Controlling cell surface dynamics and signaling: how CD82/KAI1 suppresses metastasis

A Potential Role of CD82/KAI1 during Uterine Decidualization in Mice

The tumor metastasis suppressor gene CD82/KAI1 has been demonstrated to impact human trophoblast invasion and migration. Communication between trophoblasts and decidual stromal cells plays a crucial role in controlling the normal invasiveness of trophoblasts. However, whether CD82/KAI1 is involved in decidualization and what role it plays remain unclear. CD82/KAI1 demonstrates specific spatiotemporal expression patterns in stromal cells undergoing decidualization during pregnancy. This is observed in both naturally pregnant females post-implantation and pseudopregnant mice undergoing induced decidualization, as detected through in situ hybridization and immunofluorescence. CD82/KAI1 expression showed a significant time-dependent increase in cultured stromal cells after 24 and 48 h of progesterone (P4) and estrogen (E2) treatment. This was accompanied by a notable upregulation of decidualization markers, including cyclin D3 and PR. After transducing stromal cells with the adenovirus-overexpressing CD82/KAI1 for 48 h, the expression of cyclin D3 protein increased. Meanwhile, there was an attenuated expression of CD82/KAI1 due to an adenovirus siRNA knockdown, whereas cyclin D3 and PR expressions were not affected. Our findings suggest a potential role of CD82/KAI1 in regulating the process of decidualization, providing insights into stromal cell differentiation.

Tetraspanin CD82 Correlates with and May Regulate S100A7 Expression in Oral Cancer

Many metastatic cancers with poor prognoses correlate to downregulated CD82, but exceptions exist. Understanding the context of this correlation is essential to CD82 as a prognostic biomarker and therapeutic target. Oral squamous cell carcinoma (OSCC) constitutes over 90% of oral cancer. We aimed to uncover the function and mechanism of CD82 in OSCC. We investigated CD82 in human OSCC cell lines, tissues, and healthy controls using the CRISPR-Cas9 gene knockout, transcriptomics, proteomics, etc. CD82 expression is elevated in CAL 27 cells. Knockout CD82 altered over 300 genes and proteins and inhibited cell migration. Furthermore, CD82 expression correlates with S100 proteins in CAL 27, CD82KO, SCC-25, and S-G cells and some OSCC tissues. The 37-50 kDa CD82 protein in CAL 27 cells is upregulated, glycosylated, and truncated. CD82 correlates with S100 proteins and may regulate their expression and cell migration. The truncated CD82 explains the invasive metastasis and poor outcome of the CAL 27 donor. OSCC with upregulated truncated CD82 and S100A7 may represent a distinct subtype with a poor prognosis. Differing alternatives from wild-type CD82 may elucidate the contradictory functions and pave the way for CD82 as a prognostic biomarker and therapeutic target.

Tetraspanin CD82 Associates with Trafficking Vesicle in Muscle Cells and Binds to Dysferlin and Myoferlin

Tetraspanins organize protein complexes at the cell membrane and are responsible for assembling diverse binding partners in changing cellular states. Tetraspanin CD82 is a useful cell surface marker for prospective isolation of human myogenic progenitors and its expression is decreased in Duchenne muscular dystrophy (DMD) cell lines. The function of CD82 in skeletal muscle remains elusive, partly because the binding partners of this tetraspanin in muscle cells have not been identified. CD82-associated proteins are sought to be identified in human myotubes via mass spectrometry proteomics, which identifies dysferlin and myoferlin as CD82-binding partners. In human dysferlinopathy (Limb girdle muscular dystrophy R2, LGMDR2) myogenic cell lines, expression of CD82 protein is near absent in two of four patient samples. In the cell lines where CD82 protein levels are unaffected, increased expression of the ≈72 kDa mini-dysferlin product is identified using an antibody recognizing the dysferlin C-terminus. These data demonstrate that CD82 binds dysferlin/myoferlin in differentiating muscle cells and its expression can be affected by loss of dysferlin in human myogenic cells.

The maintenance mechanism of hematopoietic stem cell dormancy: role for a subset of macrophages

Hematopoiesis is regulated by crosstalk between long-term repopulating hematopoietic stem cells (LT-HSCs) and supporting niche cells in the bone marrow (BM). Here, we describe the role of KAI1, which is mainly expressed on LT-HSCs and rarely on other hematopoietic stem-progenitor cells (HSPCs), in nichemediated LT-HSC maintenance. KAI1 activates TGF-β1/Smad3 signal in LT-HSCs, leading to the induction of CDK inhibitors and inhibition of the cell cycle. The KAI1-binding partner DARC is expressed on macrophages and stabilizes KAI1 on LT-HSCs, promoting their quiescence. Conversely, when DARC+ BM macrophages were absent, the level of surface KAI1 on LT-HSCs decreases, leading to cell-cycle entry, proliferation, and differentiation. Thus, KAI1 acts as a functional surface marker of LTHSCs that regulates dormancy through interaction with DARCexpressing macrophages in the BM stem cell niche. Recently, we showed very special and rare macrophages expressing α-SMA+ COX2+ & DARC+ induce not only dormancy of LTHSC through interaction of KAI1-DARC but also protect HSCs by down-regulating ROS through COX2 signaling. In the near future, the strategy to combine KAI1-positive LT-HSCs and α-SMA/Cox2/DARC triple-positive macrophages will improve the efficacy of stem cell transplantation after the ablative chemo-therapy for hematological disorders including leukemia. [BMB Reports 2023; 56(9): 482-487].

Liprin-α1 Expression in Tumor-Infiltrating Lymphocytes Associates with Improved Survival in Patients with HPV-Positive Oropharyngeal Squamous Cell Carcinoma

BACKGROUND

Liprin-α1 is a scaffold protein involved in cell adhesion, motility, and invasion in malignancies. Liprin-α1 inhibits the expression of metastatic suppressor CD82 in cancers such as oral carcinoma, and the expression of these proteins has been known to correlate negatively. The role of these proteins has not been previously studied in human papillomavirus (HPV)-related head and neck cancers. Our aim was to assess the clinical and prognostic role of liprin-α1 and CD82 in HPV-positive oropharyngeal squamous cell carcinoma (OPSCC) in comparison to HPV-negative OPSCC.

METHODS

The data included 139 OPSCC patients treated at the Helsinki University Hospital (HUS) during 2012-2016. Immunohistochemistry was utilized in HPV determination and in biomarker assays. Overall survival (OS) was used in the survival analysis.

RESULTS

Stronger expression of liprin-α1 in tumor-infiltrating lymphocytes (TILs) was linked to lower cancer stage (p < 0.001) and HPV positivity (p < 0.001). Additionally, we found an association between elevated expression of liprin-α1 and weak expression of CD82 in tumor cells (p = 0.029). In survival analysis, we found significant correlation between favorable OS and stronger expression of liprin-α1 in TILs among the whole patient cohort (p < 0.001) and among HPV-positive patients (p = 0.042).

CONCLUSIONS

Increased liprin-α1 expression in the TILs is associated with favorable prognosis in OPSCC, especially among HPV-positive patients.

Inhibition of CD82 improves colitis by increasing NLRP3 deubiquitination by BRCC3

CD82 is a transmembrane protein that is involved in cancer suppression and activates immune cells; however, information on the NLRP3 inflammasome is limited. Herein, we show that although CD82 suppressed the activation of the NLRP3 inflammasome in vivo and in vitro, CD82 deficiency decreased the severity of colitis in mice. Furthermore, two binding partners of CD82, NLRP3 and BRCC3, were identified. CD82 binding to these partners increased the degradation of NLRP3 by blocking BRCC3-dependent K63-specific deubiquitination. Previous studies have shown that CD82-specific bacteria in the colon microbiota called Bacteroides vulgatus (B. vulgatus) regulated the expression of CD82 and promoted the activation of the NLRP3 inflammasome. Accordingly, we observed that B. vulgatus administration increased mouse survival by mediating CD82 expression and activating NLRP3 in mice with colitis. Overall, this study showed that CD82 suppression reduced the pathogenesis of colitis by elevating the activation of the NLRP3 inflammasome through BRCC3-dependent K63 deubiquitination. Based on our findings, we propose that B. vulgatus is a novel therapeutic candidate for colitis.

Expression of KAI1 and AGR2 in lung adenocarcinoma and their clinicopathological significance

OBJECTIVE

Anticancer 1 (KAI1, tumor metastasis suppressor gene) and Anterior gradient-2 (AGR2, considered a valuable prognostic factor for some cancers) are associated with metastasis and prognosis of various types of human cancers. Nevertheless, the relationship between KAI1 and AGR2 in lung adenocarcinoma (LUAD) remains unclear. In this research, we analyzed the correlations between KAI1 and AGR2 in LUAD, and explored their correlations with clinicopathological parameters and overall survival time (OS) in patients with LUAD.

METHODS

Immunohistochemical staining was used to detect KAI1 and AGR2 expression in 132 cases of LUAD samples. At the same time, all clinicopathological parameters and postoperative survival information were collected.

RESULTS

AGR2 positive rate was significantly increased and KAI1 positive rate was significantly decreased in LUAD and control tissues. KAI1 positive rates were negatively correlated with tumor stage, LNM stage and TNM stage, and KAI1 subgroup positive expression of OS was significantly higher than negative KAI1 subgroup. The positive rate of AGR2 was positively correlated with tumor grade, LNM stage and TNM stage, and negatively correlated with patients OS. Active expression of AGR2 and KAI1, tumor stage, and LNM stage in multivariate analyses may be independent prognostic factors for OS in LUAD patients.

CONCLUSION

KAI1 and AGR2 may be potential biomarkers for prognosis and metastasis, and they are also promising therapeutic targets for LUAD patients.

The DARC Side of Inflamm-Aging: Duffy Antigen Receptor for Chemokines (DARC/ACKR1) as a Potential Biomarker of Aging, Immunosenescence, and Breast Oncogenesis among High-Risk Subpopulations

The proclivity of certain pre-malignant and pre-invasive breast lesions to progress while others do not continues to perplex clinicians. Clinicians remain at a crossroads with effectively managing the high-risk patient subpopulation owing to the paucity of biomarkers that can adequately risk-stratify and inform clinical decisions that circumvent unnecessary administration of cytotoxic and invasive treatments. The immune system mounts the most important line of defense against tumorigenesis and progression. Unfortunately, this defense declines or "ages" over time-a phenomenon known as immunosenescence. This results in "inflamm-aging" or the excessive infiltration of pro-inflammatory chemokines, which alters the leukocyte composition of the tissue microenvironment, and concomitant immunoediting of these leukocytes to diminish their antitumor immune functions. Collectively, these effects can foster the sequelae of neoplastic transformation and progression. The erythrocyte cell antigen, Duffy antigen receptor for chemokines(DARC/ACKR1), binds and internalizes chemokines to maintain homeostatic levels and modulate leukocyte trafficking. A negative DARC status is highly prevalent among subpopulations of West African genetic ancestry, who are at higher risk of developing breast cancer and disease progression at a younger age. However, the role of DARC in accelerated inflamm-aging and malignant transformation remains underexplored. Herein, we review compelling evidence suggesting that DARC may be protective against inflamm-aging and, therefore, reduce the risk of a high-risk lesion progressing to malignancy. We also discuss evidence supporting that immunotherapeutic intervention-based on DARC status-among high-risk subpopulations may evade malignant transformation and progression. A closer look into this unique role of DARC could glean deeper insight into the immune response profile of individual high-risk patients and their predisposition to progress as well as guide the administration of more "cyto-friendly" immunotherapeutic intervention to potentially "turn back the clock" on inflamm-aging-mediated oncogenesis and progression.

KAI1(CD82) is a key molecule to control angiogenesis and switch angiogenic milieu to quiescent state

BACKGROUND

Little is known about endogenous inhibitors of angiogenic growth factors. In this study, we identified a novel endogenous anti-angiogenic factor expressed in pericytes and clarified its underlying mechanism and clinical significance.

METHODS

Herein, we found Kai1 knockout mice showed significantly enhanced angiogenesis. Then, we investigated the anti-angiogenic roll of Kai1 in vitro and in vivo.

RESULTS

KAI1 was mainly expressed in pericytes rather than in endothelial cells. It localized at the membrane surface after palmitoylation by zDHHC4 enzyme and induced LIF through the Src/p53 pathway. LIF released from pericytes in turn suppressed angiogenic factors in endothelial cells as well as in pericytes themselves, leading to inhibition of angiogenesis. Interestingly, KAI1 had another mechanism to inhibit angiogenesis: It directly bound to VEGF and PDGF and inhibited activation of their receptors. In the two different in vivo cancer models, KAI1 supplementation significantly inhibited tumor angiogenesis and growth. A peptide derived from the large extracellular loop of KAI1 has been shown to have anti-angiogenic effects to block the progression of breast cancer and retinal neovascularization in vivo.

CONCLUSIONS

KAI1 from PC is a novel molecular regulator that counterbalances the effect of angiogenic factors.

CD82 and Gangliosides Tune CD81 Membrane Behavior

Tetraspanins are a family of transmembrane proteins that form a network of protein–protein interactions within the plasma membrane. Within this network, tetraspanin are thought to control the lateral segregation of their partners at the plasma membrane through mechanisms involving specific lipids. Here, we used a single molecule tracking approach to study the membrane behavior of tetraspanins in mammary epithelial cells and demonstrate that despite a common overall behavior, each tetraspanin (CD9, CD81 and CD82) has a specific signature in terms of dynamics. Furthermore, we demonstrated that tetraspanin dynamics on the cell surface are dependent on gangliosides. More specifically, we found that CD82 expression increases the dynamics of CD81 and alters its localization at the plasma membrane, this has no effect on the behavior of CD9. Our results provide new information on the ability of CD82 and gangliosides to differentially modulate the dynamics and organization of tetraspanins at the plasma membrane and highlight that its lipid and protein composition is involved in the dynamical architecture of the tetraspanin web. We predict that CD82 may act as a regulator of the lateral segregation of specific tetraspanins at the plasma membrane while gangliosides could play a crucial role in establishing tetraspanin-enriched areas.

Gene expression analysis of human prostate cell lines with and without tumor metastasis suppressor CD82

BACKGROUND

Tetraspanin CD82 is a tumor metastasis suppressor that is known to down regulate in various metastatic cancers. However, the exact mechanism by which CD82 prevents cancer metastasis is unclear. This study aims to identify genes that are regulated by CD82 in human prostate cell lines.

METHODS

We used whole human genome microarray to obtain gene expression profiles in a normal prostate epithelial cell line that expressed CD82 (PrEC-31) and a metastatic prostate cell line that does not express CD82 (PC3). Then, siRNA silencing was used to knock down CD82 expression in PrEC-31 while CD82 was re-expressed in PC3 to acquire differentially-expressed genes in the respective cell line.

RESULTS

Differentially-expressed genes with a P < 0.05 were identified in 3 data sets: PrEC-31 (+CD82) vs PrEC-31(-CD82), PC3-57 (+CD82) vs. PC3-5 V (-CD82), and PC3-29 (+CD82) vs. PC3-5 V (-CD82). Top 25 gene lists did not show overlap within the data sets, except (CALB1) the calcium binding protein calbindin 1 which was significantly up-regulated (2.8 log fold change) in PrEC-31 and PC3-29 cells that expressed CD82. Other most significantly up-regulated genes included serine peptidase inhibitor kazal type 1 (SPINK1) and polypeptide N-acetyl galactosaminyl transferase 14 (GALNT14) and most down-regulated genes included C-X-C motif chemokine ligand 14 (CXCL14), urotensin 2 (UTS2D), and fibroblast growth factor 13 (FGF13). Pathways related with cell proliferation and angiogenesis, migration and invasion, cell death, cell cycle, signal transduction, and metabolism were highly enriched in cells that lack CD82 expression. Expression of two mutually inclusive genes in top 100 gene lists of all data sets, runt-related transcription factor (RUNX3) and trefoil factor 3 (TFF3), could be validated with qRT-PCR.

CONCLUSION

Identification of genes and pathways regulated by CD82 in this study may provide additional insights into the role that CD82 plays in prostate tumor progression and metastasis, as well as identify potential targets for therapeutic intervention.

Tetraspanin CD82 is necessary for muscle stem cell activation and supports dystrophic muscle function

Background

Tetraspanins are a family of proteins known to assemble protein complexes at the cell membrane. They are thought to play diverse cellular functions in tissues by modifying protein-binding partners, thus bringing complexity and diversity in their regulatory networks. Previously, we identified the tetraspanin KAI/CD82 as a prospective marker for human muscle stem cells. CD82 expression appeared decreased in human Duchenne muscular dystrophy (DMD) muscle, suggesting a functional link to muscular dystrophy, yet whether this decrease is a consequence of dystrophic pathology or a compensatory mechanism in an attempt to rescue muscle from degeneration is currently unknown.

Methods

We studied the consequences of loss of CD82 expression in normal and dystrophic skeletal muscle and examined the dysregulation of downstream functions in mice aged up to 1 year.

Results

Expression of CD82 is important to sustain satellite cell activation, as in its absence there is decreased cell proliferation and less efficient repair of injured muscle. Loss of CD82 in dystrophic muscle leads to a worsened phenotype compared to control dystrophic mice, with decreased pulmonary function, myofiber size, and muscle strength. Mechanistically, decreased myofiber size in CD82^−/− dystrophic mice is not due to altered PTEN/AKT signaling, although increased phosphorylation of mTOR at Ser2448 was observed.

Conclusion

Basal CD82 expression is important to dystrophic muscle, as its loss leads to significantly weakened myofibers and impaired muscle function, accompanied by decreased satellite cell activity that is unable to protect and repair myofiber damage.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-020-00252-3.

Tetraspanin CD82 drives acute myeloid leukemia chemoresistance by modulating protein kinase C alpha and β1 integrin activation

A principal challenge in treating acute myeloid leukemia (AML) is chemotherapy refractory disease. As such, there remains a critical need to identify key regulators of chemotherapy resistance in AML. In this study, we demonstrate that the membrane scaffold, CD82, contributes to the chemoresistant phenotype of AML. Using an RNA-seq approach, we identified the increased expression of the tetraspanin family member, CD82, in response to the chemotherapeutic, daunorubicin. Analysis of the TARGET and BEAT AML databases identifies a correlation between CD82 expression and overall survival of AML patients. Moreover, using a combination of cell lines and patient samples, we find that CD82 overexpression results in significantly reduced cell death in response to chemotherapy. Investigation of the mechanism by which CD82 promotes AML survival in response to chemotherapy identified a crucial role for enhanced protein kinase c alpha (PKCα) signaling and downstream activation of the β1 integrin. In addition, analysis of β1 integrin clustering by super-resolution imaging demonstrates that CD82 expression promotes the formation of dense β1 integrin membrane clusters. Lastly, evaluation of survival signaling following daunorubicin treatment identified robust activation of p38 mitogen-activated protein kinase (MAPK) downstream of PKCα and β1 integrin signaling when CD82 is overexpressed. Together, these data propose a mechanism where CD82 promotes chemoresistance by increasing PKCα activation and downstream activation/clustering of β1 integrin, leading to AML cell survival via activation of p38 MAPK. These observations suggest that the CD82-PKCα signaling axis may be a potential therapeutic target for attenuating chemoresistance signaling in AML.

The expression of ubiquitin-conjugating enzyme E2C and KAI1 in ovarian carcinoma and their clinical significance

Ubiquitin-conjugating enzyme E2C (UBE2C) is considered to play an important role in the tumorigenesis of many cancers and promote cell cycle progression. Kangai 1 (KAI1) is considered as a suppressor gene of tumor metastasis. However, the clinicopathological significance and their each relationship of UBE2C and KAI1 in epithelial ovarian carcinoma (EOC) are not widely reported. The purpose of this study is to detect the expression of UBE2C and KAI1 in EOC and their clinical significance.The expression of UBE2C and KAI1 in 180 cases of EOC tissues, 60 cases of normal ovarian epithelial tissues, and 60 cases of ovarian benign tumor tissues were detected by immunohistochemistry. Patients data were also collected.Positive expression of UBE2C in EOC (38.9%) was significantly higher than that both in the normal group (0%) and benign tumors group (10.0%). Furthermore, the expression of UBE2C was positively associated with grades of differentiation, implants, lymph node metastasis (LNM), as well as the International Federation of Gynecology and Obstetrics (FIGO) stages. Positive expression of KAI1 in EOC (25.0%) was significantly lower than that both in the normal group (100%) and benign tumors group (75.0%). And the expression of KAI1 was inversely associated with grades of differentiation, implants, LNM, and FIGO stages. Kaplan-Meier survival analyses demonstrated that UBE2C positive expression for patients with EOC had unfavorably overall survival (OS) time when compared with negative UBE2C for patients. And KAI1 positive expression for patients had favorably OS time when compared with negative KAI1 for patients. Multivariate analysis showed that positive expression of UBE2C and KAI1, implants, and FIGO stages were considered as independently prognostic factors for OS in patients with EOC. Moreover, UBE2C expression was significantly higher in high grade serous adenocarcinoma (SA) when compared with low grade SA; and KAI1 expression was significantly lower in high grade SA when compared with low grade SA. High grade SA patients had higher rates of implants, LNM, and high FIGO stages when compared with low grade SA. High grade SA patients had unfavorably OS time when compared with low grade SA.UBE2C and KAI1 should be considered as potential biomarkers of EOC prognosis.

KAI1 reverses the epithelial-mesenchymal transition in human pancreatic cancer cells

BACKGROUND

Epithelial-mesenchymal transition (EMT) plays an important role in pancreatic cancer (PC). In the present study, we investigated the effects of KAI1 gene overexpression on the EMT of human PC cell lines, MIA PaCa-2 and PACN-1.

METHODS

Plasmids overexpressing KAI1 and pCMV were transfected into MIA PaCa-2 and PACN-1 cells, respectively. After selection of differently transfected cells by G418, KAI1 protein levels were examined by Western blotting, and transfected cells were renamed as MIA PaCa-2-K, MIA PaCa-2-p, PACN-1-K and PACN-1-p. Wound healing and Transwell migration assays were then performed comparing the two groups of cells. EMT-related markers were analyzed by Western blotting.

RESULTS

The percentage of wound closure significantly decreased in MIA PaCa-2-K cells compared with MIA PaCa-2-p and MIA PaCa-2 cells after 24, 48 and 72 h (P < 0.05). In PACN-1-K cells, the percentage of wound closure significantly decreased as well (P < 0.05). Numbers of invading MIA PaCa-2, MIA PaCa-2-p and MIA PaCa-2-K cells were determined as 48.0 ± 15.4, 50.0 ± 12.4, and 12.0 ± 3.8, respectively. The corresponding numbers of invading PACN-1, PACN-1-p and PACN-1-K cells were 29.0 ± 10.6, 31.0 ± 11.4, and 8.0 ± 4.2, respectively. KAI1 overexpression induced a significant upregulation of E-cadherin and also significant downregulation of Snail, vimentin, matrix metalloproteinase 2 (MMP2) and MMP9 (all P < 0.05) in PC cells.

CONCLUSIONS

KAI1 reversed EMT-related marker expression and inhibited migration and invasion of PC cells. Thus, KAI1 might represent a novel potential therapeutic target for PC.

Tetraspanin CD82 represses Sp1-mediated Snail expression and the resultant E-cadherin expression interrupts nuclear signaling of β-catenin by increasing its membrane localization

Tetraspanin membrane proteins form physical complexes with signaling molecules and have been suggested to influence the signaling events of associated molecules. Of the tetraspanin proteins, CD82 has been shown to promote homotypic cell-cell adhesion, which partially accounts for its role in suppressing cancer invasion and metastasis. We found here that CD82-induced cell-cell adhesion is attributed to increased E-cadherin expression through CD82-mediated downregulation of the E-cadherin repressor Snail. The Snail repression by CD82 resulted from the reduced binding of the Sp1 transcription factor to the Snail gene promoter. Notably, high CD82 expression did not allow the fibronectin matrix to induce Sp1 phosphorylation, implicating CD82 inhibition of the fibronectin-integrin signaling-dependent Sp1 activation. Meanwhile, E-cadherin upregulated by CD82 pulled β-catenin up to the membrane region, and consequently reduced the amount of cytoplasmic β-catenin that was able to move into to the nucleus. The Wnt signal-induced nuclear translocation of β-catenin was also inhibited by the CD82 function of upregulating E-cadherin. Overall, high CD82 expression was likely to suppress fibronectin adhesion-induced Sp1 activation signaling for Snail expression, resulting in continuous E-cadherin expression, which contributed not only to the maintenance of strong cell-cell adhesion but also to the blockage of nuclear β-catenin signaling.

Global deletion of tetraspanin CD82 attenuates bone growth and enhances bone marrow adipogenesis

CD82 is a widely expressed member of the tetraspanin family of transmembrane proteins known to control cell signaling, adhesion, and migration. Tetraspanin CD82 is induced over 9-fold during osteoclast differentiation in vitro; however, its role in bone homeostasis is unknown. A globally deleted CD82 mouse model was used to assess the bone phenotype. Based on microCT and 4-point bending tests, CD82-deficient bones are smaller in diameter and weaker, but display no changes in bone density. Histomorphometry shows a decrease in size, erosion perimeter, and number of osteoclasts in situ, with a corresponding increase in trabecular surface area, specifically in male mice. Male-specific alterations are observed in trabecular structure by microCT and in vitro differentiated osteoclasts are morphologically abnormal. Histomorphometry did not reveal a significant reduction in osteoblast number; however, dynamic labeling reveals a significant decrease in bone growth. Consistent with defects in OB function, OB differentiation and mineralization are defective in vitro, whereas adipogenesis is enhanced. There is a corresponding increase in bone marrow adipocytes in situ. Thus, combined defects in both osteoclasts and osteoblasts can account for the observed bone phenotypes, and suggests a role for CD82 in both bone mesenchyme and myeloid cells.

Influence of transcriptional variants on metastasis

Cancer metastasis is defined as the dissemination of malignant cells from the primary tumor site, leading to colonization of distant organs and the establishment of a secondary tumor. Metastasis is frequently associated with chemoresistance and is the major cause of cancer-related mortality. Metastatic cells need to acquire the ability to resist to stresses provided by different environments, such as reactive oxygen species, shear stress, hemodynamic forces, stromal composition, and immune responses, to colonize other tissues. Hence, only a small population of cells has a metastasis-initiating potential. Several studies have revealed the misregulation of transcriptional variants during cancer progression, and many splice events can be used to distinguish between normal and tumoral tissue. These variants, which are abnormally expressed in malignant cells, contribute to an adaptive response of tumor cells and the success of the metastatic cascade, promoting an anomalous cell cycle, cellular adhesion, resistance to death, cell survival, migration and invasion. Understanding the different aspects of splicing regulation and the influence of transcriptional variants that control metastatic cells is critical for the development of therapeutic strategies. In this review, we describe how transcriptional variants contribute to metastatic competence and discuss how targeting specific isoforms may be a promising therapeutic strategy.

The Many and Varied Roles of Tetraspanins in Immune Cell Recruitment and Migration

Immune cell recruitment and migration is central to the normal functioning of the immune system in health and disease. Numerous adhesion molecules on immune cells and the parenchymal cells they interact with are well recognized for their roles in facilitating the movements of immune cells throughout the body. A growing body of evidence now indicates that tetraspanins, proteins known for their capacity to organize partner molecules within the cell membrane, also have significant impacts on the ability of immune cells to migrate around the body. In this review, we examine the tetraspanins expressed by immune cells and endothelial cells that influence leukocyte recruitment and motility and describe their impacts on the function of adhesion molecules and other partner molecules that modulate the movements of leukocytes. In particular, we examine the functional roles of CD9, CD37, CD63, CD81, CD82, and CD151. This reveals the diversity of the functions of the tetraspanin family in this setting, both in the nature of adhesive and migratory interactions that they regulate, and the positive or inhibitory effects mediated by the individual tetraspanin proteins.

The metastasis suppressor CD82/KAI1 inhibits fibronectin adhesion-induced epithelial-to-mesenchymal transition in prostate cancer cells by repressing the associated integrin signaling

The transmembrane protein CD82/KAI1 suppresses the metastatic potential of various cancer cell types. Moreover, decrease or loss of CD82 expression is closely associated with malignancy and poor prognosis in many human cancers including prostate cancer. Despite intense scrutiny, the mechanisms underlying the metastasis-suppressing role of CD82 are still not fully understood. Here, we found that a fibronectin matrix induced mesenchymal phenotypes in human prostate cancer cells with no or low CD82 expression levels. However, high CD82 expression rendered prostate cancer cells to have intensified epithelial characteristics upon fibronectin engagement, along with decreased cell motility and invasiveness. The CD82 function of inhibiting fibronectin-induced epithelial-to-mesenchymal transition (EMT) was dependent not only on CD82 interactions with fibronectin-binding α₃β₁/α₅β₁ integrins but also on the integrin-mediated intracellular signaling events. Notably, CD82 attenuated the FAK-Src and ILK pathways downstream of the fibronectin-receptor integrins. Immunofluorescence staining of human prostate cancer tissue specimens illustrated a negative association of CD82 with EMT-related gene expression as well as prostate malignancy. Altogether, these results suggest that CD82 suppresses EMT in prostate cancer cells adhered to the fibronectin matrix by repressing adhesion signaling through lateral interactions with the associated α₃β₁ and α₅β₁ integrins, leading to reduced cell migration and invasive capacities.

Tspan5 is an independent favourable prognostic factor and suppresses tumour growth in gastric cancer

Tetraspanins are believed to interact with specific partner proteins forming tetraspanin-enriched microdomains and regulate some aspects of partner protein functions. However, the role of Tspan5 during pathological processes, particularly in cancer biology, remains unknown. Here we report that Tspan5 is significantly downregulated in gastric cancer (GC) and closely associated with clinicopathological features including tumour size and TNM stage. The expression of Tspan5 is inversely correlated with patient overall survival and is an independent prognostic factor in GC. Upregulation of Tspan5 in tumour cells results in inhibition of cell proliferation and colony formation in vitro and suppression of xenograft growth of GC by reducing tumour cell proliferation in vivo. Thus, Tspan5 functions as a tumour suppressor in stomach to control the tumour growth. Mechanistically, Tspan5 inhibits the cell cycle transition from G1-S phase by increasing the expression of p27 and p15 and decreasing the expression of cyclin D1, CDK4, pRB and E2F1. The correlation of Tspan5 expression with the expression of p27, p15, cyclin D1, CDK4, pRB and E2F1 in vivo are also revealed in xenografted tumours. Reconstitution of either cyclin D1 or CDK4 in Tspan5-overexpressing GC cells rescues the inhibitory phenotype produced by Tspan5, suggesting that cyclin D1/CDK4 play a dominant role in mediating the suppression of tumour growth by Tspan5 in GC. Our results suggest that Tspan5 may serve as a prognostic biomarker for predicting outcome of GC patients and provide new insights into the pathogenesis of GC and rational for the development of clinical intervention strategies against GC.

Differential tumor biological role of the tumor suppressor KAI1 and its splice variant in human breast cancer cells

The tetraspanin and tumor suppressor KAI1 is downregulated or lost in many cancers which correlates with poor prognosis. KAI1 acts via physical/functional crosstalk with other membrane receptors. Also, a splice variant of KAI1 (KAI1-SP) has been identified indicative of poor prognosis. We here characterized differential effects of the two KAI1 variants on tumor biological events involving integrin (αvß3) and/or epidermal growth factor receptor (EGF-R). In MDA-MB-231 and -435 breast cancer cells, differential effects were documented on the expression levels of the tumor biologically relevant integrin αvß3 which colocalized with KAI1-WT but not with KAI1-SP. Cellular motility was assessed by video image processing, including motion detection and vector analysis for the quantification and visualization of cell motion parameters. In MDA-MB-231 cells, KAI1-SP provoked a quicker wound gap closure and higher closure rates than KAI1-WT, also reflected by different velocities and average motion amplitudes of singular cells. KAI1-SP induced highest cell motion adjacent to the wound gap borders, whereas in MDA-MB-435 cells a comparable induction of both KAI1 variants was noticed. Moreover, while KAI1-WT reduced cell growth, KAI1-SP significantly increased it going along with a pronounced EGF-R upregulation. KAI1-SP-induced cell migration and proliferation was accompanied by the activation of the focal adhesion and Src kinase. Our findings suggest that splicing of KAI1 does not only abrogate its tumor suppressive functions, but even more, promotes tumor biological effects in favor of cancer progression and metastasis.

Prognostic role of CD82/KAI1 in multiple human malignant neoplasms: a meta-analysis of 31 studies

Tetraspanin CD82, also known as KAI1, was revealed as an attractive prognostic tumor biomarker in recent studies. However, some results of these studies remained debatable and inconclusive. Therefore, we conducted a meta-analysis to clarify the precise predictive value of CD82 in various neoplasms. Qualified studies were identified up to April 27, 2017, by searching PubMed, EMBASE, and the Web of Science. In total, 29 eligible studies were ultimately enrolled in this meta-analysis. Pooled hazard ratios (HRs) with 95% CIs of overall survival and disease/recurrence/progression-free survival were calculated to evaluate the correct prognostic role of CD82. Statistical analysis demonstrated that high expression of CD82 was significantly associated with enhanced overall survival (HR =0.56, 95% CI: 0.47–0.67) and disease/recurrence/progression-free survival (HR =0.42, 95% CI: 0.30–0.59) in cancer patients. Furthermore, we also conducted the subgroup analysis and the results revealed that CD82 was associated with favorable outcomes in cancer patients. Taken together, CD82 could be a promising biomarker for predicting the prognosis of patients with malignant neoplasms, and the biological functions of CD82 are of great research value of the subject.

Aberrant expression of CD133 and CD82 in patients with pediatric acute lymphoblastic leukemia and the clinical significance

Cluster of differentiation (CD)133 is considered to be a marker of leukemia stem cells (LSCs), which are one of the primary causes of occurrence, drug resistance and relapse of acute lymphoblastic leukemia (ALL). CD82, an adhesion molecule, performs an important role in the interaction between LSCs and their niche. The purpose of the present study was to assess CD133 and CD82 expression in patients with pediatric ALL, and to evaluate the association with the clinical data. Using flow cytometric assessment and reverse transcription-polymerase chain reaction, CD133 and CD82 expression levels were measured in the bone marrow (BM) of 37 patients with newly diagnosed (ND) pediatric ALL [ALL-ND; 30 B-cell-ALL (B-ALL) and 7 T-cell-ALL (T-ALL)], in 22 patients with complete remission pediatric ALL (ALL-CR) and in 16 age-matched children without BM disease. BM plasma CD82 concentrations were measured by ELISA. The CD82 mRNA expression level in the patients with ALL-ND was significantly higher compared with that in the controls. CD82 mRNA expression levels in pediatric patients with B cell-ALL (B-ALL) were higher than those in ALL-CR patients and controls. For T-ALL, CD82 expression in ND patients was higher than in controls. CD133 mRNA expression levels in patients with pediatric B-ALL-ND were higher than that of controls and patients with ALL-CR. The frequency of CD34⁺ cells in pediatric ALL was significantly higher than that in controls. Frequencies of CD34⁺CD133⁺ or CD34⁺CD82⁺ cells in pediatric ALL were higher than those in controls. A positive association was observed between CD133 and CD82 mRNA expression in patients with B-ALL. A significant association was observed between CD133 mRNA expression and the hyperdiploid karyotype. Therefore, it was considered that CD133 and CD82 may serve an important role in the evolution of pediatric ALL. CD133 and CD82 should be considered as potential markers for the prognosis of patients with ALL.

The metastasis suppressor CD82/KAI1 regulates cell migration and invasion via inhibiting TGF-β 1/Smad signaling in renal cell carcinoma

The tetraspanin KAI1/CD82 was identified as a tumor metastasis suppressor that downregulated in various malignant cell types. However, the function of CD82 and its underlying anti-metastasis role in renal cell carcinoma (RCC) is still unraveled. Here, we investigated the expression of CD82 in RCC and explored its regulatory mechanism in RCC cell lines. We found that CD82 was down-regulated in RCC tissues and cells and its expression was significantly associated with histological grade(p=0.041), tumour stage (p=0.036) and tumor size(p=0.020) by analyzing tissue microarrays. After upregulation of CD82 through lentivirus, reduced ability of migration and invasion in Caki-1 cells were detected. In contrast, gene silencing of CD82 by small interfering RNA promoted metastatic and invasive potential of 786-O cells. Furthermore, Western blot was performed to identify the influence of CD82 on MMP family and TGF-β1/Smad pathway in RCC. Subsequently, upregulating protein level of TGF-β1 with the overexpression of CD82 could rescue the malignant behaviors inhibited by CD82 which indicated that CD82 played its inhibitory role in RCC partially by attenuating the expression of TGF-β1. Taken together, CD82 played a prominent role in migration and invasion of RCC cells and it might exhibit its inhibitory role in RCC metastasis via block TGF-β1/Smad signaling pathway.

Evaluation of the correlation of vasculogenic mimicry, ALDH1, KAI1 and microvessel density in the prediction of metastasis and prognosis in colorectal carcinoma

Background

Metastasis and recurrence are the most common reasons for treatment failure of colorectal carcinoma (CRC). Vasculogenic mimicry (VM, blood supply formation often seen in highly aggressive tumors), Aldehyde dehydrogenase 1 (ALDH1, a biomarker of cancer stem cells), KAI1 (a suppressor gene of tumor metastasis) are all valuable factors for metastasis and prognosis in diverse human cancers. However, the correlation of VM, ALDH1, KAI1 and microvessel density (MVD) in CRC is unclear. In this study, we analyzed the correlations among VM, ALDH1, KAI1 and MVD, as well as their respective correlations with clinicopathological parameters and survival in CRC.

Methods

The level of VM, ALDH1, KAI1 and MVD in 204 whole tissue samples of CRC were examined by immunhistochemistry. Clinical data was also collected.

Results

Levels of VM, ALDH1 and MVD were significantly higher, and levels of KAI1 significantly lower, in CRC tissues than in normal colorectal tissues. Levels of VM, ALDH1 and MVD were positively associated with invasion of depth, lymph node metastasis (LNM), distant metastasis and tumor-node-metastasis (TNM) stages, and negatively with patients’ overall survival (OS). Levels of KAI1 was negatively correlated with invasion of depth, LNM, distant metastasis and TNM stages, and the KAI1 positive expression subgroup had significantly longer OS than did the KAI1- subgroup. In multivariate analysis, high levels of VM, ALDH1 and KAI1, as well as TNM stages were independently correlated with lower OS in patients with CRC.

Conclusions

VM, MVD and the expression of ALDH1 and KAI1 may represent promising metastatic and prognostic biomarkers, as well as potential therapeutic targets for CRC.

Overexpression of KAI1 inhibits retinoblastoma metastasis in vitro

The present study aimed to investigate the expression of cluster of differentiation 82 (KAI1), a gene involved in the suppression of tumor metastasis, in human retinoblastoma (RB) tissue and to study the effect of KAI1 expression on RB cell migration and invasion. KAI1 expression was examined in 26 patients with non-invasive and invasive retinoblastoma using reverse transcription-quantitative polymerase chain reaction and western blot analysis. A lentiviral vector containing KAI1 cDNA was used to transfect the two RB cell lines, HXO-Rb44-Gl and Y79. Following successful transfection, the migratory and invasive capacity of the two RB cell lines was evaluated using a Transwell^® migration assay. KAI1 expression was observed to be downregulated in invasive RB compared to non-invasive RB. The migratory and invasive capacities of KAI1 transfected cell lines were significantly decreased compared to those of the control cells. KAI1 may be involved in retinoblastoma metastasis, and increased expression of KAI1 significantly inhibits the metastatic ability of RB cells in vitro.

The expression of metastasis-associated in colon cancer-1 and KAI1 in gastric adenocarcinoma and their clinical significance

Background

The most common reason for malignant tumor treatment failure is recurrence and metastasis. Metastasis-associated in colon cancer-1 (MACC1) was originally identified as a metastatic and prognostic biomarker for colon cancer and later other solid tumors. Kangai 1 (KAI1), a marker of suppressor of metastasis, is also associated with metastasis and poor prognosis in many tumors. However, the prognostic value of either MACC1 or KAI1 in gastric adenocarcinoma (GAC) is unclear. In this study, we explored the relationship between MACC1 and KAI1 expression, as well as their respective correlation with clinicopathological features, to determine if either could be helpful for improvement of survival prognosis in GAC patients.

Methods

The expression levels of both MACC1 and KAI1 in 325 whole-tissue sections of GAC were examined by immunohistochemistry. Clinical data was also collected.

Results

MACC1 was significantly overexpressed in GAC tissues when compared to levels in normal gastric tissues; KAI1 was significantly down-expressed in GAC tissues when compared to levels in normal gastric tissues. Investigation of association between MACC1 and KAI1 protein levels with clinicopathological parameters of GAC indicated association between the expression of each with tumor grade, lymph node metastasis, invasive depth, and TNM stages. The overall survival time of patients with MACC1- or KAI1-positive GAC tumors was significantly shorter or longer than that of those who were negative. Importantly, multivariate analysis suggested that positive expression of either MACC1 or KAI1, as well as TNM stage, could be independent prognostic factors for overall survival in patients with GAC.

Conclusions

MACC1 and KAI1 may represent promising metastatic and prognostic biomarkers, as well as potential therapeutic targets, for GAC.

Tetraspanin CD82: a suppressor of solid tumors and a modulator of membrane heterogeneity

Tetraspanin CD82 suppresses the progression and metastasis of a wide range of solid malignant tumors. However, its roles in tumorigenesis and hematopoietic malignancy remain unclear. Ubiquitously expressed CD82 restrains cell migration and cell invasion by modulating both cell-matrix and cell-cell adhesiveness and confining outside-in pro-motility signaling. This restraint at least contributes to, if not determines, the metastasis-suppressive activity and, also likely, the physiological functions of CD82. As a modulator of cell membrane heterogeneity, CD82 alters microdomains, trafficking, and topography of the membrane by changing the membrane molecular landscape. The functional activities of membrane molecules and the cytoskeletal interaction of the cell membrane are subsequently altered, followed by changes in cellular functions. Given its pathological and physiological importance, CD82 is a promising candidate for clinically predicting and blocking tumor progression and metastasis and also an emerging model protein for mechanistically understanding cell membrane organization and heterogeneity.

Src/STAT3 signaling pathways are involved in KAI1-induced downregulation of VEGF-C expression in pancreatic cancer

A previous study by our group demonstrated that overexpression of KAI1 was associated with lymphatic metastasis in pancreatic cancer. The present study further investigated the signaling pathways involved in KAI1‑induced downregulation of vascular endothelial growth factor C (VEGF‑C) and lymphatic metastasis in pancreatic cancer. Immunohistochemistry was performed to examine KAI1 and VEGF‑C expression in 28 surgically resected pancreatic cancer tissues. MIA PaCa‑2 and PCAN1 pancreatic cancer cell lines were transfected with KAI1 overexpression vector. VEGF‑C expression as well as phosphorylation of Src and signal transducer and activator of transcription (STAT)3 were assessed by western blot analysis. Furthermore, the signal transduction inhibitors PP2 and AG490 were used to block the Src and STAT3 signaling pathways, respectively. KAI1 was negatively correlated with VEGF‑C expression in pancreatic tumor samples. In MIA PaCa‑2 cells, VEGF‑C expression was more significantly inhibited by restoration of KAI1 than that in PCAN1 cells. In addition, Src and STAT3 phosphorylation was decreased by KAI1 in MIA PaCa‑2 cells. Of note, pre‑treatment with PP2 efficiently reversed the KAI1-induced enhancement of Src and STAT3 phosphorylation as well as VEGF‑C expression. Pre‑treatment with AG490 efficiently reversed the KAI1-induced enhancement of STAT3 phosphorylation and VEGF‑C expression, but had no effect on the upregulation of Src phosphorylation. The present study identified the involvement of Src/STAT3 signaling pathways in KAI1‑induced downregulation of VEGF‑C expression and suggested the implication of these pathways in lymphatic metastasis of pancreatic cancer.

CD82/KAI1 Maintains the Dormancy of Long-Term Hematopoietic Stem Cells through Interaction with DARC-Expressing Macrophages

Hematopoiesis is regulated by crosstalk between long-term repopulating hematopoietic stem cells (LT-HSCs) and supporting niche cells in the bone marrow (BM). Here, we examine the role of CD82/KAI1 in niche-mediated LT-HSC maintenance. We found that CD82/KAI1 is expressed predominantly on LT-HSCs and rarely on other hematopoietic stem-progenitor cells (HSPCs). In Cd82(-/-) mice, LT-HSCs were selectively lost as they exited from quiescence and differentiated. Mechanistically, CD82-based TGF-β1/Smad3 signaling leads to induction of CDK inhibitors and cell-cycle inhibition. The CD82 binding partner DARC/CD234 is expressed on macrophages and stabilizes CD82 on LT-HSCs, promoting their quiescence. When DARC(+) BM macrophages were ablated, the level of surface CD82 on LT-HSCs decreased, leading to cell-cycle entry, proliferation, and differentiation. A similar interaction appears to be relevant for human HSPCs. Thus, CD82 is a functional surface marker of LT-HSCs that maintains quiescence through interaction with DARC-expressing macrophages in the BM stem cell niche.

Molecular cloning, expression pattern, and phylogenetic analysis of a tetraspanin CD82-like molecule in lamprey Lampetra japonica

CD82, a member of the tetraspanins, is originally identified as an accessory molecule in T cell activation, and it participates in the formation of immune synapse both in T cells and antigen-presenting cells of jawed vertebrates. In the present study, a CD82 homologous complementary DNA (cDNA) sequence is identified in the lamprey Lampetra japonica. The open reading frame of this sequence is 801 bp long and encodes a 266-amino acid protein. The multialignment of this sequence with several typical CD82s and CD37s of jawed vertebrates shows that it also possesses their conserved four transmembrane domains and a six-cysteine motif Cys-Cys-Gly…Cys-Ser-Cys…Cys…Cys, which is a characteristic motif of CD82 and CD37 vertebrate tetraspanin sequences. Since it is close to CD82s in sequence similarity, we name it as Lja-CD82-like. From the distribution profile of the conserved motifs of CD82-like, CD82, and CD37 molecules from molluscas to mammals, it seems that the CD82s and CD37s evolved from a common ancestral gene through a gene duplication event to their modern forms by a short insertion or substitution approaches. The phylogenetic analysis indicated that CD82 and CD37 molecules of jawed vertebrates originated from a common ancestral gene which is close to agnathan CD82-like and evolved into two distinct paralogous groups maybe after the divergence of jawed and jawless vertebrates. An expression vector with trigger factor (TF) was constructed to ensure that Lja-CD82-like express in prokaryotic expression host. The expressions of Lja-CD82-like messenger RNA (mRNA) and protein in immune-related tissues of lamprey were detected by real-time quantitative polymerase chain reaction and western blotting. Results showed that the mRNA and the protein levels of Lja-CD82-like were significantly upregulated in lymphocyte-like cells, gills, and supraneural myeloid bodies after stimulation with mixed antigens, respectively. Our data provided a foundation for the further study of Lja-CD82-like and its role in immune response process of jawless vertebrates.

Dendritic Cell Migration and Antigen Presentation Are Coordinated by the Opposing Functions of the Tetraspanins CD82 and CD37

This study supports a new concept where the opposing functions of the tetraspanins CD37 and CD82 may coordinate changes in migration and Ag presentation during dendritic cell (DC) activation. We have previously published that CD37 is downregulated upon monocyte-derived DC activation, promotes migration of both skin and bone marrow-derived dendritic cells (BMDCs), and restrains Ag presentation in splenic and BMDCs. In this article, we show that CD82, the closest phylogenetic relative to CD37, appears to have opposing functions. CD82 is upregulated upon activation of BMDCs and monocyte-derived DCs, restrains migration of skin and BMDCs, supports MHC class II maturation, and promotes stable interactions between T cells and splenic DCs or BMDCs. The underlying mechanism involves the rearrangement of the cytoskeleton via a differential activation of small GTPases. Both CD37(-/-) and CD82(-/-) BMDCs lack cellular projections, but where CD37(-/-) BMDCs spread poorly on fibronectin, CD82(-/-) BMDCs are large and spread to a greater extent than wild-type BMDCs. At the molecular level, CD82 is a negative regulator of RhoA, whereas CD37 promotes activation of Rac-1; both tetraspanins negatively regulate Cdc42. Thus, this study identifies a key aspect of DC biology: an unactivated BMDC is CD37(hi)CD82(lo), resulting in a highly motile cell with a limited ability to activate naive T cells. By contrast, a late activated BMDC is CD37(lo)CD82(hi), and thus has modified its migratory, cytoskeletal, and Ag presentation machinery to become a cell superbly adapted to activating naive T cells.

Tetraspanin CD82 regulates bone marrow homing of acute myeloid leukemia by modulating the molecular organization of N-cadherin

Communication between acute myeloid leukemia (AML) and the bone marrow microenvironment is known to control disease progression. Therefore, regulation of AML cell trafficking and adhesion to the bone marrow is of significant interest. In this study, we demonstrate that differential expression of the membrane scaffold CD82 modulates the bone marrow homing of AML cells. By combining mutational analysis and super-resolution imaging, we identify membrane protein clustering by CD82 as a regulator of AML cell adhesion and bone marrow homing. Cluster analysis of super-resolution data indicates that N-linked glycosylation and palmitoylation of CD82 are both critical modifications that control the microdomain organization of CD82 as well as the nanoscale clustering of associated adhesion protein, N-cadherin. We demonstrate that inhibition of CD82 glycosylation increases the molecular packing of N-cadherin and promotes the bone marrow homing of AML cells. In contrast, we find that inhibition of CD82 palmitoylation disrupts the formation and organization of N-cadherin clusters and significantly diminishes bone marrow trafficking of AML. Taken together, these data establish a mechanism where the membrane organization of CD82, through specific post-translational modifications, regulates N-cadherin clustering and membrane density, which impacts the in vivo trafficking of AML cells. As such, these observations provide an alternative model for targeting AML where modulation of protein organization within the membrane may be an effective treatment therapy to disrupt the bone marrow homing potential of AML cells.

Homozygous loss of mouse tetraspanin CD82 enhances integrin αIIbβ3 expression and clot retraction in platelets

Integrin αIIbβ3 is critical for platelet-mediated blood clotting. Tetraspanins are well-established regulators of integrins and genetic loss of tetraspanin CD151 or TSSC6 in mice leads to increased bleeding due to inadequate integrin αIIbβ3 outside-in signaling. Conversely, mild but enhanced integrin αIIbβ3 activation and hyperaggregation is observed in CD9 and CD63 null mice respectively. CD82 is reportedly expressed in platelets; however its function is unknown. Using genetically engineered CD82 null mice, we investigated the role of the tetraspanin CD82 in platelet activation. Loss of CD82 resulted in reduced bleed times in vivo. CD82 was present on the surface of both human and mouse platelets, and its levels did not change upon platelet activation or degranulation. No differences in platelet activation, degranulation, or aggregation in response to ADP or collagen were detected in CD82 null mice. However, the kinetics of clot retraction was enhanced, which was intrinsic to the CD82-null platelets. Integrin αIIbβ3 surface expression was elevated on the platelets from CD82 null mice and they displayed enhanced adhesion and tyrosine kinase signaling on fibrinogen. This is the first report on CD82 function in platelets; which we found intrinsically modulates clot retraction, integrin αIIbβ3 expression, cell adhesion, and tyrosine signaling.

Impact of KITENIN on tumor angiogenesis and lymphangiogenesis in colorectal cancer

Angiogenesis and lymphangiogenesis are involved in the dissemination of tumor cells from solid tumors to regional lymph nodes and various distant sites. KAI1 COOH-terminal interacting tetraspanin (KITENIN) contributes to tumor progression and poor clinical outcomes in various cancers including colorectal cancer. The aim of the present study was to evaluate whether KITENIN affects tumor angiogenesis and lymphangiogenesis in colorectal cancer. A KITENIN small interfering RNA vector was used to silence KITENIN expression in colorectal cancer cell lines including DLD1 and SW480 cells. To evaluate the ability of KITENIN to induce angiogenesis and lymphangiogenesis in human umbilical vein endothelial cells (HUVECs) and lymphatic endothelial cells (HLECs), we performed Matrigel invasion and tube formation assays. Immunohistochemistry was used to determine the expression of KITENIN in colorectal cancer tissues. Angiogenesis and lymphangiogenesis were evaluated by immunostaining with CD34 and D2-40 antibodies. KITENIN silencing inhibited both HUVEC invasion and tube formation in the DLD1 and SW480 cells. KITENIN silencing led to decreased expression of the angiogenic inducers vascular endothelial growth factor (VEGF)-A and hypoxia-inducible factor-1α and increased expression of the angiogenic inhibitor angiostatin. KITENIN silencing did not inhibit either HLEC invasion or tube formation in all tested cells, but it resulted in decreased expression of the lymphangiogenic inducer VEGF-C. KITENIN expression was significantly associated with tumor stage, depth of invasion, lymph node and distant metastases and poor survival. The mean microvessel density was significantly higher in the KITENIN-positive tumors than that in the KITENIN-negative tumors. However, the mean lymphatic vessel density of KITENIN-positive tumors was not significantly higher than that of the KITENIN-negative tumors. These results suggest that KITENIN promotes tumor progression by enhancing angiogenesis in colorectal cancer.

EGFR over-expression in non-small cell lung cancers harboring EGFR mutations is associated with marked down-regulation of CD82

Epidermal growth factor receptor (EGFR) gene mutations are strongly associated with lung adenocarcinoma and favorable response to EGFR tyrosine kinase inhibitor. The mutated EGFR proteins (EGFRs) are hyper-phosphorylated and refractory to receptor down-regulation. To address the discrepancy between hyper-phosphorylation and lack of down-regulation of mutant EGFRs, we have examined the expression of EGFR negative regulators in non-small cell lung cancer (NSCLC) cell lines. We found that NSCLC cell lines expressing mutant EGFRs often had low expression of various negative regulators for EGFR. Among them, tumor suppressor CD82 was up-regulated by wild type (WT) EGFR but down-regulated by mutant EGFRs. Reconstitution of CD82 exerted stronger suppressive effects on mutant EGFRs than on WT EGFR. Active exportation of CD82 through the exosome was one of the mechanisms involved in achieving the overall CD82 down-regulation in mutant EGFR-expressing lung cancer cell lines. Over-expression of mutant EGFR protein frequently occurred in the lung cancer tissues of mutant EGFR-transgenic mice and also associated with CD82 down-regulation. Immunoblot analyses on the tumor tissues from 23 lung adenocarcinoma patients (12 with WT EGFR, and 11 with mutant EGFRs) also identified significantly stronger down-regulation of CD82 in tumors with mutant EGFRs than WT. Our data indicate that CD82 down-regulation could be a critical step involved in the EGFR over-expression and the stronger tumorigenic activity triggered by EGFR mutations. Up-regulation of the CD82 level may become a promising new treatment strategy for lung adenocarcinoma.

Clinicopathological significance of CD133 and CD44 expression in infiltrating ductal carcinoma and their relationship to angiogenesis

BACKGROUND

Breast cancer is the leading cause of cancer death in females worldwide, and the majority type is infiltrating ductal carcinoma (IDC). Most of IDC patients died of metastasis and recurrence. Cancer stem cells (CSCs) are defined with the ability to be self-renewal and potentially promote proliferation and formation of tumors. CSCs are related to angiogenesis and are important targets in new cancer treatment strategies. In this study, we purposed to investigate on expression and clinical significances of CSCs marked by CD133 and CD44 in IDC and their relationship to angiogenesis.

METHODS

The specimens of IDC from 325 Chinese patients with follow-up were analyzed for CD133, CD44, CD82, and CD34 protein expression by immunohistochemical staining. The Pearson chi-square test and t test were used to assess the associations among the positive staining of these markers and clinicopathological characteristics. Postoperative overall survival time in these patients with IDC was analyzed by univariate and multivariate analyses.

RESULTS

In IDC tissues, positive rates of 48.6%, 53.8%, and 42.2% were obtained for CD133, CD44, and CD82 protein, respectively; the mean score of microvessel density (MVD) was 20.5 ± 7.0 in IDC group. And there was a significant difference between the two groups. There was a positive relationship between the expression of CD133, CD44, and the score of MVD and the grades of tumor, lymph node metastasis, tumor-node-metastasis (TNM) stages (all P < 0.05); and the expression of CD82 was negatively related to grades of tumor, lymph node metastasis, and TNM stages (all P < 0.05). The overall mean survival time of the patients with CD133, CD44, and the score of MVD (≥21) positive expression was lower than that of patients with negative expression. The overall mean survival time of patients of CD82-positive expression was longer than that of patients of the negative expression group. The positive expression of CD133 and CD82, and TNM stages were independent prognostic factors of IDC (P < 0.05).

CONCLUSIONS

CSCs, angiogenesis, and aberrant expression of CD82 may be involved in the initiation, development, metastasis, and recurrence. It is suggested that CSCs, angiogenesis, and CD82 be possible as a therapeutic marker for anti-tumor therapy.

The host microenvironment influences prostate cancer invasion, systemic spread, bone colonization, and osteoblastic metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in men worldwide. Most PCa deaths are due to osteoblastic bone metastases. What triggers PCa metastasis to the bone and what causes osteoblastic lesions remain unanswered. A major contributor to PCa metastasis is the host microenvironment. Here, we address how the primary tumor microenvironment influences PCa metastasis via integrins, extracellular proteases, and transient epithelia-mesenchymal transition (EMT) to promote PCa progression, invasion, and metastasis. We discuss how the bone-microenvironment influences metastasis; where chemotactic cytokines favor bone homing, adhesion molecules promote colonization, and bone-derived signals induce osteoblastic lesions. Animal models that fully recapitulate human PCa progression from primary tumor to bone metastasis are needed to understand the PCa pathophysiology that leads to bone metastasis. Better delineation of the specific processes involved in PCa bone metastasize is needed to prevent or treat metastatic PCa. Therapeutic regimens that focus on the tumor microenvironment could add to the PCa pharmacopeia.

Alternative splicing of KAI1 abrogates its tumor-suppressive effects on integrin αvβ3-mediated ovarian cancer biology

Loss or downregulation of the tumor-suppressor KAI1 correlates with poor cancer patient prognosis. KAI1 functions by interacting with other proteins, including integrin cell adhesion and signaling receptors. We previously showed that KAI1 physically and functionally crosstalks with the tumor-biologically relevant integrin αvβ3, thereby suppressing ovarian cancer cell migration and proliferation. Interestingly, in metastases, a KAI1 splice variant had been identified, indicating poor patient prognosis. Thus, we here characterized differential effects of the two KAI1 proteins upon their cellular restoration. Opposite to KAI1, KAI1-splice reduced αvβ3-mediated cell adhesion, thereby inducing cell migration. This was accompanied by elevated αvβ3 levels and drastically elevated focal adhesion kinase activation, however, without any obvious colocalization with αvβ3, as observed for KAI1. Moreover, codistribution of KAI1 with the cell/cell-adhesion molecule E-cadherin was abrogated in KAI1-splice. Whereas KAI1 diminished cell proliferative activity, KAI1-splice prominently enhanced cell proliferation concomitant with elevated transcription and cell-surface expression of the epidermal growth factor receptor. Thus KAI1-splice does not only counteract the tumor-suppressive actions of KAI1, but - beyond that - promotes αvβ3-mediated biological functions in favor of tumor progression and metastasis.

Aberrant expression of the autocrine motility factor receptor correlates with poor prognosis and promotes metastasis in gastric carcinoma

AMFR, autocrine motility factor receptor, also called gp78, is a cell surface cytokine receptor which has a dual role as an E3 ubiquitin ligase in endoplasmic reticulum-associated degradation. AMFR expression is associated with tumor malignancy. We here investigated the clinical significance of AMFR and its role in metastasis and prognosis in gastric cancer. Expression of AMFR, E-cadherin and N-cadherin in cancer tissues and matched adjacent normal tissues from 122 gastric cancer (GC) patients undergoing surgical resection was assessed by immunohistochemistry. Levels of these molecules in 17 cases selected randomly were also analysed by Western blotting. AMFR expression was significantly increased in gastric cancer tissues, and associated with invasion depth and lymph node metastasis. Kaplan-Meier analysis showed AMFR expression correlated with poor overall survival and an increased risk of recurrence in the GC cases. Cox regression analysis suggested AMFR to be an independent predictor for overall and recurrence-free survival. E-cadherin expression was decreased in gastric cancer tissues; conversely, N-cadherin was increased. Expression of AMFR negatively correlated with E-cadherin expression, whereas N-cadherin expression showed a significant positive correlation with AMFR expression. AMFR might be involved in the regulation of epithelial-mesenchymal transition, with aberrant expression correlating with a poor prognosis and promoting invasion and metastasis in GCs.

Hepatitis B virus inhibits the expression of CD82 through hypermethylation of its promoter in hepatoma cells

The tumor suppressor gene CD82, also known as KAI1, may act as a general suppressor of metastasis in numerous types of cancer. It is hypothesized that downregulation of CD82 gene expression may be an important factor in the induction of hepatocellular carcinoma (HCC), however the mechanism for this requires further study. In the present study, the relative mRNA and protein expression levels of the CD82 gene were determined in HCC and adjacent non‑tumor tissues. The association between the CD82 gene and the hepatitis B virus (HBV) was also investigated, by quantitative polymerase chain reaction, western blotting, luciferase reporter assays and mass spectrometry with matrix‑assisted laser desorption/ionization time‑of‑flight mass array. CD82 expression was shown to be suppressed in response to HCC promoter methylation. Relative CD82 mRNA and protein expression levels were downregulated in HCC tissues (P<0.05). HBx protein inhibited CD82 promoter activity and subsequently the mRNA and protein expression levels. Furthermore, it was demonstrated that HBV could inhibit the expression of CD82 at the transcriptional level, and repress the activity of the CD82 promoter through hypermethylation. In addition, the methyl enzyme inhibitor 5‑aza‑CdR could induce the CD82 promoter activity and the relative expression level of CD82 mRNA, as observed by an increase in luciferase activity driven by the CD82 promoter. The observations of the present study suggest that hypermethylation of the CD82 promoter may be an event leading to the development of HCC. Low expression of CD82 is likely to be involved in tumor progression. HBV may inhibit the expression of CD82 through hypermethylation of the promoter in hepatoma cells.

ΔNp63α activates CD82 metastasis suppressor to inhibit cancer cell invasion

P63 is a p53 family member involved in multiple facets of biology, including embryonic development, cell proliferation, differentiation, survival, apoptosis, senescence and aging. The p63 gene encodes multiple protein isoforms either with (TAp63) or without (ΔNp63) the N-terminal transactivation domain. Amounting evidence suggests that p63 can function as a tumor suppressor, yet the precise molecular mechanisms, and particularly the specific roles of TAp63 and ΔNp63 in cancer progression, are still largely unclear. Here, we demonstrated that ΔNp63α, the predominant isoform expressed in epithelial cells and squamous cell carcinomas, inhibits cell invasion. Affymetrix gene expression profiling, combined with gain- and loss-of-function analyses and chromatin immunoprecipitation, indicated that cluster of differentiation 82 (CD82), a documented metastasis suppressor, is a direct transcriptional target of ΔNp63α. Expression of ΔNp63α inhibited outgrowth in Matrigel and cancer cell invasion, which was largely reversed by specific ablation of CD82. Conversely, ΔNp63α knockdown led to increased cell invasion, which was reversed by ectopic expression of CD82. Moreover, inhibition of glycogen synthase kinase-3β (GSK3β) by either pharmacological inhibitors or by RNA interference resulted in the downregulation of ΔNp63α and CD82 expression, concomitant with increased cell invasion, independently of β-catenin. Furthermore, decreased expression of p63 and CD82 is correlated with cancer progression. Taken together, this study reveals that ΔNp63α upregulates CD82 to inhibit cell invasion, and suggests that GSK3β can regulate cell invasion by modulating the ΔNp63α–CD82 axis.

Clinicopathological significance of cancer stem cells marked by CD133 and KAI1/CD82 expression in laryngeal squamous cell carcinoma

Background

Presently, CD133 is one of the hottest markers to characterize cancer stem cells and KAI1/CD82 is reported as an important marker for the metastasis and prognosis of many cancers. The purpose of our study is to explore the relationship between cancer stem cells (CSCs) marked by CD133 and KAI1/CD82 expression and the clinicopathological characteristics of patients with laryngeal squamous cell carcinoma (LSCC).

Methods

Immunohistochemical analysis was used to detect the expression of CD133 and KAI1/CD82 in 83 archival surgical specimens of human LSCC and 83 cases of normal laryngeal tissues.

Results

In LSCC, positive rates of 49.4% and 41.0% were obtained for CD133 and KAI1/CD82, respectively. The expression of CD133 in LSCC tissues was significantly higher than that in normal tissues (P < 0.001), and the expression of CD133 was positively associated with pTNM stage (P = 0.005), pathological grade (P = 0.001), and lymph node metastasis (P < 0.001). The reduced expression of KAI1/CD82 was present in LSCC tissues. The positive rate of KAI1/CD82 expression was negatively correlated with pTNM stage (P = 0.014), pathological grade (P < 0.001), and lymph node metastasis (P = 0.007). A correlation analysis showed that there was a negative relationship between the expression of CD133 and KAI1/CD82 protein in LSCC tissues (P < 0.001). By Kaplan-Meier analysis, the expression of CD133 was negatively correlated with overall survival (OS) (log-rank = 40.949, P < 0.001) and disease-free survival (DFS) (log-rank = 39.307, P < 0.001) time of LSCC. The expression of KAI1/CD82 was positively correlated with OS (log-rank = 40.279, P < 0.001) and DFS (log-rank = 39.271, P < 0.001) time of LSCC. Cox regression analysis: the expression of CD133 and KAI1/CD82, and pTNM stages were independent prognostic factors of LSCC (P < 0.05).

Conclusions

Thus the detection of CD133 and KAI1/CD82 proteins may be used as a potential indicator of LSCC prognosis.

Tetraspanin TSPAN12 regulates tumor growth and metastasis and inhibits β-catenin degradation

Ablation of tetraspanin protein TSPAN12 from human MDA-MB-231 cells significantly decreased primary tumor xenograft growth, while increasing tumor apoptosis. Furthermore, TSPAN12 removal markedly enhanced tumor-endothelial interactions and increased metastasis to mouse lungs. TSPAN12 removal from human MDA-MB-231 cells also caused diminished association between FZD4 (a key canonical Wnt pathway receptor) and its co-receptor LRP5. The result likely explains substantially enhanced proteosomal degradation of β-catenin, a key effecter of canonical Wnt signaling. Consistent with disrupted canonical Wnt signaling, TSPAN12 ablation altered expression of LRP5, Naked 1 and 2, DVL2, DVL3, Axin 1, and GSKβ3 proteins. TSPAN12 ablation also altered expression of several genes regulated by β-catenin (e.g. CCNA1, CCNE2, WISP1, ID4, SFN, ME1) that may help to explain altered tumor growth and metastasis. In conclusion, these results provide the first evidence for TSPAN12 playing a role in supporting primary tumor growth and suppressing metastasis. TSPAN12 appears to function by stabilizing FZD4-LRP5 association, in support of canonical Wnt-pathway signaling, leading to enhanced β-catenin expression and function.

The membrane scaffold CD82 regulates cell adhesion by altering α4 integrin stability and molecular density

Hematopoietic stem/progenitor cell (HSPC) interactions with the bone marrow microenvironment are important for maintaining HSPC self-renewal and differentiation. In recent work, we identified the tetraspanin protein, CD82, as a regulator of HPSC adhesion and homing to the bone marrow, although the mechanism by which CD82 mediated adhesion was unclear. In the present study, we determine that CD82 expression alters cell-matrix adhesion, as well as integrin surface expression. By combining the superresolution microscopy imaging technique, direct stochastic optical reconstruction microscopy, with protein clustering algorithms, we identify a critical role for CD82 in regulating the membrane organization of α4 integrin subunits. Our data demonstrate that CD82 overexpression increases the molecular density of α4 within membrane clusters, thereby increasing cellular adhesion. Furthermore, we find that the tight packing of α4 into membrane clusters depend on CD82 palmitoylation and the presence of α4 integrin ligands. In combination, these results provide unique quantifiable evidence of CD82's contribution to the spatial arrangement of integrins within the plasma membrane and suggest that regulation of integrin density by tetraspanins is a critical component of cell adhesion.

KAI1 inhibits lymphangiogenesis and lymphatic metastasis of pancreatic cancer in vivo

BACKGROUND

Several studies have shown that KAI1 inhibits tumor metastasis, but its mechanism is not clear. The present study aimed to determine the role of KAI1 in lymphatic metastasis, specifically in pancreatic cancer.

METHODS

The KAI1 gene was transfected into the pancreatic cancer cell line MIA PaCa-2 and PANC-1 by using liposomes and selected by G418, and the protein was measured by Western blotting. After successful infection, the cell growth curve was studied by MTT, vascular endothelial growth factor C (VEGF-C) secretion by pancreatic cancer cell were measured by ELISA. The KAI1 and pCMV transfected MIA PaCa-2 cells were renamed as MIA PaCa-2-K and MIA PaCa-2-p. These two kinds of cells were injected into the subcuticular layer of nude mice; both tumor growth and metastasis through the lymphatic nodes were assessed. Lymphangiogenesis in tumors was measured by immunohistochemistry.

RESULTS

The VEGF-C secretion was significantly reduced in MIA PaCa-2 cells compared with PANC-1 cells after being transfected with the KAI1 gene. The growth rate of subcutaneous tumors was similar after the injection of MIA PaCa-2-K, MIA PaCa-2, and MIA PaCa-2-p. MIA PaCa-2-K tumors showed slower lymphangiogenesis and lymph node metastasis compared with MIA PaCa-2 and MIA PaCa-2-p tumors.

CONCLUSION

The overexpression of KAI1 inhibits the lymphangiogenesis and lymph node metastasis of MIA PaCa-2 pancreatic tumors.

Tetraspanin proteins promote multiple cancer stages

An abundance of evidence shows supporting roles for tetraspanin proteins in human cancer. Many studies show that the expression of tetraspanins correlates with tumour stage, tumour type and patient outcome. In addition, perturbations of tetraspanins in tumour cell lines can considerably affect cell growth, morphology, invasion, tumour engraftment and metastasis. This Review emphasizes new studies that have used de novo mouse cancer models to show that select tetraspanin proteins have key roles in tumour initiation, promotion and metastasis. This Review also emphasizes how tetraspanin proteins can sometimes participate in tumour angiogenesis. These recent data build an increasingly strong case for tetraspanins as therapeutic targets.