Biomedical subjects

Hsiu-Ching Chang

Publications and source records attributed to Hsiu-Ching Chang.

8 recordsLinked to original sources

PubMed2006

CD8alphabeta has two distinct binding modes of interaction with peptide-major histocompatibility complex class I.

Interaction of CD8 (CD8alphaalpha or CD8alphabeta) with the peptide-major histocompatibility complex (MHC) class I (pMHCI) is critical for the development and function of cytolytic T cells. Although the crystal structure of CD8alphaalpha.pMHCI complex revealed that two symmetric CD8alpha subunits interact with pMHCI asymmetrically, with one subunit engaged in more extensive interaction than the other, the details of the interaction between the CD8alphabeta heterodimer and pMHCI remained unknown. The Ig-like domains of mouse CD8alphabeta and CD8alphaalpha are similar in the size, shape, and surface electrostatic potential of their pMHCI-binding regions, suggesting that their interactions with pMHCI could be very similar. Indeed, we found that the CD8alpha variants CD8alpha(R8A) and CD8alpha(E27A), which were functionally inactive as homodimers, could form an active co-receptor with wild-type (WT) CD8beta as a CD8alpha(R8A)beta or CD8alpha(E27A)beta heterodimer. We also identified CD8beta variants that could form active receptors with WT CD8alpha but not with CD8alpha(R8A). This observation is consistent with the notion that the CD8beta subunit may replace either CD8alpha subunit in CD8alphaalpha.pMHCI complex. In addition, we showed that both anti-CD8alpha and anti-CD8beta antibodies were unable to completely block the co-receptor activity of WT CD8alphabeta. We propose that CD8alphabeta binds to pMHCI in at least two distinguishable orientations.

Amino Acid Sequence↗

PubMed2006

The TCR C beta FG loop regulates alpha beta T cell development.

The TCRbeta chain constant domain contains an unusually elongated, solvent-exposed FG loop. This structural element forms one component of an alphabeta TCR cavity against which CD3epsilongamma may abut to facilitate Ag-specific signaling. Consistent with this notion, in the present study we show that N15alphabeta TCR transfectants expressing a FG loop-deleted chain (betaDeltaFG) stimulate less tyrosine protein phosphorylation than those bearing a wild-type beta-chain (betawt) upon TCR cross-linking. Furthermore, coimmunoprecipitation studies suggest a weakened association between the CD3epsilongamma heterodimer and the beta-chain in TCR complexes containing the betaDeltaFG variant. To further investigate the biologic role of the Cbeta FG loop in development, we competitively reconstituted the thymus of Ly5 congenic or RAG-2-/- mice using bone marrow cells from betawt or betaDeltaFG transgenic C57BL/6 (B6) mice. Both betawt and betaDeltaFG precursor cells generate thymocytes representative of all maturational stages. However, betaDeltaFG-expressing thymocytes dominate during subsequent development, resulting in an excess of betaDeltaFG-expressing peripheral T cells with reduced proliferative and cytokine production abilities upon TCR stimulation. Collectively, our results show that the unique Cbeta FG loop appendage primarily controls alphabeta T cell development through selection processes.

Animals↗

PubMed2005

Structural and mutational analyses of a CD8alphabeta heterodimer and comparison with the CD8alphaalpha homodimer.

The crystal structure of a recombinant mouse single chain CD8alphabeta ectodomains at 2.4 A resolution reveals paired immunoglobulin variable region-like domains with a striking resemblance to CD8alphaalpha in size, shape, and surface electrostatic potential of complementarity-determining regions (CDR), despite <20% sequence identity between the CD8alpha and CD8beta subunits. Unlike the CD8alpha subunit(s) in the heterodimer or homodimer, the CDR1 loop of CD8beta tilts away from its corresponding CDR2 and CDR3 loops. Consistent with this observation, independent mutational studies reveal that alanine substitutions of residues in the CDR1 loop of CD8beta have no effect on CD8alphabeta coreceptor function, whereas mutations in CD8beta CDR2 and CDR3 loops abolish CD8alphabeta coreceptor activity. The implications of these findings and additional CD8alpha mutational studies for CD8alphabeta- versus CD8alphaalpha-MHCI binding are discussed.

Amino Acid Sequence↗

PubMed2005

CD44 splicing pattern is associated with disease progression in pulmonary adenocarcinoma.

BACKGROUND AND PURPOSE: Certain alternatively spliced exons of CD44 gene have been associated with specific functions. However, these functions may have come from inclusion of a central array of alternatively spliced exons, rather than a single one. The goals of this study were to analyze all of the variant exons included by alternative splicing, the entire population of CD44 mRNA transcripts, and the prognostic implications of CD44 mRNA and protein isoforms expressed by non-small cell lung cancer (NSCLC). METHODS: Using a polymerase chain reaction protocol with short reaction times, we amplified, sequenced and quantified CD44 mRNA transcripts from 52 samples of NSCLC to determine the splicing patterns of alternatively included exons and the proportion of each CD44 mRNA transcript. The expression of CD44 standard form and variant isoforms CD44v3 and CD44v6 were also analyzed by immunohistochemistry (IHC). RESULTS: Normal lung and NSCLC expressed CD44 mRNA transcripts containing variant exons v10, v8-10, v6-10, v3-10 and v2-10. In squamous cell carcinoma, the expression rates of these mRNA transcripts were equal to or higher than those of the normal lung, and the splicing pattern was not associated with disease progression. In adenocarcinoma, the expression rates of CD44v6-10, v3-10 and v2-10 mRNA were lower than in normal lung. The down-regulation of CD44v6-10, CD44v3-10 mRNA and CD44v6 protein paralleled the progression of adenocarcinoma. Recurrence of adenocarcinoma was associated with negative expression of CD44v6-10 or CD44v3-10 mRNA, and with low-level expression of CD44v6 or CD44v3 by IHC. Negative expression of CD44v6-10 mRNA and reduced expression of CD44 v6 protein were associated with a shorter disease-free and overall survival in the univariate but not the multivariate analysis. CONCLUSION: Our data suggest that CD44 splicing pattern is associated with disease progression in adenocarcinoma.

Adenocarcinoma↗

PubMed2004

Phage-displayed libraries of peptide/major histocompatibility complexes.

Characterizing peptide epitopes targeted by major histocompatibility complex (MHC)-restricted T cells of unknown specificity would have broad implications. In this article we introduce and validate an original phage-displayed library of noncovalent complexes of peptide and MHC (P/MHC). We show that soluble MHC molecules associate with peptides presented by a phage, thereby resulting in the formation of multivalent P/MHC phages. Complex formation is stabilized by the interaction of the soluble partner (MHC) with two components, peptide and beta2-microglobulin, both of which are covalently linked to the phage. As proof of concept, we have used this strategy to express peptide libraries in the context of H-2K(b). Using monoclonal antibody 25D (specific for ovalbumin/H-2K(b)) as a template to screen the library, we were able to select a variant epitope functionally and structurally related to the wild-type peptide. Interaction studies between monoclonal antibody 25D and cells suggest that the variant peptide has been selected on the basis of a decreased dissociation rate between the peptide/H-2K(b) complex and its ligand. A weak agonist of the N15 TCR (vesicular stomatitis virus/H-2K(b)-specific) was also isolated from another P/MHC library. This strategy opens up new perspectives for antigen discovery and the manipulation of T cell responses.

Amino Acid Sequence↗

PubMed2003

Stalk region of beta-chain enhances the coreceptor function of CD8.

CD8 glycoproteins are expressed as either alphaalpha homodimers or alphabeta heterodimers on the surface of T cells. CD8alphabeta is a more efficient coreceptor than the CD8alphaalpha for peptide Ag recognition by TCR. Each CD8 subunit is composed of four structural domains, namely, Ig-like domain, stalk region, transmembrane region, and cytoplasmic domain. In an attempt to understand why CD8alphabeta is a better coreceptor than CD8alphaalpha, we engineered, expressed, and functionally tested a chimeric CD8alpha protein whose stalk region is replaced with that of CD8beta. We found that the beta stalk region enhances the coreceptor function of chimeric CD8alphaalpha to a level similar to that of CD8alphabeta. Surprisingly, the beta stalk region also restored functional activity to an inactive CD8alpha variant, carrying an Ala mutation at Arg(8) (R8A), to a level similar to that of wild-type CD8alphabeta. Using the R8A variant of CD8alpha, a panel of anti-CD8alpha Abs, and three MHC class I (MHCI) variants differing in key residues known to be involved in CD8alpha interaction, we show that the introduction of the CD8beta stalk leads to a different topology of the CD8alpha-MHCI complex without altering the overall structure of the Ig-like domain of CD8alpha or causing the MHCI to employ different residues to interact with the CD8alpha Ig domain. Our results show that the stalk region of CD8beta is capable of fine-tuning the coreceptor function of CD8 proteins as a coreceptor, possibly due to its distinct protein structure, smaller physical size and the unique glycan adducts associated with this region.

Adjuvants, Immunologic↗

PubMed2003

Polygonum multiflorum extracts improve cognitive performance in senescence accelerated mice.

The objective of this study was to investigate the effects of Polygonum multflorum (PM) Thunb. on the learning and memory ability in one and seven-month-old male senescence accelerated mice (SAMP8). The mice were fed with two different diets for 18 weeks; they were casein dietary group (control group) and casein diet supplemented with PM extracts. Active shuttle avoidance test was performed to determine the learning and memory ability of the mice while the spongy degeneration and the lipofuscin, malondialdehyde, and total thiol levels of the brain were measured to evaluate the extent of the brain degeneration and oxidative status. Results of active shuttle avoidance test showed the mice fed with the PM extracts had significantly better learning and memory ability than the control group. The spongy degeneration and the lipofuscin and malondialdehyde concentrations of the mice in the PM groups were significantly lower than the control in both age groups, whereas the total thiol levels were higher but not significantly different. It was concluded that the supplement of the PM extracts could improve the learning and memory ability and reduce the brain pathological changes in mice. This might be due to the antioxidant phytochemicals of the PM extracts.

Aging↗

PubMed2002

Involvement of the TCR Cbeta FG loop in thymic selection and T cell function.

The asymmetric disposition of T cell receptor (TCR) Cbeta and Calpha ectodomains creates a cavity with a side-wall formed by the rigid Cbeta FG loop. To investigate the significance of this conserved structure, we generated loop deletion (betaDeltaFG) and betawt transgenic (tg) mice using the TCR beta subunit of the N15 CTL. N15betawt and N15betaDeltaFG H-2(b) animals have comparable numbers of thymocytes in S phase and manifest developmental progression through the CD4(-)CD8(-) double-negative (DN) compartment. N15betaDeltaFG facilitates transition from DN to CD4(+)8(+) double-positive (DP) thymocytes in recombinase activating gene (RAG)-2(-/-) mice, showing that pre-TCR function remains. N15betaDeltaFG animals possess approximately twofold more CD8(+) single-positive (SP) thymocytes and lymph node T cells, consistent with enhanced positive selection. As an altered Valpha repertoire observed in N15betaDeltaFG mice may confound the deletion's effect, we crossed N15alphabeta TCR tg RAG-2(-/-) with N15betaDeltaFG tg RAG-2(-/-) H-2(b) mice to generate N15alphabeta RAG-2(-/-) and N15alphabeta.betaDeltaFG RAG-2(-/-) littermates. N15alphabeta.betaDeltaFG RAG-2(-/-) mice show an 8-10-fold increase in DP thymocytes due to reduced negative selection, as evidenced by diminished constitutive and cognate peptide-induced apoptosis. Compared with N15alphabeta, N15alphabeta.betaDeltaFG T cells respond poorly to cognate antigens and weak agonists. Thus, the Cbeta FG loop facilitates negative selection of thymocytes and activation of T cells.

Amino Acid Sequence↗