A novel strategy for evasion of NK cell immunity by tumours expressing core2 O-glycans.

The O-glycan branching enzyme, core2 ß-1,6-N-acetylglucosaminyltransferase (C2GnT), forms O-glycans containing an N-acetylglucosamine branch connected to N-acetylgalactosamine (core2 O-glycans) on cell-surface glycoproteins. Here, we report that upregulation of C2GnT is closely correlated with progression of bladder tumours and that C2GnT-expressing bladder tumours use a novel strategy to increase their metastatic potential. Our results showed that C2GnT-expressing bladder tumour cells are highly metastatic due to their high ability to evade NK cell immunity and revealed the molecular mechanism of the immune evasion by C2GnT expression. Engagement of an NK-activating receptor, NKG2D, by its tumour-associated ligand, Major histocompatibility complex class I-related chain A (MICA), is critical to tumour rejection by NK cells. In C2GnT-expressing bladder tumour cells, poly-N-acetyllactosamine was present on core2 O-glycans on MICA, and galectin-3 bound the NKG2D-binding site of MICA through this poly-N-acetyllactosamine. Galectin-3 reduced the affinity of MICA for NKG2D, thereby severely impairing NK cell activation and silencing the NK cells. This new mode of NK cell silencing promotes immune evasion of C2GnT-expressing bladder tumour cells, resulting in tumour metastasis.

In vivo selection of high-metastatic subline of bladder cancer cell and its characterization.

The majority of deaths associated with solid tumors are caused by tumor metastasis. To prevent metastasis, it is vital to understand its detailed process. In hematogenous metastasis of bladder cancer, some cancer cells disseminating into blood circulation extravasate into the lung tissues to form metastases. To study the molecular basis of the lung metastasis of bladder cancer, we employed an in vivo selection system that mimics hematogenous metastasis of bladder cancer on a low-metastatic bladder cancer cell line (KK-47). We have successfully isolated a high-metastatic bladder cancer subline, KK-47HM4, from KK-47 cells. We characterized KK-47HM4 in in vitro experimental systems. No significant difference in growth rate and susceptibility to NK cell attack between KK-47 and KK-47HM4 cells was observed. However, KK-47HM4 exhibited the higher capacities of Matrigel Matrix invasion and transendothelial invasion than KK-47. These results suggest that the extravasation of KK-47HM4 cells was enhanced among the multiple steps of the lung metastasis of bladder cancer. Our cDNA microarray analysis identified 67 genes whose expression was up- or downregulated in KK-47HM4 cells compared with KK-47 cells. This analysis data implied that one possible cause for enhanced extravasation of KK-47HM4 is its higher adhesion to extracellular matrix proteins. KK-47HM4 is the first bladder cancer subline with enhanced extravasation potential using the in vivo selection system. The information provided by our cDNA microarray analysis using KK-47HM4 will be useful for further investigation into the molecular basis of extravasation of cancer cells.

Tumor defense systems using O-glycans.

During the process of hematogenous tumor metastasis, tumor cells that dissociated from the primary site enter the blood vessels and are exposed to innate immune systems in host blood circulation. In the innate immune systems, natural killer (NK) cells play a major role in rejecting tumors and suppressing metastasis. To establish metastasis, tumor cells therefore need to defend themselves against tumor rejection by NK cells. It has been recently discovered that some tumor cells develop defense systems against NK cell attack using certain types of cell-surface carbohydrates. The types of carbohydrates attached to cell-surface glycoproteins through serine or threonine residues contain a branch consisting of ß-1,6-linkage of N-acetylglucosamine and N-acetylgalactosamine and are designated as core2 O-glycans. Tumor cells expressing core2 O-glycans evade NK cell-mediated tumor rejection, thereby surviving longer in host circulation and acquiring high-metastatic phenotypes. This review explains two types of tumor defense systems against NK cell immunity using core2 O-glycans.

Requirement for FBP17 in invadopodia formation by invasive bladder tumor cells.

PURPOSE: Invadopodia (protrusions of the plasma membrane formed by invasive tumor cells) have an essential role in bladder tumor invasion. To understand the process of bladder tumor invasion it is crucial to investigate the molecular mechanisms of invadopodia formation. We found that invasive bladder tumor cells express FBP17. In this study we examined the role of FBP17 in bladder tumor cell invadopodia formation and invasion. MATERIALS AND METHODS: We used the 3 bladder tumor cell lines YTS-1, T24 and RT4 (ATCC®), and primary culture of bladder tumors from patients. Cells were stained with phalloidin for invadopodia formation. FBP17 knockdown cells were tested for invadopodia formation and subjected to invasion assay using a Transwell® cell culture chamber. We also examined the role of the extended FER-CIP4 homology and Src homology 3 domains of FBP17 in invadopodia formation in FBP17 mutant constructs. RESULTS: Invadopodia formation was observed in invasive bladder tumor cells and FBP17 was localized to invadopodia in invasive cells. FBP17 knockdown decreased invadopodia formation in invasive cells to 13% to 14% (p <0.0005) and decreased their invasive capacity to 14% to 16% (p <0.001). The extended FER-CIP4 homology and Src homology 3 domains of FBP17 were necessary for invadopodia formation and invasion. CONCLUSIONS: Invadopodia formation requires membrane deformation activity and recruitment of dynamin-2 mediated by FBP17. FBP17 has a critical role in the process of bladder tumor cell invasion by mediating invadopodia formation.

Invadopodia formation by bladder tumor cells.

A major cause of death in patients with bladder tumors is recurrence with metastasis. Bladder tumor metastasis is largely dependent upon the invasive capacity of tumor cells. Tumor cell invasion is mainly mediated by actin-rich protrusive membrane structures called invadopodia. The formation of invadopodia was observed in various types of invasive tumors such as breast cancer and melanomas. However, invadopodia formation so far has not been described in bladder tumor cells. We here report that human bladder tumor cells form functionally active invadopodia. By using a confocal laser scanning microscope, we demonstrated that invasive bladder tumor cell lines, YTS-1 and T24, with high Matrigel degradation activity form invadopodia but that noninvasive bladder tumor cell lines, RT4 and KK-47, form no detectable invadopodia. Invadopodia formed by YTS-1 cells had the ability to secrete matrix metalloproteases and degrade extracellular matrix to invade surrounding areas. Moreover, we observed that primary tumor cells obtained from patients with invasive bladder tumors also form invadopodia, validating the results from bladder tumor cell lines. Our results provide evidence that invasive human bladder tumor cells form invadopodia for tumor invasion.

The role of LIM and SH3 protein-1 in bladder cancer metastasis.

The LIM and SH3 protein-1 (LASP-1) is a multi-domain protein that is involved in several malignant cancers. The role of LASP-1 in malignant phenotypes including high invasive properties and unrestricted cell proliferation, remain to be elucidated. The present study reported the association of LASP-1 expression with bladder cancer malignancy and its role in cancer cell invasion and proliferation. The immunohistochemical analysis of the expression status of LASP-1 in radical cystectomy specimens from invasive bladder cancer patients revealed that the LASP-1-positive patients demonstrated a decreased survival rate compared with the LASP-1-negative patients. The expression level of LASP-1 was increased in invasive bladder cancer cell lines compared with the non-invasive bladder cancer cell lines. Invasive cancer cells form invadopodia, the filamentous actin-based membrane protrusions that are essential in cancer cell invasion. Knockdown of LASP-1 reduced the ability to form invadopodia, resulting in decreased invasive capacity of the LASP-1 knockdown cells. In addition, knockdown of LASP-1 reduced cell proliferation. These results suggest that LASP-1 is important in invadopodia formation and cell proliferation of bladder cancer cells, promoting the malignant properties and resulting in poor-prognosis.

A mechanism for evasion of CTL immunity by altered O-glycosylation of HLA class I.

Anti-tumour immunity by cytotoxic T-lymphocytes (CTLs) is essential to suppress tumour progression. Cancer cells that evade CTL immunity proliferate in the host, promoting metastasis, but mechanisms underlying this capacity remain unknown. Here we report that bladder cancer cells metastasized to lymph nodes evade CTL immunity by a new mechanism via altered glycosylation. CTLs normally recognize and kill cancer cells presenting antigenic peptides on human leukocyte antigen (HLA) class I. We show bladder cancer cells expressing the O-glycan processing enzyme, core2 ß-1,6-N-acetylglucosaminyltransferase (C2GnT) exhibit HLA class I O-glycan modified with poly-N-acetyllactosamine and are highly susceptible to CTL. In those cells, poly-N-acetyllactosamine on HLA class I O-glycan binds galectin-3 to form a cell-surface molecular lattice, enabling efficient cell-surface retention of HLA class I. In contrast, bladder cancer cells in which C2GnT is downregulated show decreased levels of poly-N-acetyllactosamine on HLA class I O-glycans, attenuating lattice formation and reducing the cell-surface half-life of HLA class I. These tumour cells present antigenic peptides less efficiently, thereby evading CTL lysis and facilitating metastasis.

Vimentin intermediate filament and plectin provide a scaffold for invadopodia, facilitating cancer cell invasion and extravasation for metastasis.

To investigate the molecular mechanisms of cancer metastasis, we have isolated a high-metastatic bladder cancer cell subpopulation from a low-metastatic cell line by using an in vivo selection system. Cells in the subpopulation showed a high ability to form invadopodia, the filamentous actin (F-actin)-based membrane protrusions that play an essential role in cancer cell invasion. Analysis of the gene expression profile revealed that the expression of an intermediate filament (IF) protein, vimentin and a cytoskeletal linker protein, plectin was up-regulated in the high-metastatic subpopulation compared with the low metastatic cell line. Here we report a novel role of vimentin IF and plectin in metastasis. In invasive bladder cancer cells, the vimentin IF-plectin-invadopodia F-actin link was formed. Disruption of this link severely impaired invadopodia formation, reducing the capacities of extracellular matrix degradation, transendothelial migration and metastasis. In addition, the vimentin assembly into the filaments was required for invadopodia formation. Our results suggest that plectin anchoring invadopodia to vimentin IF scaffolds and stabilizes invadopodia, which is a critical molecular process for cancer cell invasion and extravasation for metastasis.

Invadopodia are essential in transurothelial invasion during the muscle invasion of bladder cancer cells.

Muscle invasive bladder cancer is an aggressive type of epithelial tumor with a high rate of metastasis. For bladder cancer cells to reach the muscle layer, cells must invade through an urothelial cell monolayer (transurothelial invasion) and basement membrane. However, the process by which transurothelial invasion occurs has not been fully characterized. In this study we developed a novel method to evaluate the transurothelial invasion capacity and investigated its cellular and molecular processes using primary culture cells from bladder cancer patients. The analysis revealed that compared with the prognosis for patients with non­muscle invasive bladder cancer that of patients with muscle invasive bladder cancer was particularly poor due to metastatic recurrence. Cancer cells from patients with muscle invasive bladder cancer exhibited a higher invasive capacity through the urothelial cell monolayer compared with those from non­invasive bladder cancer patients. Furthermore, muscle invasive bladder cancer cells demonstrated a greater ability to form invadopodia, the filamentous actin­based membrane protrusions required for matrix degradation and invasion compared with non­invasive cells. Bladder cancer cell lines were established with reduced invadopodia formation by silencing the expression of cortactin, an essential component of invadopodia. The cortactin knockdown bladder cancer cells with reduced invadopodia formation demonstrated a markedly reduced ability to invade through the urothelial cell monolayer, indicating that invadopodia are essential for transurothelial invasion. The results indicate that invadopodia formation is required for muscle invasion of aggressive bladder cancer cells.

Extravasation during bladder cancer metastasis requires cortactin­mediated invadopodia formation.

Invasive cancer cells form the filamentous actin­based membrane protrusions known as invadopodia. Invadopodia are thought to play a critical role in cancer cell invasion and metastasis due to their ability to degrade the extracellular matrix. The present study assessed whether invadopodia formation is essential in extravasation of circulating bladder cancer cells and lung metastasis. To analyze the importance of invadopodia, bladder cancer cell lines with reduced invadopodia formation were established by silencing the expression of cortactin, an essential component of invadopodia, using cortactin short hairpin RNA. Bladder cancer cells with cortactin knockdown demonstrated a markedly decreased ability to form invadopodia, secrete matrix metalloproteinases and invade the extracellular matrix. In addition, the knockdown cells exhibited a reduced transendothelial invasion capacity and decreased formation of metastatic foci in the lungs. The present study demonstrated that bladder cancer cells with cortactin knockdown have a reduced capacity to extravasate into the lung from the circulation, due to the decreased invasive character of invadopodia. This suggests that invadopodia formation is a critical process for cancer cell extravasation.

Core2 O-glycan-expressing prostate cancer cells are resistant to NK cell immunity.

Core2 ß-1,6-N-acetylglucosaminyltransferase (C2GnT) forms an N-acetylglucosamine branch in the O-glycans (core2 O-glycans) of cell surface glycoproteins. We previously revealed that the expression of C2GnT is positively correlated with poor prognosis in prostate cancer patients. However, the detailed mechanisms underlying their poor prognosis remain unclear. In the current study, we report that the core2 O-glycans carried by the surface MUC1 glycoproteins of prostate cancer cells play an important role in the evasion of NK cell immunity. In C2GnT­expressing prostate cancer cells, the MUC1 core2 O-glycans are modified with poly-N-acetyllactosamine. MUC1 glycoproteins carrying poly-N-acetyllactosamine attenuated the interaction of the cancer cells with NK cells, resulting in decreased secretion of granzyme B by the NK cells. Poly­N­acetyllactosamine also interfered with the ability of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to access the cancer cell surface. These effects of poly-N-acetyllactosamine on NK cells render C2GnT-expressing prostate cancer cells resistant to NK cell cytotoxicity. By contrast, C2GnT-deficient prostate cancer cells carrying a lower amount of poly-N-acetyllactosamine than the C2GnT-expressing prostate cancer cells were significantly more susceptible to NK cell cytotoxicity. Our results strongly suggest that C2GnT-expressing prostate cancer cells evade NK cell immunity and survive longer in the host blood circulation, thereby resulting in the promotion of prostate cancer metastasis.

Two opposing roles of O-glycans in tumor metastasis.

Despite the high prevalence of metastatic cancers and the poor outcome for patients, the processes of tumor metastasis still remain poorly understood. It has been shown that cell-surface carbohydrates attached to proteins through the amino acids serine or threonine (O-glycans) are involved in tumor metastasis, with the roles of O-glycans varying depending on their structure. Core2 O-glycans allow tumor cells to evade natural killer (NK) cells of the immune system and survive longer in the circulatory system, thereby promoting tumor metastasis. Core3 O-glycans or O-mannosyl glycans suppress tumor formation and metastasis by modulating integrin-mediated signaling. Here, we highlight recent advances in our understanding of the detailed molecular mechanisms by which O-glycans promote or suppress tumor metastasis.

MUC1 carrying core 2 O-glycans functions as a molecular shield against NK cell attack, promoting bladder tumor metastasis.

Core 2 ß-1,6-N-acetylglucosaminyltransferase (C2GnT) forms an N-acetylglucosamine branch in O-glycans (core 2 O-glycans) of cell surface glycoproteins. C2GnT-expressing bladder tumors acquire highly metastatic phenotypes by surviving longer in host blood circulation. However, the detailed mechanisms underlying this increased survival remain unclear. In this study, we report that the expression of C2GnT in bladder tumors positively correlates with tumor progression and that bladder tumor cell-surface mucin 1 (MUC1) carrying core 2 O-glycans plays an important role in the evasion from natural killer (NK) cell attack. In C2GnT-expressing bladder tumor cells, heavily core 2 O-glycosylated MUC1 carries poly-N-acetyllactosamine in its O-glycans and galectin-3 binds to MUC1 through this poly-N-acetyllactosamine. The binding of galectin-3 to poly-N-acetyllactosamine in MUC1 core 2 O-glycans attenuates the interaction of the tumor cells with NK cells and interferes with the access of tumor necrosis factor-related apoptosis-inducing ligand to the tumor cell surface. These effects of MUC1 carrying core 2 O-glycans on NK cell attack facilitate C2GnT-expressing tumor cells to evade NK cell immunity and survive longer in host blood circulation. We reveal that MUC1 carrying core 2 O-glycans thus functions as a molecular shield against NK cell attack, thereby promoting bladder tumor metastasis.

FBP17 Mediates a Common Molecular Step in the Formation of Podosomes and Phagocytic Cups in Macrophages.

Macrophages act to protect the body against inflammation and infection by engaging in chemotaxis and phagocytosis. In chemotaxis, macrophages use an actin-based membrane structure, the podosome, to migrate to inflamed tissues. In phagocytosis, macrophages form another type of actin-based membrane structure, the phagocytic cup, to ingest foreign materials such as bacteria. The formation of these membrane structures is severely affected in macrophages from patients with Wiskott-Aldrich syndrome (WAS), an X chromosome-linked immunodeficiency disorder. WAS patients lack WAS protein (WASP), suggesting that WASP is required for the formation of podosomes and phagocytic cups. Here we have demonstrated that formin-binding protein 17 (FBP17) recruits WASP, WASP-interacting protein (WIP), and dynamin-2 to the plasma membrane and that this recruitment is necessary for the formation of podosomes and phagocytic cups. The N-terminal EFC (extended FER-CIP4 homology)/F-BAR (FER-CIP4 homology and Bin-amphiphysin-Rvs) domain of FBP17 was previously shown to have membrane binding and deformation activities. Our results suggest that FBP17 facilitates membrane deformation and actin polymerization to occur simultaneously at the same membrane sites, which mediates a common molecular step in the formation of podosomes and phagocytic cups. These results provide a potential mechanism underlying the recurrent infections in WAS patients.

Requirement for a complex of Wiskott-Aldrich syndrome protein (WASP) with WASP interacting protein in podosome formation in macrophages.

Chemotactic migration of macrophages is critical for the recruitment of leukocytes to inflamed tissues. Macrophages use a specialized adhesive structure called a podosome to migrate. Podosome formation requires the Wiskott-Aldrich syndrome protein (WASP), which is a product of the gene defective in an X-linked inherited immunodeficiency disorder, the Wiskott-Aldrich syndrome. Macrophages from WASP-deficient Wiskott-Aldrich syndrome patients lack podosomes, resulting in defective chemotactic migration. However, the molecular basis for podosome formation is not fully understood. I have shown that the WASP interacting protein (WIP), a binding partner of WASP, plays an important role in podosome formation in macrophages. I showed that WASP bound WIP to form a complex at podosomes and that the knockdown of WIP impairs podosome formation. When WASP binding to WIP was blocked, podosome formation was also impaired. When WASP expression was reduced by small interfering RNA transfection, the amount of the complex of WASP with WIP decreased, resulting in reduced podosome formation. Podosomes were restored by reconstitution of the WASP-WIP complex in WASP knockdown cells. These results indicate that the WASP-WIP complex is required for podosome formation in macrophages. When podosome formation was reduced by blocking WASP binding to WIP, transendothelial migration of macrophages, the most crucial process in macrophage trafficking, was impaired. These results suggest that a complex of WASP with WIP plays a critical role in podosome formation, thereby mediating efficient transendothelial migration of macrophages.

Wiskott-Aldrich syndrome protein is a key regulator of the phagocytic cup formation in macrophages.

Phagocytosis is a vital first-line host defense mechanism against infection involving the ingestion and digestion of foreign materials such as bacteria by specialized cells, phagocytes. For phagocytes to ingest the foreign materials, they form an actin-based membrane structure called phagocytic cup at the plasma membranes. Formation of the phagocytic cup is impaired in phagocytes from patients with a genetic immunodeficiency disorder, Wiskott-Aldrich syndrome (WAS). The gene defective in WAS encodes Wiskott-Aldrich syndrome protein (WASP). Mutation or deletion of WASP causes impaired formation of the phagocytic cup, suggesting that WASP plays an important role in the phagocytic cup formation. However, the molecular details of its formation remain unknown. We have shown that the WASP C-terminal activity is critical for the phagocytic cup formation in macrophages. We demonstrated that WASP is phosphorylated on tyrosine 291 in macrophages, and the WASP phosphorylation is important for the phagocytic cup formation. In addition, we showed that WASP and WASP-interacting protein (WIP) form a complex at the phagocytic cup and that the WASP.WIP complex plays a critical role in the phagocytic cup formation. Our results indicate that the phosphorylation of WASP and the complex formation of WASP with WIP are the essential molecular steps for the efficient formation of the phagocytic cup in macrophages, suggesting a possible disease mechanism underlying phagocytic defects and recurrent infections in WAS patients.

A complex of Wiskott-Aldrich syndrome protein with mammalian verprolins plays an important role in monocyte chemotaxis.

The Wiskott-Aldrich syndrome protein (WASP) is a product of the gene defective in an Xid disorder, Wiskott-Aldrich syndrome. WASP expression is limited to hemopoietic cells, and WASP regulates the actin cytoskeleton. It has been reported that monocytes/macrophages from WASP-deficient Wiskott-Aldrich syndrome patients are severely defective in chemotaxis, resulting in recurrent infection. However, the molecular basis of such chemotactic defects is not understood. Recently, the WASP N-terminal region was found to bind to the three mammalian verprolin homologs: WASP interacting protein (WIP); WIP and CR16 homologous protein (WICH)/WIP-related protein (WIRE); and CR16. Verprolin was originally found to play an important role in the regulation of actin cytoskeleton in yeast. We have shown that WASP, WIP, and WICH/WIRE are expressed predominantly in the human monocyte cell line THP-1 and that WIP and WICH/WIRE are involved in monocyte chemotaxis. When WASP binding to verprolins was blocked, chemotactic migration of monocytes was impaired in both THP-1 cells and primary human monocytes. Increased expression of WASP and WIP enhanced monocyte chemotaxis. Blocking WASP binding to verprolins impaired cell polarization but not actin polymerization. These results indicate that a complex of WASP with mammalian verprolins plays an important role in chemotaxis of monocytes. Our results suggest that WASP and mammalian verprolins function as a unit in monocyte chemotaxis and that the activity of this unit is critical to establish cell polarization. In addition, our results also indicate that the WASP-verprolin complex is involved in other functions such as podosome formation and phagocytosis.

Wiskott-Aldrich syndrome protein is involved in alphaIIb beta3-mediated cell adhesion.

The Wiskott-Aldrich syndrome (WAS) is an X-chromosome-linked immunodeficiency disorder. The most common symptom seen in WAS patients is bleeding. One of the main causes of bleeding is defective platelet aggregation. The causative gene of WAS encodes WAS protein (WASP). Here, we show that WASP binds to the calcium- and integrin-binding protein (CIB) in platelets. CIB was originally identified as a protein binding to the alphaIIb cytoplasmic tail of platelet integrin alphaIIb beta3, which has a primary role in platelet aggregation. We also show that the WASP-CIB complex is important in alphaIIb beta3-mediated cell adhesion, and that in patients mutant forms of WASP are expressed at reduced levels or show lower affinities for CIB than wild-type WASP. Our results indicate that impaired complex formation between mutant WASPs and CIB reduces alphaIIb beta3-mediated cell adhesion and causes defective platelet aggregation, resulting in bleeding.

Calcium integrin-binding protein activates platelet integrin alpha IIbbeta 3.

alpha(IIb)beta(3), a platelet-specific integrin, plays a critical role in platelet aggregation. The affinity of alpha(IIb)beta(3) for its ligands such as fibrinogen and von Willebrand factor is tightly regulated in an uncharacterized intracellular process termed inside-out signaling. Calcium integrin-binding protein (CIB) has been identified as a protein interacting with the cytoplasmic tail of the alpha(IIb) subunit of alpha(IIb)beta(3), but its physiological role has not been defined. In the present study, I demonstrate that CIB activates alpha(IIb)beta(3) both in vitro and in vivo. CIB interacts directly with the alpha(IIb) cytoplasmic tail, thereby increasing the affinity of alpha(IIb)beta(3) for fibrinogen in an in vitro fibrinogen-binding assay. The interaction of CIB with the alpha(IIb) cytoplasmic tail is enhanced in a Ca(2+)-dependent manner. A physiological agonist, ADP, stimulates platelets, activating alpha(IIb)beta(3). When the interaction of CIB with the alpha(IIb) cytoplasmic tail is blocked in native platelets by a permeable competing peptide, alpha(IIb)beta(3) activation is not detected even in the presence of ADP. This result indicates that direct interaction of CIB with the alpha(IIb) cytoplasmic tail converts alpha(IIb)beta(3) from a resting to an active conformation. This suggests that CIB plays an important role in one of the pathways that modulate the affinity of alpha(IIb)beta(3) for its ligand.