-induced colitis in a mouse model. Finally, flow cytometry showed that CD98 was effectively downregulated in the intestinal epithelial cells and intestinal macrophages of treated mice. Finally, the results collectively demonstrated the therapeutic effect of "hierarchical nano-micro particles" with colon-homing capabilities and the ability to directly release "molecularly specific" CD98 siRNA in colonic cells, thereby decreasing colitis.

Ecto-phosphorylation of CD98 regulates cell-cell interactions.

Ecto-phosphorylation plays an important role in many cellular functions. The transmembrane glycoprotein CD98 contains potential phosphorylation sites in its extracellular C-terminal tail. We hypothesized that extracellular signaling through ecto-protein kinases (ePKs) might lead to ecto-phosphorylation of CD98 and influence its multiple functions, including its role in cell-cell interactions. Our results show that recombinant CD98 was phosphorylated in vitro by ePKs from Jurkat cells and by the commercial casein kinase 2 (CK2). Alanine substitutions at serines-305/307/309 or serines-426/430 attenuated CK2-mediated CD98 phosphorylation, suggesting that these residues are the dominant phosphorylation sites for CK2. Furthermore, CD98 expressed in the basolateral membranes of intestinal epithelial Caco2-BBE cells was ecto-phosphorylated by Jurkat cell-derived ePKs and ecto-CK2 was involved in this process. Importantly, cell attachment studies showed that the ecto-phosphorylation of CD98 enhanced heterotypic cell-cell interactions and that the extracellular domain of CD98, which possesses the serine phosphorylation sites, was crucial for this effect. In addition, phosphorylation of recombinant CD98 increased its interactions with Jurkat and Caco2-BBE cells, and promoted cell attachment and spreading. In conclusion, here we demonstrated the ecto-phosphorylation of CD98 by ePKs and its functional importance in cell-cell interactions. Our findings reveal a novel mechanism involved in regulating the multiple functions of CD98 and raise CD98 as a promising target for therapeutic modulations of cell-cell interactions.

Intestinal epithelial CD98: an oligomeric and multifunctional protein.

The intestinal epithelial cell-surface molecule, CD98 is a type II membrane glycoprotein. Molecular orientation studies have demonstrated that the C-terminal tail of human CD98 (hCD98), which contains a PDZ-binding domain, is extracellular. In intestinal epithelial cells, CD98 is covalently linked to an amino-acid transporter with which it forms a heterodimer. This heterodimer associates with beta(1)-integrin and intercellular adhesion molecular 1 (ICAM-1) to form a macromolecular complex in the basolateral membranes of polarized intestinal epithelial cells. This review focuses on the multifunctional roles of CD98, including involvement in extracellular signaling, adhesion/polarity, and amino-acid transporter expression in intestinal epithelia. A role for CD98 in intestinal inflammation, such as Intestinal Bowel Disease (IBD), is also proposed.

Identification of cell proliferation-associated epitope on CD98 oncoprotein using phage display random peptide library.

CD98 is known as a cell surface antigen expressed in proliferating normal tissues and in almost all tumor cells. Although the function of CD98 is not yet fully elucidated, it is suggested that CD98 is concerned functionally in lymphocyte activation, cell proliferation, and malignant transformation. Monoclonal antibody against human CD98 heavy chain (h.c.), termed HBJ127, shows inhibition of lymphocyte activation and tumor cell growth in vitro. These observations suggest that the epitope recognized by HBJ127 may be crucial for CD98 function. In the present study, the authors investigated the epitope recognized by HBJ127 using a phage display random heptapeptide library. Approximately 2.4 x 10(4)-fold amplification of eluted phage titer was obtained after three rounds of panning of the phage library against HBJ127. Seven different heptapeptide sequences were isolated from 30 randomly selected clones of the post-panning phage population. A homology search using ClustalW identified the peptide sequence corresponding to (442)AFS(444) of human CD98 h.c. It was also found that (443)F is a human-specific amino acid by comparing sequences of human, rat, and mouse origin. Reduced reactivity of HBJ127 was detected against the phenylalanine-substituted peptide but not detected against the alanine or serine-substituted one. It has been identified that HBJ127 reacts only with human species and the HBJ127 epitope position is predicted in 418-529 of human CD98 h.c. From these results and observations, it was estimated that (442)AFS(444) of human CD98 h.c. may be the HBJ127 epitope. Moreover, (443)F may be critical for the binding of HBJ127 against human CD98 h.c.

Bridge linkage role played by CD98hc of anti-tumor drug resistance and cancer metastasis on cisplatin-resistant ovarian cancer cells.

Anti-tumor drug resistance and cancer metastasis are always clinically coincidental, which are conducted by different molecules such as P-glycoprotein (P-gp) and CD147, respectively. P-gp and CD147/CD98hc complex are both found highly expressed on cisplatin resistant ovarian cancer cell line SKOV3/DDP but only slightly expressed on its parent cell SKOV3. RNAi targeting CD98hc or CD147 both reduce their own and P-gp expression as well as cisplatin IC50 of drug-resistant tumor cells. CD147 interference only reduced membrane CD98hc rather than its intracellular forms. Stop of CD98hc also diminished CD147 translation. Cloned potential CD98hc promoter region showed promoter activity in luciferase assay under cisplatin pressure. Intracellular cisplatin accumulation was found increased in RNAi groups and the efflux ability of cisplatin resistant SKOV3 cells was disrupted as well. CD147 has been reported to play an important role in tumor metastasis. Taken together, CD98hc was for the first time revealed to be a bridge between MDR phenotype and tumor metastasis.

CD98, a novel marker of transient amplifying human keratinocytes.

Identification of plasma membrane markers of basal keratinocytes is essential for sorting basal cells and, subsequently, adult epidermal stem cells. In this study, we isolated caveolin-1-enriched microdomains from human HaCaT keratinocytes and identified proteins representing potential cell surface markers of the epidermis by a proteomic approach. The purification of this caveolae domain allowed us to characterize 53 proteins of which 26% were transmembrane and 32% associated-membrane proteins. One of them, CD98, was found to be co-localized with beta1 integrin at the plasma membrane of the basal keratinocytes of healthy human epidermis. We then isolated CD98-positive keratinocytes from fresh skin biopsies. Using clonogenic assays, we demonstrate that CD98 may be considered as a marker of transient amplifying human keratinocytes.

Structure-function relationships of heterodimeric amino acid transporters.

Heterodimeric amino acid transporters mediate the transfer of amino acids between organs and between different cell types. Members of this particular family of amino acid transporters are constituted by a heavy chain and an associated light chain. The heavy chain is a type II membrane protein with an intracellular amino terminus, a single transmembrane helix, and a large extracellular domain. The light chain, in contrast, is a typical helix-bundle protein with 12 putative transmembrane helices. Two different heavy chains, designated 4F2hc and rbAT, and seven different light chains have been identified to date. Deletion studies indicate that the extracellular domain of the heavy chain has two subdomains. The carboxy-terminal tip of 4F2hc is critical for recognition of certain light chains, whereas the carboxy-terminal tip of rbAT is involved in substrate transport. Sequence alignments suggest that the major part of the extracellular domain forms an alpha/beta domain similar to bacterial alpha-amylases. A structural model of the rbAT extracellular domain is presented that is in agreement with experimental observations from several mutations and that aligns well with the alpha-amylase domain.

CD98-mediated links between amino acid transport and beta 1 integrin distribution in polarized columnar epithelia.

In non-polarized cells, CD98 has been shown to both influence beta(1) integrins and heterodimerize with LAT-2, which confers amino acid transport capability on the LAT-2/CD98 heterodimer. Since LAT-2 is most heavily expressed in intestine and CD98 associates with the beta(1) integrin splice form selectively found in such epithelia, we investigated the relationship and polarity of these proteins using the intestinal epithelial model Caco2-BBE. CD98 was found to selectively coimmunoprecipitate with both LAT-2 and beta(1) integrin, and, logically, all three proteins were polarized to the same (basolateral) domain. Furthermore, expression of CD98 in polarized epithelia lacking human CD98 (MDCK cells) disrupted beta(1) integrin surface distribution and cytoskeletal architecture, suggesting that CD98 can influence integrin function. Expression of a CD98 mutant lacking the specific residues conferring LAT-2 binding similarly affected cells, confirming that the latter effect was not due to LAT-2 sequestration. Use of CD98 truncation mutants suggest that a 10-amino acid domain located at the putative cytoplasmic tail/transmembrane domain interface was necessary and sufficient to induce the phenotype change. We conclude that the CD98/LAT-2 amino acid transporter is polarized to the same domain on which beta(1) integrin resides. CD98 appears to associate with beta(1) integrin and, in doing so, may influence its function as revealed by disruption of the outside-in signaling that confers cytoskeletal organization. Furthermore, such findings suggest a link between classic transport events and a critical element of barrier function: integrin-mediated influences on cytoskeletal organization.