RHAMM, a receptor for hyaluronan-mediated motility, compensates for CD44 in inflamed CD44-knockout mice: a different interpretation of redundancy

We report here that joint inflammation in collagen-induced arthritis is more aggravated in CD44-knockout mice than in WT mice, and we provide evidence for molecular redundancy as a causal factor. Furthermore, we show that under the inflammatory cascade, RHAMM (receptor for hyaluronan-mediated motility), a hyaluronan receptor distinct from CD44, compensates for the loss of CD44 in binding hyaluronic acid, supporting cell migration, up-regulating genes involved with inflammation (as assessed by microarrays containing 13,000 cDNA clones), and exacerbating collagen-induced arthritis. Interestingly, we further found that the compensation for loss of the CD44 gene does not occur because of enhanced expression of the redundant gene (RHAMM), but rather because the loss of CD44 allows increased accumulation of the hyaluronic acid substrate, with which both CD44 and RHAMM engage, thus enabling augmented signaling through RHAMM. This model enlightens several aspects of molecular redundancy, which is widely discussed in many scientific circles, but the processes are still ill defined.     

Expression of CD44 variant isoforms CD44v3 and CD44v6 is increased on T cells from patients with systemic lupus erythematosus and is correlated with disease activity

Objective

To quantify the expression of CD44 and variant isoforms CD44v3 and CD44v6 on T cells from patients with systemic lupus erythematosus (SLE), and to assess correlations of the level of expression of these molecules with disease manifestations.

Methods

Information on clinical and demographic characteristics was collected, and blood samples were obtained from 72 patients with SLE and 32 healthy control subjects matched to the patients by sex, race, and age. Expression of CD44 and variants CD44v3 and v6 on T cell subsets was determined by flow cytometry, and Pearson's correlations of their expression levels with clinical variables, SLE Disease Activity Index (SLEDAI) scores, and presence of lupus nephritis were determined. Wilcoxon's rank sum tests and conditional multivariable regression analyses were applied to identify differences in the expression of CD44 between patients with SLE and healthy controls.

Results

Expression of CD44 was higher on CD4+ and CD8+ T cells from SLE patients compared with controls (P ≤ 0.03). Expression of CD44v3 and CD44v6 was also higher on total T cells and CD4+ and CD8+ T cells from SLE patients compared with controls (P ≤ 0.03). Cell surface levels of CD44v3 on total T cells, CD4+ T cells, and CD8+ T cells as well as cell surface expression of CD44v6 on total T cells and CD4+ T cells were correlated with the SLEDAI score (P < 0.05). The presence of lupus nephritis was associated with the expression of CD44v6 on total T cells, CD4+ T cells, and CD4−CD8− T cells (P < 0.05). Positivity for anti–double‐stranded DNA antibodies was associated with the expression levels of CD44v6 on T cells (P < 0.05).

Conclusion

These results indicate that expression levels of CD44v3 and CD44v6 on T cells may represent useful biomarkers of SLE activity.

     

CD44 in hematological neoplasias

The CD44 protein family spans a large group of transmembrane glycoproteins acquired by alternative splicing and post-translational modifications. The great heterogeneity in molecular structure is reflected in its various important functions: CD44 mediates (1) interaction between cell and extracellular matrix, (2) signal submission, e.g., by acting as co-receptor for membrane-spanning receptor tyrosine kinases or by association with intracellular molecules initiating several signaling pathways, and (3) anchor function connecting to the cytoskeleton via the ezrin-radixin-moesin protein family. The expression pattern of the different CD44 isoforms display strong variations dependent on cell type, state of activation, and differentiation stage. In hematopoietic cells, CD44 mediates interaction of progenitor cells and bone marrow stroma during hematopoiesis, regulates maturation, and activation-induced cell death in T cells, influences neutrophil and macrophage migration as well as cytokine production, and participates in lymphocyte extravasation and migration. CD44 is involved in development and progress of hematological neoplasias by enhancement of apoptotic resistance, invasiveness, as well as regulation of bone marrow homing, and mobilization of leukemia-initiating cells into the peripheral blood. Thereby altered CD44 expression functions as marker for worse prognosis in most hematological malignancies. Additionally, CD44 expression levels can be used to distinguish between different hematological neoplasias and subtypes. Concerning new treatment strategies, CD44 displays promising potential either by direct targeting of CD44 expressed on the malignant cells or reversing an acquired resistance to primary treatment mediated through altered CD44 expression. The former can be achieved by antibody or hyaluronan-based immunotherapy.     

CD44与大肠癌

CD44与大肠癌@田慧军$武汉大学人民医院消化内科!武汉430060~~     

CD134 is a cellular receptor specific for human herpesvirus-6B entry

Human herpesvirus-6B (HHV-6B) is a T lymphotropic β-herpesvirus that is clearly distinct from human herpesvirus-6A (HHV-6A) according to molecular biological features. The International Committee on Taxonomy of Viruses recently classified HHV-6B as a separate species. The primary HHV-6B infection causes exanthem subitum and is sometimes associated with severe encephalopathy. More than 90% of the general population is infected with HHV-6B during childhood, and the virus remains throughout life as a latent infection. HHV-6B reactivation causes encephalitis in immunosuppressed patients. The cellular receptor for HHV-6A entry was identified as human CD46, but the receptor for HHV-6B has not been clear. Here we found that CD134, a member of the TNF receptor superfamily, functions as a specific entry receptor for HHV-6B. A T-cell line that is normally nonpermissive for HHV-6B infection became highly susceptible to infection when CD134 was overexpressed. CD134 was down-regulated in HHV-6B–infected T cells. Soluble CD134 interacted with the HHV-6B glycoprotein complex that serves as a viral ligand for cellular receptor, which inhibited HHV-6B but not HHV-6A infection in target cells. The identification of CD134 as an HHV-6B specific entry receptor provides important insight into understanding HHV-6B entry and its pathogenesis.     

An aggressive subtype of B-CLL is characterized by strong CD44 expression and lack of CD11c

In a retrospective study based on 107 B-CLL patients, the expression of the adhesion molecules CD44, CD11a, CD11b, CD11c, CD18, CD25 and CD54 was analysed in bone marrow cryostat sections by immunohistochemistry. CD44 expression clearly identified two subgroups of B-CLL patients with different clinical course. In particular, CD44-positive patients presented with advanced disease, more often displayed a diffuse pattern of bone marrow infiltration, and had a worse prognosis. 33/61 patients positive for CD44 died within the observation period compared to 7/46 patients negative for CD44 ( P  = 0.0012). Multivariate analysis emphasized the independent prognostic value of CD44 expression for overall survival ( P  = 0.022). In contrast, patients positive for CD11c showed a longer survival, with 9/40 patients dying within the observation period compared to 31/67 negative for CD11c ( P  = 0.0013). Patients lacking CD11c were in advanced Rai and Binet stage. Multivariate analysis confirmed CD11c as a relevant independent prognostic marker ( P  = 0.033). Moreover, CD11c was able to separate patients with significantly different prognosis in the subgroup of CD44-positive cases. 4/18 patients positive for CD44 and CD11c died before median survival time was reached. Patients positive for CD44 but negative for CD11c had an adverse prognosis: 29/43 patients died, median survival time was 33.4 months.   Our results indicate that CD44 positivity and CD11c negativity are associated with more advanced disease and worse prognosis in B-CLL and suggest CD44-positive/CD11c-negative cases represent a more aggressive form of the disease.     

A distinct glycoform of CD44 is an L-selectin ligand on human hematopoietic cells

We previously have obtained operational evidence of a hematopoietic cell L-selectin ligand expressed on normal human hematopoietic cells and on leukemic blasts. Using a technique developed in our laboratory for analyzing and identifying adhesion molecules, we show here that hematopoietic cell L-selectin ligand is a specialized glycoform of CD44. This L-selectin ligand activity of CD44 requires sialofucosylated N-linked glycans and is sulfation-independent. These data provide important insights on the structural biology of CD44 and reveal a role for this protein as an L-selectin ligand on human hematopoietic cells.     

CD31 is a key coinhibitory receptor in the development of immunogenic dendritic cells

CD31 is a transhomophilic tyrosine-based inhibitory motif receptor and is expressed by both dendritic cells (DCs) and T lymphocytes. Previous studies have established that the engagement of CD31 drives immune-inhibitory signaling in T lymphocytes, but the effect exerted by CD31 signaling in DCs remains elusive. Here, we show that CD31 is a key coinhibitory receptor on stimulated DCs, favoring the development of tolerogenic functions and finally resulting in T-cell tolerance. The disruption of CD31 signaling favored the immunogenic maturation and migration of resident DCs to the draining lymph nodes. In contrast, sustaining the CD31/SHP-1 signaling during DC maturation resulted in reduced NF-κB nuclear translocation, expression of costimulatory molecules, and production of immunogenic cytokines (e.g., IL-12, IL-6), whereas the expression of TGF-β and IL-10 were increased. More importantly, CD31-conditioned DCs purified from the draining lymph nodes of ovalbumin-immunized mice favored the generation of antigen-specific regulatory T cells (CD25⁺ forkhead box P3⁺) at the expense of effector (IFN-γ⁺) cells upon coculture with naive ovalbumin-specific CD4⁺ T lymphocytes ex vivo. Finally, the adoptive transfer of CD31-conditioned myelin oligodendrocyte glycoprotein-loaded DCs carried immune tolerance against the subsequent development of MOG-induced experimental autoimmune encephalomyelitis in vivo. The key coinhibitory role exerted by CD31 on DCs highlighted by the present study may have important implications both in settings where the immunogenic function of DCs is desirable, such as infection and cancer, and in settings where tolerance-driving DCs are preferred, such as autoimmune diseases and transplantation.Dendritic cells (DCs) have an essential function in initiating CD4⁺ T-cell responses by recognizing and presenting specific antigens associated with danger signals (1, 2). These signals contribute to conferring a fully mature, immunogenic phenotype to DCs, which is characterized by the up-regulation of MHC costimulatory molecules (e.g., CD40, CD86, CD80). The ensuing up-regulation of the chemokine (C-C motif) receptor type 7 (CCR7) receptor enables the migration of DCs to draining lymph nodes following the chemokine (C-C) motif ligand 21 (CCL21) gradient (3, 4). Finally, the fully matured DCs produce the proinflammatory cytokines IL-1β, TNF, IL-12, and IL-6 (5). Importantly, DCs can also exert the opposite function by tolerizing T cells against self-antigen–directed immune responses, which is necessary to minimize autoimmune reactions. However, insufficient DC immunogenicity and excessive tolerance would favor the development of chronic infections and tumors. The immunogenic function of DCs depends on the balance between activating and inhibitory signals that occur at the time of DC maturation (2).Elucidating the inhibitory receptors that are involved in the control of DC maturation would facilitate new interventional strategies to control autoimmune diseases. Despite intensive work in this area (6), the coinhibitory receptors involved in the control of DC immunogenic functions remain poorly understood. Ig-like immunoreceptor tyrosine-based inhibitory motif (ITIM) receptors are thought to play an essential role in inhibiting the maturation of DCs (7).Among the Ig-like ITIM receptors, we propose that CD31 (8, 9) (also known as PECAM-1) may play an important role in DC function because CD31 is constitutively expressed on these cells (10). Moreover, CD31 is essentially engaged by homophilic binding (11), which remarkably occurs between interacting cells of the innate and adaptive immune system.The low-affinity, transhomophilic engagement of CD31 (11) triggers downstream inhibitory signaling (9), leads to the detachment of CD31⁺ lymphocytes from the cells of the innate immune system (12), and raises the activation threshold of lymphocytes via the phosphorylation of CD31 ITIMs and the recruitment of SH2 domain-containing tyrosine phosphatase (e.g., SHP-1, SHP-2) upon the engagement of the antigen receptor (13–16). Nevertheless, the role played by CD31 in maturing DCs remains to be elucidated.Interestingly, it has been shown that during LPS-driven maturation, CD31 expression is consistently reduced on human monocyte-derived DCs (17–19) and endotoxin-induced septic shock is exaggerated in CD31^−/− mice (20, 21). In addition, autoimmune disease models dependent on antigen presentation are accelerated in the absence of CD31 (22, 23), suggesting that the effective presentation of the immunizing antigens involved in specific adaptive immune responses is favored by the absence of CD31.Here, we demonstrate that the disruption of CD31 signaling favors the maturation and subsequent migration of antigen-loaded DCs to the draining lymphoid organs, driving more rapid and effective antigen-specific T-cell responses. In contrast, upholding the CD31/SH2 domain-containing tyrosine phosphatase-signaling pathway with an agonist peptide reduces the extent of maturation of the DCs, which become tolerogenic toward recall antigens both in vitro and in vivo.     

CD44v17在胃癌组织中的表达及其与临床生物学特性之间的关系

目的 探讨一种新的CD44变异体（CD44v17）在胃癌组织中的表达及其与临床生物学特性之间的关系.方法根据本实验室在MCF-7／Adr中新发现的1种CD44剪切拼接变异体CD44v17设计特异性引物,应用SYBR Green I荧光染料,采用实时PCR法检测87例胃癌组织及相应癌旁组织CD44v17 Mrna的表达,根据标准曲线计算CD44v17mRNA的表达量,分析CD44v17mRNA表达与胃癌临床生物学特性之间的关系.结果胃癌组织CD44v17 Mrna表达明显高于相应癌旁正常组织（P〈0.05）;肿瘤〉5 cm组CD44v17 Mrna表达与肿瘤≤5 cm组表达比较差异无显著性（P〉0.05）;未分化腺癌组表达明显高于乳头状腺癌及管状腺癌组（P〈0.05）,乳头状腺癌组CD44v17 Mrna表达与管状腺癌组比较差异无显著性（P〉0.05）;肿瘤累及浆膜及浆膜外组CD44v17 Mrna表达显著高于侵及黏膜、黏膜下层及肌层组（P〈0.05）,而肿瘤侵及黏膜及黏膜下层组的CD44v17 Mrna表达与侵犯肌层组表达比较差异无显著性（P〉0.05）.淋巴结转移组CD44v17 Mrna表达明显高于淋巴结无转移组（P〈0.05）;有肝脏转移组CD44v17 Mrna表达显著高于无肝脏转移组（P〈0.05）.结论CD44v17 Mrna在胃癌组织中高表达,可能与胃癌的侵袭、转移及预后有关.