The tetraspanin CD151 functions as a negative regulator in the adhesion-dependent activation of Ras

CD151 enrichment in exosomes of luminal androgen receptor breast cancer cell line contributes to cell invasion

Breast cancer is the most common and highly heterogeneous disease in women worldwide. Given the challenges in the treatment of advanced metastatic breast cancer, it is necessary to understand the molecular mechanisms related to disease progression. Exosomes play various roles in the progression of tumors, including promoting the invasion and advancing the distant metastasis. To study the molecular mechanisms related to the progression of luminal androgen receptor (LAR) breast cancer, we first isolated exosomes of MDA-MB-453 cells, a representative cell line of LAR. Through quantitative proteomic analysis, we identified 180 proteins specifically enriched in exosomes after comparing with those in cells, microvesicles, and the 150K supernatant. Among these, CD151, a protein involved in the regulation of cell motility was the most enriched one. CD151-knockdown exosomes reduced the invasion ability of the recipient breast cancer cell and lowered the phosphorylation level of tyrosine-protein kinase Lck, indicating that the invasion of LAR breast cancer may be due to CD151-enriched exosomes. Our work reports for the first time that CD151 was highly abundant in the exosomes of MDA-MB-453 cells and expands the understanding of the development process of LAR subtype, suggesting CD151 may be a potential candidate for the treatment of LAR breast cancer.

The tetraspanin CD151 marks a unique population of activated human T cells

Tetraspanins are a family of proteins with an array of functions that are well studied in cancer biology, but their importance in immunology is underappreciated. Here we establish the tetraspanin CD151 as a unique marker of T-cell activation and, in extension, an indicator of elevated, systemic T-cell activity. Baseline CD151 expression found on a subset of T-cells was indicative of increased activation of the MAPK pathway. Following TCR/CD3 activation, CD151 expression was upregulated on the overall T-cell population, a quintessential feature of an activation marker. CD151+ T-cell frequencies in the spleen, an organ with increased immune activity, were twice as high as in paired peripheral blood samples. This CD151+ T-cell frequency increase was not paralleled by an increase of CD25 or CD38, demonstrating that CD151 expression is regulated independently of other T-cell activation markers. CD151+ T-cells were also more likely to express preformed granzyme B, suggesting that CD151+ T cells are pro-inflammatory. To this end, HIV-1 patients on antiretroviral therapy who are reported to exhibit chronically elevated levels of immune activity, had significantly higher CD4+CD151+ T-cell frequencies than healthy controls, raising the possibility that proinflammatory CD151+ T cells could contribute to the premature immunological aging phenotype observed in these patients.

Genome-wide promoter methylation of hairy cell leukemia

Classic hairy cell leukemia (HCL) is a tumor of mature clonal B cells with unique genetic, morphologic, and phenotypic features. DNA methylation profiling has provided a new tier of investigation to gain insight into the origin and behavior of B-cell malignancies; however, the methylation profile of HCL has not been specifically investigated. DNA methylation profiling was analyzed with the Infinium HumanMethylation27 array in 41 mature B-cell tumors, including 11 HCL, 7 splenic marginal zone lymphomas (SMZLs), and chronic lymphocytic leukemia with an unmutated (n = 7) or mutated (n = 6) immunoglobulin gene heavy chain variable (IGHV) region or using IGHV3-21 (n = 10). Methylation profiles of nontumor B-cell subsets and gene expression profiling data were obtained from public databases. HCL had a methylation signature distinct from each B-cell tumor entity, including the closest entity, SMZL. Comparison with normal B-cell subsets revealed the strongest similarity with postgerminal center (GC) B cells and a clear separation from pre-GC and GC cellular programs. Comparison of the integrated analysis with post-GC B cells revealed significant hypomethylation and overexpression of BCR-TLR-NF-κB and BRAF-MAPK signaling pathways and cell adhesion, as well as hypermethylation and underexpression of cell-differentiation markers and methylated genes in cancer, suggesting regulation of the transformed hairy cells through specific components of the B-cell receptor and the BRAF signaling pathways. Our data identify a specific methylation profile of HCL, which may help to distinguish it from other mature B-cell tumors.

CD151 Expression Is Associated with a Hyperproliferative T Cell Phenotype

The tetraspanin CD151 is a marker of aggressive cell proliferation and invasiveness for a variety of cancer types. Given reports of CD151 expression on T cells, we explored whether CD151 would mark T cells in a hyperactivated state. Consistent with the idea that CD151 could mark a phenotypically distinct T cell subset, it was not uniformly expressed on T cells. CD151 expression frequency was a function of the T cell lineage (CD8 > CD4) and a function of the memory differentiation state (naive T cells < central memory T cells < effector memory T cells < T effector memory RA⁺ cells). CD151 and CD57, a senescence marker, defined the same CD28^- T cell populations. However, CD151 also marked a substantial CD28⁺ T cell population that was not marked by CD57. Kinome array analysis demonstrated that CD28⁺CD151⁺ T cells form a subpopulation with a distinct molecular baseline and activation phenotype. Network analysis of these data revealed that cell cycle control and cell death were the most altered process motifs in CD28⁺CD151⁺ T cells. We demonstrate that CD151 in T cells is not a passive marker, but actively changed the cell cycle control and cell death process motifs of T cells. Consistent with these data, long-term T cell culture experiments in the presence of only IL-2 demonstrated that independent of their CD28 expression status, CD151⁺ T cells, but not CD151^- T cells, would exhibit an Ag-independent, hyperresponsive proliferation phenotype. Not unlike its reported function as a tumor aggressiveness marker, CD151 in humans thus marks and enables hyperproliferative T cells.

Tetraspanin CD151 Promotes Initial Events in Human Cytomegalovirus Infection

Human cytomegalovirus (HCMV), a betaherpesvirus, can cause life-threatening disease in immunocompromised individuals. Viral envelope glycoproteins that mediate binding to and penetration into target cells have been identified previously. In contrast, cellular proteins supporting HCMV during entry are largely unknown. In order to systematically identify host genes affecting initial steps of HCMV infection, a targeted RNA interference screen of 96 cellular genes was performed in endothelial cells by use of a virus strain expressing the full set of known glycoprotein H and L (gH/gL) complexes. The approach yielded five proviral host factors from different protein families and eight antiviral host factors, mostly growth factor receptors. The tetraspanin CD151 was uncovered as a novel proviral host factor and was analyzed further. Like endothelial cells, fibroblasts were also less susceptible to HCMV infection after CD151 depletion. Virus strains with different sets of gH/gL complexes conferring either broad or narrow cell tropism were equally impaired. Infection of CD151-depleted cells by a fluorescent virus with differentially labeled capsid and envelope proteins revealed a role of CD151 in viral penetration but not in adsorption to the cell. In conclusion, the tetraspanin CD151 has emerged as a novel host factor in HCMV entry and as a putative antiviral target.

IMPORTANCE

At present, the events at the virus-cell interface and the cellular proteins involved during the HCMV entry steps are scarcely understood. In this study, several host factors with putative roles in this process were identified. The tetraspanin CD151 was discovered as a previously unrecognized proviral host factor for HCMV and was found to support viral penetration into the target cells. The findings of this study shed light on the cellular contribution during the initial steps of HCMV infection and open a new direction in HCMV research.

Function and Dynamics of Tetraspanins during Antigen Recognition and Immunological Synapse Formation

Tetraspanin-enriched microdomains (TEMs) are specialized membrane platforms driven by protein–protein interactions that integrate membrane receptors and adhesion molecules. Tetraspanins participate in antigen recognition and presentation by antigen-­presenting cells (APCs) through the organization of pattern-recognition receptors (PRRs) and their downstream-induced signaling, as well as the regulation of MHC-II–peptide trafficking. T lymphocyte activation is triggered upon specific recognition of antigens present on the APC surface during immunological synapse (IS) formation. This dynamic process is characterized by a defined spatial organization involving the compartmentalization of receptors and adhesion molecules in specialized membrane domains that are connected to the underlying cytoskeleton and signaling molecules. Tetraspanins contribute to the spatial organization and maturation of the IS by controlling receptor clustering and local accumulation of adhesion receptors and integrins, their downstream signaling, and linkage to the actin cytoskeleton. This review offers a perspective on the important role of TEMs in the regulation of antigen recognition and presentation and in the dynamics of IS architectural organization.

The Expression of CD9 and PIK3CD is Associated with Prognosis of Follicular Lymphoma

BACKGROUND

Follicular lymphoma (FL) frequently develops drug-resistance and transforms into more aggressive subtypes over time. It is urgent to find prognostic biomarkers and disclose signaling pathways that have potential to be drug targets. In this study, we investigated the association of FL prognosis with the expression of 2 proteins: PIK3CD, a PI3K pathway component, and CD9, a tetraspanin family member.

METHOD

The expression of PIK3CD and CD9 were examined on 76 FL tumor tissues and 15 normal tissues with Immunohistochemistry. Chi-square test, Cox proportional hazards model, and Kaplan-Meier estimates were used to analyze the relationships of CD9 and PIK3CD expression and major clinicopathological features.

RESULT

PIK3CD expression was significantly higher, whereas CD9 expression was significantly lower in the 76 FL specimens than normal tissues. Concomitantly, low CD9 or high PIK3CD expression is associated with high degrees of Ann Arbor stages. In agreement with this, PIK3CD is an unfavorable and CD9 is a favorable factor for progression-free survival (PFS). Interestingly, PIK3CD expression is negatively correlated with CD9 expression, and the PIK3CD-high/CD9-low was significantly associated with short PFS when the 2 factors were combined together. Lastly, CD9 expression was significant higher in patients with bone marrow infiltration (BMI) than those without BMI.

CONCLUSION

Both CD9 and PIK3CD are prognostic markers of FL. The negative correlation between CD9 and PIK3CD expression suggests that there may be crosstalks of the 2 proteins in FL.

CD151 promotes α3β1 integrin-dependent organization of carcinoma cell junctions and restrains collective cell invasion

Integrins function in collective migration both as major receptors for extracellular matrix and by crosstalk to adherens junctions. Despite extensive research, important questions remain about how integrin signaling mechanisms are integrated into collective migration programs. Tetraspanins form cell surface complexes with a subset of integrins and thus are good candidates for regulating the balance of integrin functional inputs into cell-matrix and cell-cell interactions. For example, tetraspanin CD151 directly associates with α3β1 integrin in carcinoma cells and promotes rapid α3β1-dependent single cell motility, but CD151 also promotes organized adherens junctions and restrains collective carcinoma cell migration on 2D substrates. However, the individual roles of CD151s integrin partners in CD151s pro-junction activity in carcinoma cells were not well understood. Here we find that CD151 promotes organized carcinoma cell junctions via α3β1 integrin, by a mechanism that requires the a3b1 ligand, laminin-332. Loss of CD151 promotes collective 3D invasion and growth in vitro and in vivo, and the enhanced invasion of CD151-silenced cells is α3 integrin dependent, suggesting that CD151 can regulate the balance between α3β1s pro-junction and pro-migratory activities in collective invasion. An analysis of human cancer cases revealed that changes in CD151 expression can be linked to either better or worse clinical outcomes depending on context, including potentially divergent roles for CD151 in different subsets of breast cancer cases. Thus, the role of the CD151-α3β1 complex in carcinoma progression is context dependent, and may depend on the mode of tumor cell invasion.

Tetraspanin CD151 Is a Negative Regulator of FcεRI-Mediated Mast Cell Activation

Mast cells are critical in the pathogenesis of allergic disease due to the release of preformed and newly synthesized mediators, yet the mechanisms controlling mast cell activation are not well understood. Members of the tetraspanin family are recently emerging as modulators of FcεRI-mediated mast cell activation; however, mechanistic understanding of their function is currently lacking. The tetraspanin CD151 is a poorly understood member of this family and is specifically induced on mouse and human mast cells upon FcεRI aggregation but its functional effects are unknown. In this study, we show that CD151 deficiency significantly exacerbates the IgE-mediated late phase inflammation in a murine model of passive cutaneous anaphylaxis. Ex vivo, FcεRI stimulation of bone marrow-derived mast cells from CD151(-/-) mice resulted in significantly enhanced expression of proinflammatory cytokines IL-4, IL-13, and TNF-α compared with wild-type controls. However, FcεRI-induced mast cell degranulation was unaffected. At the molecular signaling level, CD151 selectively regulated IgE-induced activation of ERK1/2 and PI3K, associated with cytokine production, but had no effect on the phospholipase Cγ1 signaling, associated with degranulation. Collectively, our data indicate that CD151 exerts negative regulation over IgE-induced late phase responses and cytokine production in mast cells.

Tetraspanins CD9 and CD151 at the immune synapse support T-cell integrin signaling

Understanding how the immune response is activated and amplified requires detailed knowledge of the stages in the formation of the immunological synapse (IS) between T lymphocytes and antigen-presenting cells (APCs). We show that tetraspanins CD9 and CD151 congregate at the T-cell side of the IS. Silencing of CD9 or CD151 blunts the IL-2 secretion and expression of the activation marker CD69 by APC-conjugated T lymphocytes, but does not affect the accumulation of CD3 or actin to the IS, or the translocation of the microtubule-organizing center toward the T-B contact area. CD9 or CD151 silencing diminishes the relocalization of α4β1 integrin to the IS and reduces the accumulation of high-affinity β1 integrins at the cell-cell contact. These changes are accompanied by diminished phosphorylation of the integrin downstream targets FAK and ERK1/2. Our results suggest that CD9 and CD151 support integrin-mediated signaling at the IS.

The tetraspanin gene MaPls1 contributes to virulence by affecting germination, appressorial function and enzymes for cuticle degradation in the entomopathogenic fungus, Metarhizium acridum

In most eukaryotes, tetraspanins regulate cellular activities by associating with other membrane components. In phytopathogenic fungi, the tetraspanin Pls1 controls appressorium-mediated penetration. However, regulation of Pls1 and its associated signalling pathways are not clear. In this study, the MaPls1 gene from the entomopathogenic fungus Metarhizium acridum was functionally characterized. MaPls1 was highly expressed in mycelium and appressorium, and accumulated on the plasma membrane or in the cytoplasm. Compared with a wild-type strain, the deletion mutant ΔMaPls1 had delayed germination and appressorium formation and impaired turgor pressure on locust wings, but normal germination on medium and non-host insect matrices. Bioassays showed that ΔMaPls1 had decreased virulence and hyphal body formation in haemolymph when topically inoculated, but was not different from wild type when the insect cuticle was bypassed. Moreover, the ability to grow out of the cuticle was impaired in ΔMaPls1. Digital gene expression profiling revealed that genes involved in hydrolysing host cuticle and cell wall synthesis and remodelling were downregulated in ΔMaPls1. MaPls1 participated in crosstalk with signalling pathways such as the cyclic adenosine monophosphate-dependent protein kinase A and calmodulin-dependent pathways. Taken together, these results demonstrated the important roles of MaPls1 at the early stage of infection-associated development in M. acridum.

Tetraspanin CD151 stimulates adhesion-dependent activation of Ras, Rac, and Cdc42 by facilitating molecular association between β1 integrins and small GTPases

Tetraspanin CD151 associates with laminin-binding α(3)β(1)/α(6)β(1) integrins in epithelial cells and regulates adhesion-dependent signaling events. We found here that CD151 plays a role in recruiting Ras, Rac1, and Cdc42, but not Rho, to the cell membrane region, leading to the formation of α(3)β(1)/α(6)β(1) integrin-CD151-GTPases complexes. Furthermore, cell adhesion to laminin enhanced CD151 association with β(1) integrin and, thereby, increased complex formation between the β(1) family of integrins and small GTPases, Ras, Rac1, and Cdc42. Adhesion receptor complex-associated small GTPases were activated by CD151-β(1) integrin complex-stimulating adhesion events, such as α(3)β(1)/α(6)β(1) integrin-activating cell-to-laminin adhesion and homophilic CD151 interaction-generating cell-to-cell adhesion. Additionally, FAK and Src appeared to participate in this adhesion-dependent activation of small GTPases. However, engagement of laminin-binding integrins in CD151-deficient cells or CD151-specific siRNA-transfected cells did not activate these GTPases to the level of cells expressing CD151. Small GTPases activated by engagement of CD151-β(1) integrin complexes contributed to CD151-induced cell motility and MMP-9 expression in human melanoma cells. Importantly, among the four tetraspanin proteins that associate with β(1) integrin, only CD151 exhibited the ability to facilitate complex formation between the β(1) family of integrins and small GTPases and stimulate β(1) integrin-dependent activation of small GTPases. These results suggest that CD151 links α(3)β(1)/α(6)β(1) integrins to Ras, Rac1, and Cdc42 by promoting the formation of multimolecular complexes in the membrane, which leads to the up-regulation of adhesion-dependent small GTPase activation.

Application of RNA-Seq transcriptome analysis: CD151 is an Invasion/Migration target in all stages of epithelial ovarian cancer

Background

RNA-Seq allows a theoretically unbiased analysis of both genome-wide transcription levels and mutation status of a tumor. Using this technique we sought to identify novel candidate therapeutic targets expressed in epithelial ovarian cancer (EOC).

Methods

Specifically, we sought candidate invasion/migration targets based on expression levels across all tumors, novelty of expression in EOC, and known function. RNA-Seq analysis revealed the high expression of CD151, a transmembrane protein, across all stages of EOC. Expression was confirmed at both the mRNA and protein levels using RT-PCR and immunohistochemical staining, respectively.

Results

In both EOC tumors and normal ovarian surface epithelial cells we demonstrated CD151 to be localized to the membrane and cell-cell junctions in patient-derived and established EOC cell lines. We next evaluated its role in EOC dissemination using two ovarian cancer-derived cell lines with differential levels of CD151 expression. Targeted antibody-mediated and siRNA inhibition or loss of CD151 in SKOV3 and OVCAR5 cell lines effectively inhibited their migration and invasion.

Conclusion

Taken together, these findings provide the first proof-of-principle demonstration for a next generation sequencing approach to identifying candidate therapeutic targets and reveal CD151 to play a role in EOC dissemination.

Hold tight or you'll fall off: CD151 helps podocytes stick in high-pressure situations

Glomerulosclerosis is a general term for scarring of the kidney glomerulus. It cannot be reversed. As glomerulosclerosis accumulates, the diseased kidney progresses to end-stage renal disease. Treatment with inhibitors of the renin-angiotensin system often decreases the rate of progression of glomerulosclerosis in chronic kidney diseases. Although the mechanisms by which these inhibitors mediate their beneficial effects are incompletely understood, it has been suggested that they act, at least in part, by reducing intraglomerular blood pressure and thereby shear stress-induced loss of podocytes, a key component of the glomerular filtration barrier. In this issue of the JCI, Sachs and colleagues provide experimental confirmation of the critical role of tight adhesion of podocytes to the glomerular basement membrane for maintaining glomerular integrity and provide evidence that inhibition of the renin-angiotensin system reduces glomerulosclerosis in animals with less tightly adherent podocytes, presumably by reducing intraglomerular blood pressure.

CD151 amplifies signaling by integrin α6β1 to PI3K and induces the epithelial-mesenchymal transition in HCC cells

BACKGROUND & AIMS

Overexpression of CD151 is associated with poor prognosis for hepatocellular carcinoma (HCC), yet its role in pathogenesis is not known.

METHODS

We analyzed the expression of the integrin subunit α6 by quantitative, real-time polymerase chain reaction and immunoblot analyses of 120 HCC tissue samples; its clinical significance was investigated using tissue microarray (TMAs) analysis of samples from 335 patients with HCC. Immunoprecipitation was used to assess the relationship between α6 and CD151. The molecular effects of high expression levels of α6 and CD151 in HCC cells were determined using RNA interference and pharmacologic approaches.

RESULTS

Overexpression of α6 correlated with poor prognosis of patients with HCC; α6 formed a complex with endogenous CD151 in HCC cells. In cells that expressed high levels of α6 and CD151, laminin-5 promoted cell spreading by inducing the epithelial-mesenchymal transition (EMT); this effect was not observed in cells that expressed high levels of only α6 or CD151. Cells that expressed high levels of α6 and CD151 underwent the EMT in response to laminin-5, through hyperactivation of phosphatidylinositol-3-kinase (PI3K), primarily induced via the PI3K-protein kinase B (Akt)-Snail-phosphatase and tensin homolog feedback pathway. The EMT was reversed by PI3K inhibitors and antibodies against CD151 or α6 in vitro, and was delayed by specific interference with CD151 and α6 in vivo.

CONCLUSIONS

High expression levels of CD151 and α6 promote invasiveness of HCC cells. Either of these proteins, or PI3K signaling, might be targets for therapeutics for subgroups of patients with HCC.

Tetraspanin, CD151, is required for maintenance of trigeminal placode identity

The trigeminal ganglion is the largest of the cranial ganglia and responsible for transmitting sensory information for much of the face. The cell surface glycoprotein CD151 is an early marker of the trigeminal placode, the precursor to the ganglion. Here, we investigate the role of CD151 during specification of trigeminal placode cells in the developing chicken embryo. Expression of the transcription factor Pax3, the earliest known marker of the trigeminal placode, briefly precedes that of CD151, but they then subsequently overlap in the trigeminal placode. Loss of CD151 protein dramatically decreases the number of Pax3+ placode cells in Stage 13-14 embryos, leading to loss of ophthalmic trigeminal neurons by Stages 16 and 17. Although the initial size of the Pax3 population is similar to that in controls, the number of Pax3+ cells decreases with time without alterations in cell death or proliferation. This suggests a role for CD151 in maintenance of the specification state in the trigeminal placode, uncovering the first known role for a tetraspanin in a developmental system.

Activation of the ERK signaling pathway is involved in CD151-induced angiogenic effects on the formation of CD151-integrin complexes

AIM

To assess the roles of extracellular signal-regulated kinase (ERK), p38, and CD151-integrin complexes on proliferation, migration, and tube formation activities of CD151-induced human umbilical vein endothelial cells (HUVECs).

METHODS

CD151, anti-CD151 and CD151-AAA mutant were inserted into recombinant adeno-associated virus (rAAV) vectors and used to transfect HUVECs. After transfection, the expression of CD151 was measured. Proliferation was assessed using the 3-[4,5-dimethylthiazol- 2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. Cell migration was evaluated in Boyden transwell chambers using FBS as the chemotactic stimulus. The tube formation assay was performed on matrigel. The potential involvement of various signaling pathways was explored using selective inhibitors.

RESULTS

CD151 gene delivery increased the expression of CD151 at both the mRNA and protein levels. Overexpression of CD151 promoted cell proliferation, migration and tube formation in vitro, and phosphorylation of ERK was also increased. Further, CD151-induced cell proliferation, migration, and tube formation were attenuated by the ERK inhibitor PD98059 (20 micromol/L) but not by a p38 inhibitor (SB203580, 20 micromol/L). Moreover, there was no significant difference in CD151 protein expression between the CD151 group and the CD151-AAA group, but the CD151-AAA mutant abrogated cellular proliferation, migration, and tube formation and decreased the phosphorylation of ERK.

CONCLUSION

This study suggests that activation of the ERK signaling pathway may be involved in the angiogenic effects of CD151. Activation of ERK was dependent on the formation of CD151-integrin complexes. Therefore modulation of CD151 may be as a novel therapeutic strategy for regulating angiogenesis.

Tetraspanin CD151 regulates growth of mammary epithelial cells in three-dimensional extracellular matrix: implication for mammary ductal carcinoma in situ

Tetraspanin CD151 is associated with laminin-binding integrins (i.e., alpha(3)beta(1), alpha(6)beta(1), and alpha(6)beta(4)) and regulates tumor cell migration and invasion. Here, we examined the role of CD151 in proliferation of mammary epithelial cells using in vitro and in vivo models. Depletion of CD151 suppressed growth of HB2 cells, a nontumorigenic breast epithelial cell line, in three-dimensional (3D) extracellular matrices (ECM) and in Matrigel-based xenografts. Whereas the presence of alpha(3)beta(1) (but not alpha(6) integrins) was necessary to support growth of HB2 cells in 3D ECM, the pro-proliferative activity of CD151 did not require direct interaction with integrins. Furthermore, depletion of CD151 potentiated formation of the internal lumen and partial restoration of polarity when HB2 cells were cultured in 3D ECM. This correlated with a decrease in phosphorylation levels of extracellular signal-regulated kinase 1/2 and cAkt in CD151-negative cells and increase in activation of caspase-3. Accordingly, the number of CD151-positive colonies with internal lumen was increased by approximately 5-fold when cells were cultured in the presence of MAP/ERK kinase (U0126) and phosphoinositide 3-kinase (LY29004) inhibitors. To establish the physiologic relevance of pro-proliferative and morphogenetic activities of CD151, we analyzed the expression of this tetraspanin in ductal carcinoma in situ (DCIS), which is characterized by neoplastic proliferation of mammary epithelial cells. Strong homogeneous membrane expression of CD151 was found to be associated with a high grade of DCIS (P = 0.004). Taken together, these results strongly suggest that CD151 complexes play a crucial role in the development of hyperproliferative diseases in the mammary gland.

Laminin-binding integrins and their tetraspanin partners as potential antimetastatic targets

Within the integrin family of cell adhesion receptors, integrins alpha3beta1, alpha6beta1, alpha6beta4 and alpha7beta1 make up a laminin-binding subfamily. The literature is divided on the role of these laminin-binding integrins in metastasis, with different studies indicating either pro- or antimetastatic functions. The opposing roles of the laminin-binding integrins in different settings might derive in part from their unusually robust associations with tetraspanin proteins. Tetraspanins organise integrins into multiprotein complexes within discrete plasma membrane domains termed tetraspanin-enriched microdomains (TEMs). TEM association is crucial to the strikingly rapid cell migration mediated by some of the laminin-binding integrins. However, emerging data suggest that laminin-binding integrins also promote the stability of E-cadherin-based cell-cell junctions, and that tetraspanins are essential for this function as well. Thus, TEM association endows the laminin-binding integrins with both pro-invasive functions (rapid migration) and anti-invasive functions (stable cell junctions), and the composition of TEMs in different cell types might help determine the balance between these opposing activities. Unravelling the tetraspanin control mechanisms that regulate laminin-binding integrins will help to define the settings where inhibiting the function of these integrins would be helpful rather than harmful, and may create opportunities to modulate integrin activity in more sophisticated ways than simple functional blockade.

Cell Adhesion Dynamics and Actin Cytoskeleton Reorganization in HepG2 Cell Aggregates

The temporal dependence of cytoskeletal remodelling on cell-cell contact in HepG2 cells has been established here. Cell-cell contact occurred in an ultrasound standing wave trap designed to form and levitate a 2-D cell aggregate, allowing intercellular adhesive interactions to proceed, free from the influences of solid substrata. Membrane spreading at the point of contact and change in cell circularity reached 50% of their final values within 2.2 min of contact. Junctional F-actin increased at the interface but lagged behind membrane spreading, reaching 50% of its final value in 4.4 min. Aggregates had good mechanical stability after 15 min in the trap. The implication of this temporal dependence on the sequential progress of adhesion processes is discussed. These results provide insight into how biomimetic cell aggregates with some liver cell functions might be assembled in a systematic, controlled manner in a 3-D ultrasound trap.

CD151 gene delivery after myocardial infarction promotes functional neovascularization and activates FAK signaling

Our previous studies showed that tetraspanin CD151 promotes neovascularization in rat hindlimb and myocardial ischemia models. This study is to assess whether CD151 induces arteriogenesis and promotes functional neovascularization in a pig myocardial infarction model, and to determine the signaling pathways involved. CD151 cDNA and antiCD151 sequence were constructed into a recombinant adeno-associated virus (rAAV) vector. All 26 pigs used either were subjected to coronary artery ligation or did not undergo surgery. Eight wks after viral administration, the expression of CD151 protein was measured by Western blot. The densities of capillaries and arterioles were determined using immunohistochemistry. Regional myocardial perfusion and other myocardial functions were evaluated by (13)N-labeled NH(3) positron emission computed tomography ((13)N-NH(3) PET) and echocardiography. Western blot was performed for assessing the signaling mechanisms. Overexpression of CD151 markedly increased the densities of capillaries and arterioles, significantly enhanced the regional myocardial perfusion, reduced myocardial ischemia, and improved the myocardial contraction, wall motion, and wall thickness. Conversely, antiCD151 gene delivery reversed the above changes. In addition, CD151 activated focal adhesion kinase (FAK), extracellular signal-regulated kinase (ERK), c-Jun N-teminal kinase (JNK), phosphatidylinositol-3 kinase (PI3K), protein kinase B (Akt), and endothelial nitric-oxide synthase (eNOS), and increased nitric oxide (NO) level. These findings demonstrate a robust role of CD151 in inducing and/or upregulating neovascularization. CD151-dependent neovascularization correlates with the activations of FAK, mitogen activated protein kinases (MAPKs), and PI3K signaling, suggesting that CD151 may promote neovascularization via MAPKs and PI3K pathways.

Tetraspanin CD151 regulates glycosylation of (alpha)3(beta)1 integrin

The tetraspanin CD151 forms a stoichiometric complex with integrin alpha3beta1 and regulates its endocytosis. We observed that down-regulation of CD151 in various epithelial cell lines changed glycosylation of alpha3beta1. In contrast, glycosylation of other transmembrane proteins, including those associated with CD151 (e.g. alpha6beta1, CD82, CD63, and emmprin/CD147) was not affected. The detailed analysis has shown that depletion of CD151 resulted in the reduction of Fucalpha1-2Gal and bisecting GlcNAc-beta(1-->4) linkage on N-glycans of the alpha3 integrin subunit. The modulatory activity of CD151 toward alpha3beta1 was specific, because stable knockdown of three other tetraspanins (i.e. CD9, CD63, and CD81) did not affect glycosylation of the integrin. Analysis of alpha3 glycosylation in CD151-depleted breast cancer cells with reconstituted expression of various CD151 mutants has shown that a direct contact with integrin is required but not sufficient for the modulatory activity of the tetraspanin toward alpha3beta1. We also found that glycosylation of CD151 is also critical; Asn(159) --> Gln mutation in the large extracellular loop did not affect interactions of CD151 with other tetraspanins or alpha3beta1 but negated its modulatory function. Changes in the glycosylation pattern of alpha3beta1 observed in CD151-depleted cells correlated with a dramatic decrease in cell migration toward laminin-332. Migration toward fibronectin or static adhesion of cells to extracellular matrix ligands was not affected. Importantly, reconstituted expression of the wild-type CD151 but not glycosylation-deficient mutant restored the migratory potential of the cells. These results demonstrate that CD151 plays an important role in post-translation modification of alpha3beta1 integrin and strongly suggest that changes in integrin glycosylation are critical for the promigratory activity of this tetraspanin.

Tetraspanins regulate ADAM10-mediated cleavage of TNF-alpha and epidermal growth factor

Several cytokines and growth factors are released by proteolytic cleavage of a membrane-anchored precursor, through the action of ADAM (a disintegrin and metalloprotease) metalloproteases. The activity of these proteases is regulated through largely unknown mechanisms. In this study we show that Ab engagement of several tetraspanins (CD9, CD81, CD82) increases epidermal growth factor and/or TNF-alpha secretion through a mechanism dependent on ADAM10. The effect of anti-tetraspanin mAb on TNF-alpha release is rapid, not relayed by intercellular signaling, and depends on an intact MEK/Erk1/2 pathway. It is also associated with a concentration of ADAM10 in tetraspanin-containing patches. We also show that a large fraction of ADAM10 associates with several tetraspanins, indicating that ADAM10 is a component of the "tetraspanin web." These data show that tetraspanins regulate the activity of ADAM10 toward several substrates, and illustrate how membrane compartmentalization by tetraspanins can control the function of cell surface proteins such as ectoproteases.

Tetraspanins affect myeloma cell fate via Akt signaling and FoxO activation

Myeloma cell interface with microenvironmental components is critical to cell growth and survival and perceived as a major obstacle for effective disease treatment. Hence, molecules that facilitate cell-cell and cell-ECM interactions are particularly important. We have previously shown that re-expression of membranal microdomain organizers, tetraspanins CD81 and CD82, caused myeloma cell death. Herein we demonstrate that the anti-myeloma effect of CD81/CD82 involves a down-regulation of Akt, activation of FoxO transcription factors and a decrease in active mTOR and mTOR/rictor. We go on to show in a breast cancer cell line model that Akt dependent cells are more sensitive to the tetraspanin overexpression. Moreover, expression of a constitutively active Akt increased survival of CD81/CD82 transfected myeloma cell lines. Akt and mTOR afford attractive therapeutic targets in cancer yet, due to pathways' interactions, inhibitors of mTOR frequently activate Akt and vise versa. Our results demonstrate co-repression of both by CD81/CD82 implying that tetraspanins may serve as "switches" modulating pathways rather than blocking a single factor and constitute a promising therapeutic strategy in Akt dependent pathological conditions. The possibility that the tetraspanins affect metabolic control is broached as well.

The inhibition of tumor cell intravasation and subsequent metastasis via regulation of in vivo tumor cell motility by the tetraspanin CD151

In vivo tumor cell migration through integrin-dependent pathways is key to the metastatic behavior of malignant cells. Using quantitative in vivo assays and intravital imaging, we assessed the impact of cell migration, regulated by the integrin-associated tetraspanin CD151, on spontaneous human tumor cell metastasis. We demonstrate that promoting immobility through a CD151-specific metastasis blocking mAb prevents tumor cell dissemination by inhibiting intravasation without affecting primary tumor growth, tumor cell arrest, extravasation, or growth at the secondary site. In vivo, this loss of migration is the result of enhanced tumor cell-matrix interactions, promoted by CD151, which prevent dissociation by individual cells and leads to a subsequent inhibition of invasion and intravasation at the site of the primary tumor.

The tumour-associated antigen L6 (L6-Ag) is recruited to the tetraspanin-enriched microdomains: implication for tumour cell motility

Tumour-associated antigen L6 (L6-Ag, also known as TM4SF1) regulates tumour cell motility and invasiveness. We found that L6-Ag is abundant on the plasma membrane and on intracellular vesicles, on which it is co-localised with the markers for late endosomal/lysosomal compartments, including Lamp1/Lamp2 proteins and LBPA. Antibody internalisation and live-imaging experiments suggested that L6-Ag is targeted to late endocytic organelles (LEO) predominantly via a biosynthetic pathway. Mapping experiments showed that the presence of transmembrane regions is sufficient for directing L6-Ag to LEO. On the plasma membrane, L6-Ag is associated with tetraspanin-enriched microdomains (TERM). All three predicted cytoplasmic regions of L6-Ag are crucial for the effective recruitment of the protein to TERM. Recruitment to TERM correlated with the pro-migratory activity of L6-Ag. Depletion of L6-Ag with siRNA has a selective effect on the surface expression of tetraspanins CD63 and CD82. By contrast, the expression levels of other tetraspanins and beta1 integrins was not affected. We found that L6-Ag is ubiquitylated and that ubiquitylation is essential for its function in cell migration. These data suggest that L6-Ag influences cell motility via TERM by regulating the surface presentation and endocytosis of some of their components.

Absence of CD9 enhances adhesion-dependent morphologic differentiation, survival, and matrix metalloproteinase-2 production in small cell lung cancer cells

While adhering to extracellular matrix proteins in vitro and in vivo, small cell lung cancer (SCLC) cells frequently show morphologic differentiation and are protected from apoptosis. Integrin beta(1)-mediated protein phosphorylation is suggested to be an essential signaling event in these processes. CD9 is an almost ubiquitously expressed tetraspanin protein that suppresses tumor progression by regulating cell motility and signaling through complex formation with beta(1) integrins. We reported previously that, among tetraspanins, CD9 is selectively absent in most SCLC cells and that ectopic expression of CD9 suppresses their motility. Here, we show that the ectopic expression of CD9 suppressed neurite-like process outgrowth and promoted apoptotic death of SCLC cells that were adherent to fibronectin in serum-starved conditions. This correlated with attenuation of adhesion-dependent phosphorylation of Akt but not that of focal adhesion kinase or c-Jun NH(2)-terminal kinase. Treatment of CD9(-) parent cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, inhibited process outgrowth and survival, suggesting that PI3K/Akt signaling is required for the morphologic change and cell survival. Production of matrix metalloproteinase (MMP)-2 was likewise suppressed in the CD9 transfectants and in LY294002-treated parent cells. These results suggest that the absence of CD9 in SCLC cells may contribute to postadhesive morphologic differentiation, survival, and MMP-2 production via PI3K/Akt pathway.

Tetraspanin CD151 promotes cell migration by regulating integrin trafficking

Regulation of cell migration is an important feature of tetraspanin CD151. Although it is well established that CD151 physically associates with integrins, the mechanism by which CD151 regulates integrin-dependent cell migration is basically unknown. Given the fact that CD151 is localized in both the plasma membrane and intracellular vesicles, we found that CD151 and its associated alpha3beta1, alpha5beta1, and alpha6beta1 integrins undergo endocytosis and accumulate in the same intracellular vesicular compartments. CD151 contains a YRSL sequence, a YXXvarphi type of endocytosis/sorting motif, in its C-terminal cytoplasmic domain. Mutation of this motif markedly attenuated CD151 internalization. The loss of CD151 trafficking completely abrogated CD151-promoted cell migration on extracellular matrices such as laminin and diminished the internalization of its associated integrins, indicating a critical role for integrin trafficking in regulating cell motility. In conclusion, the YXXvarphi motif-mediated internalization of CD151 promotes integrin-dependent cell migration by modulating the endocytosis and/or vesicular trafficking of its associated integrins.

Activation of the phosphatidylinositol 3-kinase/protein kinase Akt pathway mediates CD151-induced endothelial cell proliferation and cell migration

We previously reported that CD151 promotes neovascularization and improves blood perfusion in rat hind-limb ischemia model, but the precise mechanism is still unclear. Endothelial cell proliferation and cell migration play critical roles in angiogenesis. Many growth factors and hormones have been shown to regulate cell proliferation, cell migration and angiogenesis, including the activation of eNOS activity, via the PI3K/Akt signaling pathway. Whether CD151 induces cell proliferation and cell migration via PI3K/Akt signaling pathway is not known. Here we showed that CD151 promotes human umbilical vein endothelial cell (HUVEC) proliferation, migration and tube formation in vitro, accompanied by increased phosphorylation of Akt and eNOS, leading to increased eNOS activity and nitric oxide (NO) levels after rAAV-CD151 infection, whereas infection with rAAV-anti-CD151 attenuated the effects of CD151, which suggested that CD151 can activate PI3K/Akt pathway. Moreover, inhibitors of PI3K (LY294002) and eNOS (l-NAME) can attenuate CD151-induced cell proliferation and cell migration. The results suggested that activation of PI3K/Akt signaling pathway mediates CD151-induced cell proliferation and migration.

Homophilic interactions of Tetraspanin CD151 up-regulate motility and matrix metalloproteinase-9 expression of human melanoma cells through adhesion-dependent c-Jun activation signaling pathways

The tetraspanin membrane protein CD151 has been suggested to regulate cancer invasion and metastasis by initiating signaling events. The CD151-mediated signaling pathways involved in this regulation remain to be revealed. In this study, we found that stable transfection of CD151 into MelJuSo human melanoma cells lacking CD151 expression significantly increased cell motility, matrix metalloproteinase-9 (MMP-9) expression, and invasiveness. The enhancement of cell motility and MMP-9 expression by CD151 overexpression was abrogated by inhibitors and small interfering RNAs targeted to focal adhesion kinase (FAK), Src, p38 MAPK, and JNK, suggesting an essential role of these signaling components in CD151 signaling pathways. Also, CD151-induced MMP-9 expression was shown to be mediated by c-Jun binding to AP-1 sites in the MMP-9 gene promoter, indicating AP-1 activation by CD151 signaling pathways. Meanwhile, CD151 was found to be associated with alpha(3)beta(1) and alpha(6)beta(1) integrins in MelJuSo cells, and activation of associated integrins was a prerequisite for CD151-stimulated MMP-9 expression and activation of FAK, Src, p38 MAPK, JNK, and c-Jun. Furthermore, CD151 on one cell was shown to bind to neighboring cells expressing CD151, suggesting that CD151 is a homophilic interacting protein. The homophilic interactions of CD151 increased motility and MMP-9 expression of CD151-transfected MelJuSo cells, along with FAK-, Src-, p38 MAPK-, and JNK-mediated activation of c-Jun in an adhesion-dependent manner. Furthermore, C8161 melanoma cells with endogenous CD151 were also shown to respond to homophilic CD151 interactions for the induction of adhesion-dependent activation of FAK, Src, and c-Jun. These results suggest that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through FAK-Src-MAPKs pathways in human melanoma cells, leading to enhanced cell motility and MMP-9 expression.

Wound healing is defective in mice lacking tetraspanin CD151

The tetraspanin CD151 forms complexes in epithelial cell membranes with laminin-binding integrins alpha6beta4, alpha3beta1, and alpha6beta1, and modifies integrin-mediated cell migration in vitro. We demonstrate in this study that CD151 expression is upregulated in a distinct temporal and spatial pattern during wound healing, particularly in the migrating epidermal tongue at the wound edge, suggesting a role for CD151 in keratinocyte migration. We show that healing is significantly impaired in CD151-null mice, with wounds gaping wider at 7 days post-injury. The rate of re-epithelialization of the CD151-null wounds is adversely affected, with significantly less wound area being covered by migrating epidermal cells. Our studies reveal that although laminin levels are similar in wild-type and CD151-null wounds, the organization of the laminin in the basement membrane is impaired. Furthermore, upregulation of alpha6 and beta4 integrin expression is adversely affected in CD151-null mice wounds. In contrast, we find no significant effect of CD151 gene knockout on alpha3 and beta1 integrin expression in wound repair. We suggest that mice lacking the CD151 gene are defective in wound healing, primarily owing to impairment of the re-epithelialization process. This may be due to defective basement membrane formation and epithelial cell adhesion and migration.

Predicted and measured disorder in peripherin/rds, a retinal tetraspanin

Vertebrate photoreceptor outer segment (OS) morphogenesis requires peripherin/rds (P/rds). We have characterized this protein's C-terminus and present evidence that suggests it is intrinsically disordered. We propose that structural flexibility may underlie the multifunctionality proposed for this domain previously. The extremely short C-termini present in other tetraspanin family members suggest that intrinsic disorder may also play a role for those proteins.

Tetraspanin functions and associated microdomains

Cell-surface proteins of the tetraspanin family are small, and often hidden by a canopy of tall glycoprotein neighbours in the cell membrane. Consequently, tetraspanins have been understudied and underappreciated, despite their presence on nearly all cell and tissue types. Important new genetic evidence has now emerged, and is bolstered by new insights into the cell biology, signalling and biochemistry of tetraspanins. These new findings provide a framework for better understanding of these mysterious molecules in the regulation of cellular processes, from signalling to motility.

Down-regulation of CD9 in human ovarian carcinoma cell might contribute to peritoneal dissemination: morphologic alteration and reduced expression of beta1 integrin subsets

Peritoneal dissemination is one of the main causes of death in cancer patients. Pathophysiology of metastasis has been well investigated, but the mechanism of diffuse spread of tumor colonies in the peritoneal cavity is not fully understood. CD9 is a member of tetraspanin and its down-regulation is known to be involved in poor prognosis. To investigate the significance of the down-regulation of CD9, HTOA, an ovarian carcinoma cell line that highly expressed CD9, was transiently transfected with small interfering RNA (siRNA) against CD9, and CD9-negative cells (HTOA(CD9-)) were purified. HTOA(CD9-) showed altered adhesion patterns on Matrigel, collagen, fibronectin, and laminin compared with those of control siRNA-transfected HTOA (control-HTOA). Flow cytometry and fluorescence cytostainings revealed that the expression levels of integrins beta1, alpha2, alpha3beta1, alpha5, and alpha6 were lower in HTOA(CD9-) than those of control-HTOA. HTOA(CD9-) showed altered expression of junctional and cytoskeletal molecules. By time-lapse video microscopy, control-HTOA showed solid adhesion to extracellular matrix and formed cobblestone pattern, whereas HTOA(CD9-) showed weaker adhesion and were distributed as diffuse spots. To examine whether the expression level of CD9 change during tumor dissemination, HTOA-P, a highly disseminative subclone of HTOA, was established. HTOA-P showed distinctive down-regulation of CD9 at mRNA and protein levels, and showed similar morphologic alteration as HTOA(CD9-) did. These findings indicate that the down-regulation of CD9 may be an acquired event in the process of tumor dissemination. Down-regulated CD9 may attenuate the expression of several integrins and rearrange junctional and cytoskeletal molecules that might contribute to dissemination of ovarian carcinomas.

Increased expression of Drosophila tetraspanin, Tsp68C, suppresses the abnormal proliferation of ytr-deficient and Ras/Raf-activated hemocytes

Tetraspanins are evolutionary conserved transmembrane proteins thought to facilitate cell proliferation, movement or fusion by acting as organizers of different signaling events. Despite their prevalence and conservation, their specific role and functions remain largely elusive, as their redundancy in various organisms has hindered loss of function studies. Here, we take a gain of function approach to study Drosophila tetraspanin Tsp68C and its effect on larval hemocytes. We recently characterized a lethal mutation in ytr, a conserved gene that encodes a nuclear arginine-rich protein of unknown function, which is accompanied by abnormal differentiation and proliferation of the larval hematopoietic tissue in flies. A hemolectin (hml)-Gal4 construct carried by hml-Gal4 transgenic flies was sufficient by itself to abrogate the hematopoietic defects in ytr mutant larvae. This rescue correlated with the overexpression of tsp68C, a tetraspanin gene nested in the hml promoter. The suppression of abnormal proliferation by the hml-Gal4 construct was not restricted to ytr-deficient hemocytes, but was also observed in hemocytes expressing the oncogenic forms of Raf or Ras proteins. However, it had no effect on overproliferation mediated by a constitutively active form of Jak. New hml-Gal4 lines, in which the tsp68C gene was silenced or deleted from the promoter, no longer rescued the hematopoietic defect in ytr mutants nor suppressed the activated Raf-induced overproliferation. Therefore, change in tetraspanin Tsp68C expression has a strong suppressor effect on abnormal proliferation and differentiation of hemocytes in the context of specific lesions, such as overactivation of the Ras/Raf/MAPK pathway.

Regulation of urokinase receptor proteolytic function by the tetraspanin CD82

The high affinity interaction between the urokinase-type plasminogen activator (uPA) and its glycolipid-anchored cellular receptor (uPAR) promotes plasminogen activation and the efficient generation of pericellular proteolytic activity. We demonstrate here that expression of the tetraspanin CD82/KAI1 (a tumor metastasis suppressor) leads to a profound effect on uPAR function. Pericellular plasminogen activation was reduced by approximately 50-fold in the presence of CD82, although levels of components of the plasminogen activation system were unchanged. uPAR was present on the cell surface and molecularly intact, but radioligand binding analysis with uPA and anti-uPAR antibodies revealed that it was in a previously undetected cryptic form unable to bind uPA. This was not due to direct interactions between uPAR and CD82, as they neither co-localized on the cell surface nor could be co-immunoprecipitated. However, expression of CD82 led to a redistribution of uPAR to focal adhesions, where it was shown by double immunofluorescence labeling to co-localize with the integrin alpha(5)beta(1), which was also redistributed in the presence of CD82. Co-immunoprecipitation experiments showed that, in the presence of CD82, uPAR preferentially formed stable associations with alpha(5)beta(1), but not with a variety of other integrins, including alpha(3)beta(1). These data suggest that CD82 inhibits the proteolytic function of uPAR indirectly, directing uPAR and alpha(5)beta(1) to focal adhesions and promoting their association with a resultant loss of uPA binding. This represents a novel mechanism whereby tetraspanins, integrins, and uPAR, systems involved in cell adhesion and migration, cooperate to regulate pericellular proteolytic activity and may suggest a mechanism for the tumor-suppressive effects of CD82/KAI1.

Global and distinct targets of IRF-5 and IRF-7 during innate response to viral infection

The interferon regulatory factors (IRF) are transcriptional mediators of cellular response to viral invasion that play a critical role in the innate antiviral defense. Two of these factors, IRF-5 and IRF-7, play a critical role in the induction of interferon (IFNA) genes in infected cells; they are expressed constitutively in monocytes, B cells, and precursors of dendritic cells (pDC2) that are high producers of interferon alpha, and their expression can be further stimulated by type I interferon. The goal of the present study was to identify and analyze expression of cellular genes that are modulated by IRF-5 and IRF-7 during the innate response to viral infection. The transcription profiles of infected BJAB cells overexpressing IRF-5 or IRF-7 were determined by using oligonucleotide arrays with probe sets representing about 6800 human genes. This analysis shows that IRF-5 and IRF-7 activate a broad profile of heterologous genes encoding not only antiviral, inflammatory, and pro-apoptotic proteins but also proteins of other functional categories. The number of IRF-5- and IRF-7-modulated genes was significantly higher in infected than in uninfected cells, and the transcription signature was predominantly positive. Although IRF-5 and IRF-7 stimulated a large number of common genes, a distinct functional profile was associated with each of these IRFs. The noted difference was a broad antiviral and early inflammatory transcriptional profile in infected BJAB/IRF-5 cells, whereas the IRF-7-induced transcripts were enriched for the group of mitochondrial genes and genes affecting the DNA structure. Taken together, these data indicate that IRF-5 and IRF-7 act primarily as transcriptional activators and that IRF-5-and IRF-7-induced innate antiviral response results in a broad alteration of the transcriptional profile of cellular genes.

Characterization of mice lacking the tetraspanin superfamily member CD151

The tetraspanin membrane protein CD151 is a broadly expressed molecule noted for its strong molecular associations with integrins, especially alpha3beta1, alpha6beta1, alpha7beta1, and alpha6beta4. In vitro functional studies have pointed to a role for CD151 in cell-cell adhesion, cell migration, platelet aggregation, and angiogenesis. It has also been implicated in epithelial tumor progression and metastasis. Here we describe the generation and initial characterization of CD151-null mice. The mice are viable, healthy, and fertile and show normal Mendelian inheritance. They have essentially normal blood and bone marrow cell counts and grossly normal tissue morphology, including hemidesmosomes in skin, and expression of alpha3 and alpha6 integrins. However, the CD151-null mice do show phenotypes in several different tissue types. An absence of CD151 leads to a minor abnormality in hemostasis, with CD151-null mice showing longer average bleeding times, greater average blood loss, and an increased incidence of rebleeding occurrences. CD151-null keratinocytes migrate poorly in skin explant cultures. Finally, CD151-null T lymphocytes are hyperproliferative in response to in vitro mitogenic stimulation.