Caveolin-1 is required for TGF-ß-induced transactivation of the EGF receptor pathway in hepatocytes through the activation of the metalloprotease TACE/ADAM17.

Transforming growth factor-beta (TGF-ß) plays a dual role in hepatocytes, inducing both pro- and anti-apoptotic responses, whose balance decides cell fate. Survival signals are mediated by the epidermal growth factor receptor (EGFR) pathway, which is activated by TGF-ß in these cells. Caveolin-1 (Cav1) is a structural protein of caveolae linked to TGF-ß receptors trafficking and signaling. Previous results have indicated that in hepatocytes, Cav1 is required for TGF-ß-induced anti-apoptotic signals, but the molecular mechanism is not fully understood yet. In this work, we show that immortalized Cav1(-/-) hepatocytes were more sensitive to the pro-apoptotic effects induced by TGF-ß, showing a higher activation of caspase-3, higher decrease in cell viability and prolonged increase through time of intracellular reactive oxygen species (ROS). These results were coincident with attenuation of TGF-ß-induced survival signals in Cav1(-/-) hepatocytes, such as AKT and ERK1/2 phosphorylation and NFκ-B activation. Transactivation of the EGFR pathway by TGF-ß was impaired in Cav1(-/-) hepatocytes, which correlated with lack of activation of TACE/ADAM17, the metalloprotease responsible for the shedding of EGFR ligands. Reconstitution of Cav1 in Cav1(-/-) hepatocytes rescued wild-type phenotype features, both in terms of EGFR transactivation and TACE/ADAM17 activation. TACE/ADAM17 was localized in detergent-resistant membrane (DRM) fractions in Cav1(+/+) cells, which was not the case in Cav1(-/-) cells. Disorganization of lipid rafts after treatment with cholesterol-binding agents caused loss of TACE/ADAM17 activation after TGF-ß treatment. In conclusion, in hepatocytes, Cav1 is required for TGF-ß-mediated activation of the metalloprotease TACE/ADAM17 that is responsible for shedding of EGFR ligands and activation of the EGFR pathway, which counteracts the TGF-ß pro-apoptotic effects. Therefore, Cav1 contributes to the pro-tumorigenic effects of TGF-ß in liver cancer cells.

Patients' perception and effectiveness of a treatment containing enfuvirtide when used in HIV-infected patients without very advanced disease.

PURPOSE: To evaluate the satisfaction with self-injected enfuvirtide (ENF) and the clinical outcome of HIV-infected patients without very advanced disease. METHOD: ESPPE is a multicenter observational study that included 103 evaluated patients showing baseline characteristics predictive of positive outcome: CD4 >100 cells/mm3, viral load (VL) <100,000 copies/mL, previous treatment with a maximum of 10 antiretroviral drugs, and concomitant use of 2 active drugs. By using validated surveys, patients were questioned 6 months after the prescription of ENF about their quality of life (QoL) and acceptance of self-injections and adherence to the treatment. RESULTS: At 6 months, the mean CD4 increase was 121 cells/mm3 (p < .05) and 65% (intent-to-treat, ENF stopped=failure) had VL <50 copies/mL (p < .001). Fourteen patients discontinued the treatment, mostly due to intolerance (6). The majority (>89%) assessed all items relating QoL as "excellent," "very good," or "good." The treatment satisfaction index on a visual analog scale scored a median of 8.1 out of 10; when participants were asked about the interference of injections on their daily activities, 87% answered "never" or "only sometimes." CONCLUSION: Effectiveness and patients' perception about ENF remain good when ENF was used in patients without very advanced disease. QoL was not impaired after ENF use.

Once-daily antiretroviral therapy: Spanish Consensus Statement.

BACKGROUND: Administration of antiretroviral therapy (ART) once daily is creating extraordinary interest among the members of the scientific community and also among those who receive the therapy. However, in clinical practice, some doubts remain about its use. OBJECTIVES: This document examines the characteristics and possibilities of treatment administered once daily. METHODS: Consensus of 248 Spanish experts in the field. RESULTS: Once-daily dosing is considered an added value which could favour adherence and, therefore, efficacy, as well as the quality of life of certain patients, however, the objective of adequate adherence in the long term is often difficult to achieve regardless of the treatment used. In theory, any patient can receive once-daily therapy, although some patients could particularly benefit from it, e.g. those with unfavourable social or personal circumstances, including drug users, patients whose treatment must be supervised, patients receiving multiple medications, or those who need rescue therapy after multiple treatment failures. At present, it is possible to design once-daily ART using some of the combinations of drugs considered as first-choice in national and international recommendations for antiretroviral therapy, but the options are still limited. The marketing of new drugs with this characteristic could allow us to increase the number and types of patient who can benefit from once-daily regimens, including those patients who need rescue therapy. CONCLUSIONS: Once-daily ART is a good alternative to regimens administered several times each day when a potent combination of active drugs is available.

Integrin regulation of membrane domain trafficking and Rac targeting.

Integrins are crucial regulators of essential cellular processes such as gene expression, cell proliferation and migration. Alteration of these processes is central to tumourigenesis. Integrin signals mediate anchorage dependence of cell growth, while growth of cancer cells is anchorage-independent. Integrins critically regulate Rho family GTPases, that are also involved in cell-cycle progression and oncogenesis. In addition to their effect on GTP loading, integrins independently control the translocation of GTP-bound Rac to the plasma membrane. This step is essential for Rac binding to effectors. Integrins increase membrane affinity for Rac, leading to RhoGDI dissociation and effector coupling locally, in the vicinity of activated/bound integrins. Integrin-regulated Rac binding sites are within CEMMs (cholesterol-enriched membrane microdomains). Integrins control Rac signalling by preventing the internalization of its binding sites in CEMMs. Integrin regulation of signalling pathways initiated in CEMMs may be important for the spatial control of cell migration and anchorage dependence of cell growth.

Distinct functions of Vav1 in JNK1 activation in Jurkat T cells versus non-haematopoietic cells.

Vav1, the 95-kDa protein encoded by the vav1 proto-oncogene, is expressed exclusively in haematopoietic cells, where it becomes phosphorylated on tyrosine residues in response to antigen receptor ligation. Vav1 was found to act as a Rac1-specific guanine nucleotide exchange factor and to activate c-Jun N-terminal kinase (JNK1) in vitro and in ectopic expression systems using non-haematopoietic cells. Here, we studied the role of Vav1 in JNK1 activation in T cells versus non-haematopoietic cells. Vav1 overexpression activated JNK1 in COS7 and 293T cells but not in Jurkat T lymphocytes. In contrast, constitutively activated Rac1 efficiently stimulated JNK1 in both cell types under the same conditions. Vav1 did function in T cells because it clearly stimulated the activity of a nuclear factor of activated T-cell reporter plasmid in the same cells. Moreover, Vav1 induction of JNK1 in T cells required coexpression with calcineurin. This cooperation was cell type specific because it was not observed in COS7 or 293T cells. In contrast, Vav1 did not cooperate with calcineurin to activate either extracellular signal-regulated kinase 2 or p38. These findings demonstrate that Vav1 alone is a poor activator of the JNK1 pathway in T cells and emphasize the importance of studying the physiological functions of Vav1 in haematopoietic cells.

Consensus conference on chronic viral hepatitis and HIV infection: updated Spanish recommendations.

Chronic hepatitis B and C represent a leading cause of morbidity and mortality among human immunodeficiency virus (HIV)-infected patients worldwide. New treatment options against both hepatitis B (HBV) and C (HCV) viruses have prompted us to update previous recommendations for the management of coinfected individuals. Fifteen topics (nine related to HCV, five to HBV and one to both viruses) were selected for this purpose. A panel of Spanish experts in the field was invited to review these areas and propose specific recommendations, which were scored according to the Infectious Disease Society of America (IDSA) grading system. These guidelines represent a comprehensive and updated overview on the management of hepatitis B and C in HIV-infected patients.

Activation of integrins in endothelial cells by fluid shear stress mediates Rho-dependent cytoskeletal alignment.

Fluid shear stress is a critical determinant of vascular remodeling and atherogenesis. Both integrins and the small GTPase Rho are implicated in endothelial cell responses to shear but the mechanisms are poorly understood. We now show that shear stress rapidly stimulates conformational activation of integrin alpha(v)beta3 in bovine aortic endothelial cells, followed by an increase in its binding to extracellular cell matrix (ECM) proteins. The shear-induced new integrin binding to ECM induces a transient inactivation of Rho similar to that seen when suspended cells are plated on ECM proteins. This transient inhibition is necessary for cytoskeletal alignment in the direction of flow. The results therefore define the role of integrins and Rho in a pathway leading to endothelial cell adaptation to flow.

The molecular adapter SLP-76 relays signals from platelet integrin alphaIIbbeta3 to the actin cytoskeleton.

Platelet adhesion to fibrinogen through integrin alpha(IIb)beta(3) triggers actin rearrangements and cell spreading. Mice deficient in the SLP-76 adapter molecule bleed excessively, and their platelets spread poorly on fibrinogen. Here we used human platelets and a Chinese hamster ovary (CHO) cell expression system to better define the role of SLP-76 in alpha(IIb)beta(3) signaling. CHO cell adhesion to fibrinogen required alpha(IIb)beta(3) and stimulated tyrosine phosphorylation of SLP-76. SLP-76 phosphorylation required coexpression of Syk tyrosine kinase and stimulated association of SLP-76 with the adapter, Nck, and with the Rac exchange factor, Vav1. SLP-76 expression increased lamellipodia formation induced by Syk and Vav1 in adherent CHO cells (p < 0.001). Although lamellipodia formation requires Rac, SLP-76 functioned downstream of Rac by potentiating adhesion-dependent activation of PAK kinase (p < 0.001), a Rac effector that associates with Nck. In platelets, adhesion to fibrinogen stimulated the association of SLP-76 with the SLAP-130 adapter and with VASP, a SLAP-130 binding partner implicated in actin reorganization. Furthermore, SLAP-130 colocalized with VASP at the periphery of spread platelets. Thus, SLP-76 functions to relay signals from alpha(IIb)beta(3) to effectors of cytoskeletal reorganization. Therefore, deficient recruitment of specific adapters and effectors to sites of adhesion may explain the integrin phenotype of SLP-76(-/-) platelets.

Adhesion to the extracellular matrix regulates the coupling of the small GTPase Rac to its effector PAK.

The small GTPase Rac regulates cytoskeletal organization, cell cycle progression, gene expression and oncogenic transformation, processes that depend upon both soluble growth factors and adhesion to the extracellular matrix (ECM). We now show that growth factors and adhesion to the ECM both contribute independently and approximately equally to Rac activation. However, activated Rac in non-adherent cells failed to stimulate the Rac effector PAK. V12 Rac or Rac activated by serum translocated to the membrane fraction of adherent cells but remained mainly cytoplasmic in suspended cells. An activated Rac mutant lacking a membrane-targeting sequence did not activate PAK in adherent cells, while mutations that forced membrane targeting restored PAK activation in suspended cells. In vitro, V12 Rac showed greater binding to membranes from adherent relative to suspended cells, indicating that cell adhesion regulated membrane binding sites for Rac. These results show that ECM regulates the ability of Rac to couple with PAK via an effect on membrane binding sites that facilitate their interaction.

Polarization and interaction of adhesion molecules P-selectin glycoprotein ligand 1 and intercellular adhesion molecule 3 with moesin and ezrin in myeloid cells.

In response to the chemoattractants interleukin 8, C5a, N-formyl-methionyl-leucyl-phenylalanine, and interleukin 15, adhesion molecules P-selectin glycoprotein ligand 1 (PSGL-1), intercellular adhesion molecule 3 (ICAM-3), CD43, and CD44 are redistributed to a newly formed uropod in human neutrophils. The adhesion molecules PSGL-1 and ICAM-3 were found to colocalize with the cytoskeletal protein moesin in the uropod of stimulated neutrophils. Interaction of PSGL-1 with moesin was shown in HL-60 cell lysates by isolating a complex with glutathione S-transferase fusions of the cytoplasmic domain of PSGL-1. Bands of 78- and 81-kd were identified as moesin and ezrin by Western blot analysis. ICAM-3 and moesin also coeluted from neutrophil lysates with an anti-ICAM-3 immunoaffinity assay. Direct interaction of the cytoplasmic domains of ICAM-3 and PSGL-1 with the amino-terminal domain of recombinant moesin was demonstrated by protein-protein binding assays. These results suggest that the redistribution of PSGL-1 and its association with intracellular molecules, including the ezrin-radixin-moesin actin-binding proteins, regulate functions mediated by PSGL-1 in leukocytes stimulated by chemoattractants.

Rho GTPases control migration and polarization of adhesion molecules and cytoskeletal ERM components in T lymphocytes.

Motile lymphocytes adopt a polarized morphology with different adhesion molecules (ICAM, CD43 and CD44) and ERM actin-binding proteins concentrated on the uropod, a slender posterior appendage with important functions in cell-cell interactions and lymphocyte recruitment. We have studied the role of Rho family of GTPases (Rho, Rac and Cdc42) in the control of lymphocyte polarity and migration by analyzing the effects of exogenously introduced Rho GTPase mutants. Transfection of T cell lines that constitutively display a polarized motile morphology with activated mutants of RhoA, Rac1 and Cdc42 impaired cell polarization. A guanosine nucleotide exchange factor for Rac, Tiam-1, induced the same effect as activated Rac1. Conversely, dominant negative forms of the three GTP-binding proteins induced a polarized phenotype in constitutively round-shaped T cells with redistribution of ICAM-3 and moesin to the uropod in an integrin-dependent manner. On the other hand, overexpression of dominant negative Cdc42 and activated mutants of all three Rho GTPases significantly inhibited SDF-1alpha-induced T cell chemotaxis. Together, these data demonstrate that Rho GTPases regulate lymphocyte polarization and chemokine-induced migration, and underscore the key role of Cdc42 in lymphocyte directional migration.

Involvement of phosphatidylinositol 3-kinase in stromal cell-derived factor-1 alpha-induced lymphocyte polarization and chemotaxis.

The role of phosphatidylinositol 3-kinase (PI3-kinase), an important enzyme involved in signal transduction events, has been studied in the polarization and chemotaxis of lymphocytes induced by the chemokine stromal cell-derived factor-1 alpha (SDF-1 alpha). This chemokine was able to directly activate p85/p110 PI3-kinase in whole human PBL and to induce the association of PI3-kinase to the SDF-1 alpha receptor, CXCR4, in a pertussis toxin-sensitive manner. Two unrelated chemical inhibitors of PI3-kinase, wortmannin and Ly294002, prevented ICAM-3 and ERM protein moesin polarization as well as the chemotaxis of PBL in response to SDF-1 alpha. However, they did not interfere with the reorganization of either tubulin or the actin cytoskeleton. Moreover, the transient expression of a dominant negative form of the PI3-kinase 85-kDa regulatory subunit in the constitutively polarized Peer T cell line inhibited ICAM-3 polarization and markedly reduced SDF-1 alpha-induced chemotaxis. Conversely, overexpression of a constitutively activated mutant of the PI3-kinase 110-kDa catalytic subunit in the round-shaped PM-1 T cell line induced ICAM-3 polarization. These results underline the role of PI3-kinase in the regulation of lymphocyte polarization and motility and indicate that PI3-kinase plays a selective role in the regulation of adhesion and ERM proteins redistribution in the plasma membrane of lymphocytes.

Leukocyte polarization in cell migration and immune interactions.

Cell migration plays a key role in a wide variety of biological phenomena. This process is particularly important for leukocyte function and the inflammatory response. Prior to migration leukocytes undergo polarization, with the formation of a lamellipodium at the leading edge and a uropod at the trailing edge. This cell shape allows them to convert cytoskeletal forces into net cell-body displacement. Leukocyte chemoattractants, including chemokines, provide directional cues for leukocyte motility, and concomitantly induce polarization. Chemoattractant receptors, integrins and other adhesion molecules, cytoskeletal proteins and intracellular regulatory molecules change their cellular localization during cell polarization. A complex system of signal transduction molecules, including tyrosine kinases, lipid kinases, second messengers and members of the Rho family of small GTPases is thought to regulate the cytoskeletal rearrangements underlying leukocyte polarization and migration. The elucidation of the mechanisms and signals that control this complex reorganization will lead to a better understanding of critical questions in cell biology of leukocyte migration and polarity.

Interferon alpha treatment of chronic hepatitis C in HIV-infected patients receiving zidovudine: efficacy, tolerance and response related factors.

BACKGROUND/AIMS: In our area most of the human immunodeficiency virus (HIV) infected patients are intravenous drug users; HIV and hepatitis C virus infections often coexist in these patients. Due to the repercussions of both infections, we designed a trial to evaluate the efficacy, response-related factors and tolerance during an eight-month regime of recombinant interferon alpha-2b on hepatitis C virus infection. METHODOLOGY: We included 79 patients in an open, prospective and multicentric trial with zidovudine and interferon alpha-2b. Response to interferon treatment was evaluated by biochemical and histopathological criteria. RESULTS: A complete response (alanine aminotransferase normalization) was obtained in 57.4% of patients. The significant response-related factors were: degree of histopathological activity, CD4+ cell number and initial leukocyte number. CONCLUSIONS: Recombinant interferon therapy seems to be effective for chronic hepatitis C in HIV infected patients; the best response was in those with active chronic hepatitis and CD4+ cell counts > or = 200/mm3. General tolerance was variable, although side effects were not different from those seen in non-HIV patients. The most common side effect was flu-like syndrome (constitutional manifestations), with no interference on treatment continuity; however, hematological toxicity prevents the indiscriminate use of interferon.

The two poles of the lymphocyte: specialized cell compartments for migration and recruitment.

Chemotaxis, the directed migration of leukocytes towards a chemoattractant gradient, is a key phenomenon in the immune response. During lymphocyte-endothelial and -extracellular matrix interactions, chemokines induce the polarization of T lymphocytes, with generation of specialized cell compartments. The chemokine receptors involved in detection of the chemoattractant gradients concentrate at the leading edge (advancing front or anterior pole) of the cell. The adhesion molecules ICAM-1, -3, CD44 and CD43 redistribute to the uropod, an appendage at the posterior pole of migrating T lymphocyte that protrudes from the contact area with endothelial or extracellular matrix substrates. Whereas chemokine receptors sense the direction of migration, the uropod is involved in the recruitment of bystander leukocytes through LFA-1/ICAM-dependent cell-cell interactions. While beta-actin concentrates preferentially at the cell's leading edge, the motor protein myosin II and a microtubule organizing center (MTOC) are packed in the uropod. The actin-binding protein moesin, which belongs to the ERM family of ezrin, radixin and moesin, redistributes to the distal portion of uropods and physically interacts with ICAM-3, CD44 and CD43, thus acting as a physical link between the membrane molecules and the actin cytoskeleton. Moreover, the moesin-ICAM-3 association correlates with the degree of cell polarity. The redistribution of the chemokine receptors and adhesion molecules to opposite poles of the cell in response to a chemoattractant gradient may guide cell migration and cell-cell interactions during lymphoid cell trafficking in immune and inflammatory responses.

Roles of chemokines and receptor polarization in NK-target cell interactions.

We report that the ability of NK cells to produce chemokines is increased in NK-target cell conjugates. The chemokines produced play a critical role in the polarization and recruitment of NK cells as well as in the NK effector-target cell conjugate formation. Chemokines induce the formation of two specialized regions in the NK cell: the advancing front or leading edge, where chemokine receptors CCR2 and CCR5 cluster, which might guide the cells toward the chemotactic source, and the uropod, where adhesion molecules ICAM-1 and -3 are redistributed. NK cell polarity was intrinsically involved in conjugate formation. The redistribution of both adhesion receptors and CCR was preserved during the formation of NK-target cell conjugates. Time-lapse videomicroscopy studies of the formation of effector-target conjugates showed that morphologic poles are also functionally distinct; while the binding to target cells was preferentially mediated through the leading edge, the uropod was found at the rear of migrating NK cells and recruited additional NK cells to the vicinity of K562 target cells. Inhibition of cell polarization and adhesion receptor redistribution blocked the formation of NK-K562 cell conjugates and the cytotoxic activity of NK cells. We discuss the implication of NK-cell polarization in the development of cytotoxic responses.

The chemokine SDF-1alpha triggers a chemotactic response and induces cell polarization in human B lymphocytes.

We studied the expression and possible functional role of chemokine receptors CXCR3, CXCR4 and CCR5 in normal human B lymphocytes. B cells from both peripheral blood and tonsils expressed high levels of CXCR4 but not the other chemokine receptors tested. CXCR4 ligand, stromal cell-derived factor (SDF)-1alpha, elicited a potent chemotactic response and induced a polarized motile phenotype in B cells, resulting in redistribution of the adhesion molecule ICAM-3 to a posterior appendage of the cell, termed uropod, and of CXCR4 receptor to the leading edge of migrating B cells. Time-lapse videomicroscopy studies revealed that SDF-1alpha-treated cells recruited additional bystander B cells through the uropod. SDF-1alpha induced levels of cellular recruitment comparable to those elicited by polarization-inducing anti-ICAM-3 monoclonal antibody, in an LFA-1/ICAM-1, -3-dependent fashion. Moreover, this chemokine increased intracellular Ca2+ levels in B lymphocytes, and induced a rapid CXCR4 receptor down-regulation on the cell surface membrane. These results provide new insight into the important biological role of SDF-1alpha in physiological processes in which B cells participate, and suggest a key role for chemokines in normal B cell trafficking and recirculation.

CD43 interacts with moesin and ezrin and regulates its redistribution to the uropods of T lymphocytes at the cell-cell contacts.

Chemokines as well as the signaling through the adhesion molecules intercellular adhesion molecule (ICAM)-3 and CD43 are able to induce in T lymphocytes their switching from a spherical to a polarized motile morphology, with the formation of a uropod at the rear of the cell. We investigated here the role of CD43 in the regulation of T-cell polarity, CD43-cytoskeletal interactions, and lymphocyte aggregation. Pro-activatory anti-CD43 monoclonal antibody (MoAb) induced polarization of T lymphocytes with redistribution of CD43 to the uropod and the CCR2 chemokine receptor to the leading edge of the cell. Immunofluorescence analysis showed that all three ezrin-radixin-moesin (ERM) actin-binding proteins localized in the uropod of both human T lymphoblasts stimulated with anti-CD43 MoAb and tumor-infiltrating T lymphocytes. Radixin localized at the uropod neck, whereas ezrin and moesin colocalized with CD43 in the uropod. Biochemical analyses showed that ezrin and moesin coimmunoprecipitated with CD43 in T lymphoblasts. Furthermore, in these cells, the CD43-associated moesin increased after stimulation through CD43. The interaction of moesin and ezrin with CD43 was specifically mediated by the cytoplasmic domain of CD43, as shown by precipitation of both ERM proteins with a GST-fusion protein containing the CD43 cytoplasmic tail. Videomicroscopy analysis of homotypic cell aggregation induced through CD43 showed that cellular uropods mediate cell-cell contacts and lymphocyte recruitment. Immunofluorescence microscopy performed in parallel showed that uropods enriched in CD43 and moesin localized at the cell-cell contact areas of cell aggregates. The polarization and homotypic cell aggregation induced through CD43 was prevented by butanedione monoxime, indicating the involvement of myosin cytoskeleton in these phenomena. Altogether, these data indicate that CD43 plays an important regulatory role in remodeling T-cell morphology, likely through its interaction with actin-binding proteins ezrin and moesin. In addition, the redistribution of CD43 to the uropod region of migrating lymphocytes and during the formation of cell aggregates together with the enhancing effect of anti-CD43 antibodies on lymphocyte cell recruitment suggest that CD43 plays a key role in the regulation of cell-cell interactions during lymphocyte traffic.

Moesin interacts with the cytoplasmic region of intercellular adhesion molecule-3 and is redistributed to the uropod of T lymphocytes during cell polarization.

During activation, T lymphocytes become motile cells, switching from a spherical to a polarized shape. Chemokines and other chemotactic cytokines induce lymphocyte polarization with the formation of a uropod in the rear pole, where the adhesion receptors intercellular adhesion molecule-1 (ICAM-1), ICAM-3, and CD44 redistribute. We have investigated membrane-cytoskeleton interactions that play a key role in the redistribution of adhesion receptors to the uropod. Immunofluorescence analysis showed that the ERM proteins radixin and moesin localized to the uropod of human T lymphoblasts treated with the chemokine RANTES (regulated on activation, normal T cell expressed, and secreted), a polarization-inducing agent; radixin colocalized with arrays of myosin II at the neck of the uropods, whereas moesin decorated the most distal part of the uropod and colocalized with ICAM-1, ICAM-3, and CD44 molecules. Two other cytoskeletal proteins, beta-actin and alpha-tubulin, clustered at the cell leading edge and uropod, respectively, of polarized lymphocytes. Biochemical analysis showed that moesin coimmunoprecipitates with ICAM-3 in T lymphoblasts stimulated with either RANTES or the polarization- inducing anti-ICAM-3 HP2/19 mAb, as well as in the constitutively polarized T cell line HSB-2. In addition, moesin is associated with CD44, but not with ICAM-1, in polarized T lymphocytes. A correlation between the degree of moesin-ICAM-3 interaction and cell polarization was found as determined by immunofluorescence and immunoprecipitation analysis done in parallel. The moesin-ICAM-3 interaction was specifically mediated by the cytoplasmic domain of ICAM-3 as revealed by precipitation of moesin with a GST fusion protein containing the ICAM-3 cytoplasmic tail from metabolically labeled Jurkat T cell lysates. The interaction of moesin with ICAM-3 was greatly diminished when RANTES-stimulated T lymphoblasts were pretreated with the myosin-disrupting drug butanedione monoxime, which prevents lymphocyte polarization. Altogether, these data indicate that moesin interacts with ICAM-3 and CD44 adhesion molecules in uropods of polarized T cells; these data also suggest that these interactions participate in the formation of links between membrane receptors and the cytoskeleton, thereby regulating morphological changes during cell locomotion.