Pain-related threat and coordination in adults with chronic low back pain during a lifting task: A cross-sectional study.

OBJECTIVES: People with low back pain (LBP) exhibit altered coordination, possibly indicating guarded movement. The connection between these changes and pain-related threat remains unclear. We aimed to determine if pain-related threat was related to spinal coordination and variability, during a lifting task, in people with chronic LBP. METHODS: Participants were adults with chronic LBP (n = 47). Upper lumbar, lower lumbar, and hipkinematics were measured during 10crate lifting/lowering repetitions. Coordination and variability of the Hip-Lower Lumbar, and Lower Lumbar-Upper Lumbar joint pairs were calculated. Pain-related threat was measured using the Tampa Scale for Kinesiophobia, the Pain Catastrophizing Scale, and task-specific fear. Linear regression analyses tested the relationship between pain-related threat and coordination. RESULTS: Adding catastrophizing to our base model (sex) explained variance in Hip-Lower lumbar coordination (r2 change = 0.125, p = 0.013). General and task specific measures of fear were unrelated to coordination and variability at both joint pairs (r2 change < 0.064, p > 0.05). Exploratory t-tests revealed subgroups aligned with phenotypes of "tight" and "loose" control, where "tight" control was characterized by greater catastrophizing and disability. CONCLUSION: Pain catastrophizing, but not measures of fear, was related to more in-phase ("tight") Hip-Lower Lumbar coordination during lifting/lowering. Considering this relationship based on subgroups may add clarity.

Gait risk factors for disease progression differ between non-traumatic and post-traumatic knee osteoarthritis.

OBJECTIVE: To examine if relationships between knee osteoarthritis (OA) progression with knee moments and muscle activation during gait vary between patients with non-traumatic and post-traumatic knee OA. DESIGN: This longitudinal study included participants with non-traumatic (n = 17) and post-traumatic (n = 18) knee OA; the latter group had a previous anterior cruciate ligament rupture. Motion capture cameras, force plates, and surface electromyography measured knee moments and lower extremity muscle activation during gait. Cartilage volume change were determined over 2 years using magnetic resonance imaging in four regions: medial and lateral plateau and condyle. Linear regression analysis examined relationships between cartilage change with gait metrics (moments, muscle activation), group, and their interaction. RESULTS: Measures from knee adduction and rotation moments were related to lateral condyle cartilage loss in both groups, and knee adduction moment to lateral plateau cartilage loss in the non-traumatic group only [ß = -1.336, 95% confidence intervals (CI) = -2.653 to -0.019]. Generally, lower levels of stance phase muscle activation were related to greater cartilage loss. The relationship between cartilage loss in some regions with muscle activation characteristics varied between non-traumatic and post-traumatic groups including for: lateral hamstring (lateral condyle ß = 0.128, 95%CI = 0.003 to 0.253; medial plateau ß = 0.199, 95%CI = 0.059 to 0.339), rectus femoris (medial condyle ß = -0.267, 95%CI = -0.460 to -0.073), and medial hamstrings (medial plateau; ß = -0.146, 95%CI = -0.244 to -0.048). CONCLUSION: Findings indicate that gait risk factors for OA progression may vary between patients with non-traumatic and post-traumatic knee OA. These OA subtypes should be considered in studies that investigate gait metrics as risk factors for OA progression.

Inter-joint coordination and the flexion-relaxation phenomenon among adults with low back pain during bending.

BACKGROUND: Altered inter-joint coordination and reduced flexion-relaxation at end-range trunk flexion are common in people with low back pain. Inconsistencies in these behaviors, however, make assessment and treatment challenging for this population. RESEARCH QUESTION: The study objective was to investigate patterns of regional lumbo-pelvic coordination and flexion-relaxation in adults with and without low back pain, during a bending task. METHODS: Adults with low back pain (n = 16) and a healthy group (n = 21) performed three trials of a bending task. Motion capture and surface electromyography systems measured joint kinematics (hip, lower and upper lumbar spine) and muscle activity (erector spinae longissimus, iliocostalis, and multifidus). Continuous relative phase analysis determined inter-joint coordination of the hip/lower lumbar and lower lumbar/upper lumbar joint pairs, during flexion and extension periods. Flexion-relaxation ratios using normalized surface electromyography data determined the extent of flexion-relaxation for each muscle, during each period. For inter-joint coordination, two-way repeated measure mixed ANOVAs calculated the effects of group (healthy/low back pain), period, and their interactions. Separate hierarchical linear models were constructed and tested relationships between flexion-relaxation ratios and our independent variables, group and muscle, while controlling for patient characteristics. RESULTS: The low back pain group had more out-of-phase coordination of the hip/lower lumbar joint pair compared to the healthy group (mean difference = 24.7°; 95 % confidence interval = 3.93-45.4), independent of movement period. No significant between group differences in lower lumbar/upper lumbar coordination were observed. The low back pain group demonstrated reduced flexion-relaxation of all muscles during full flexion (21.7 % reduction on average), with multifidus showing the least relaxation. SIGNIFICANCE: Regional differences in the lumbar spine and the possibility of subgroups with distinct movement pattern should be considered when analyzing coordination in people with low back pain. Multifidus showed the largest changes in flexion-relaxation and should be included when measuring this construct.

Lower-limb coordination and variability during gait: The effects of age and walking surface.

BACKGROUND: Falls among community-dwelling older adults are often triggered by uneven walkways. Joint coordination and its variability change with age and may place older adults at risk of falling. It is unclear how irregular surfaces impact lower-limb joint coordination and if such changes are exacerbated by aging. RESEARCH QUESTION: To what extent do lower-limb inter-joint coordination and its variability, over flat and uneven brick walkways, differ between older and young healthy adults? METHODS: A motion-capture system collected kinematic data from walking trials on flat and uneven walkways in seventeen older (72.0 ±â€¯4.2 years) and eighteen younger (27.0 ±â€¯4.7 years) healthy adults. Continuous relative phase analyses were performed for the Knee-Hip and Ankle-Knee joint pairs. Mean Absolute Relative Phase (MARP) quantified coordination amplitude. Deviation Phase (DP) quantified coordinative variability. Two-way mixed ANOVA's tested for effects of age, surface, and age × surface interactions. RESULTS: Uneven surfaces prompted more in-phase MARP inter-joint coordination in adults during most gait phases (p ≤ 0.024). Age × surface interactions were observed during initial contact (Ankle-Knee: p = 0.021, Knee-Hip: p = 0.001) and loading response (Knee-Hip: p = 0.017), with post-hoc analyses showing coordination accentuated in older adults. Uneven surfaces induced higher DP in Knee-Hip (p = 0.017) and Ankle-Knee joint coupling (p < 0.001) during gait, largely independent of age. An age × surface interaction was observed during mid-swing (p = 0.050), with post-hoc analysis revealing increased variability in older adults. SIGNIFICANCE: More in-phase and variable lower-limb gait behavior was observed on uneven walkways. These differences were accentuated in older adults during early stance phase (more tightly coordinated) and mid-swing (more variable). This may reflect a cautious gait strategy on challenging walkways to maintain stability and help prevent falls.

A comparison of muscle activation and knee mechanics during gait between patients with non-traumatic and post-traumatic knee osteoarthritis.

OBJECTIVE: The objective was to compare muscle activation and knee mechanics during gait between participants with non-traumatic knee osteoarthritis (OA), post-traumatic knee OA, and healthy adults. DESIGN: Participants with non-traumatic knee OA (n = 22), post-traumatic knee OA (n = 19), and healthy adults (n = 22) completed gait trials for this observational, cross-sectional study. Post-traumatic OA group had a history of traumatic anterior cruciate ligament (ACL) rupture. Surface electromyography (EMG) measured activation of seven lower extremity muscles. Motion capture cameras and force plates measured motion and force data. Principal component analysis (PCA) determined waveform characteristics (principal components) from EMG, knee angle, and knee external moment waveforms. Analysis of variance (ANOVA) examined group differences in principal component scores (PC-scores). Regression analyses examined if a variable that coded for OA group could predict PC-scores after accounting for disease severity, alignment, and lateral OA. RESULTS: There was lower gastrocnemius EMG amplitudes (P < 0.01; ANOVA) in the post-traumatic OA group compared to healthy group. Non-traumatic OA group had higher vastus lateralis, vastus medialis, and rectus femoris EMG compared to post-traumatic OA group (P = 0.01 to 0.04) in regression analyses. Also, non-traumatic OA group had higher and prolonged lateral hamstring EMG compared to healthy (P = 0.03; ANOVA) and post-traumatic OA (P = 0.04; regression) groups respectively. The non-traumatic OA group had lower knee extension (P < 0.05) and medial rotation (P < 0.05) moments than post-traumatic and healthy groups. CONCLUSIONS: Muscle activation and knee mechanics differed between participants with non-traumatic and post-traumatic knee OA and healthy adults. These OA subtypes had differences in disease characteristics that may impact disease progression.

Relationship between alignment and cartilage thickness in patients with non-traumatic and post-traumatic knee osteoarthritis.

OBJECTIVE: To compare cartilage thickness between patients with non-traumatic and post-traumatic knee osteoarthritis (OA) and healthy controls and to determine if disease severity and alignment impact these differences. DESIGN: Participants with non-traumatic (n = 22) and post-traumatic (n = 19) knee OA, and healthy controls (n = 22) were recruited for this cross-sectional study. Participants underwent 3T magnetic resonance imaging (T1-weighted, 3D sagittal gradient echo sequence) and cartilage thickness was determined in four regions: medial and lateral condyle, and medial and lateral plateau. Lower extremity alignment (mechanical axis angle) and disease severity (Kellgren-Lawrence scores) were measured from full length radiographs. Statistical analysis included one-way analysis of variance (ANOVA) and modified Bonferroni test adjusting for multiple pairwise comparisons. Linear regression analyses examined the relationship between cartilage thickness and knee OA group after controlling for disease severity, meniscal status, and alignment. RESULTS: In participants with predominantly medial compartment knee OA, compared to healthy controls, those with non-traumatic knee OA had diminished cartilage thickness in the medial plateau (p = 0.035) and those with post-traumatic knee OA had greater cartilage thickness in the lateral condyle (p = 0.044). In the lateral condyle, data revealed that alignment accounted for the variance in cartilage thickness (p = 0.035), in which a stronger relationship was found in the non-traumatic (r = -0.61) than the post-traumatic (r = -0.12) OA group. CONCLUSIONS: Emerging data demonstrated that participants with non-traumatic knee OA have a stronger relationship between alignment and cartilage thickness than those with post-traumatic knee OA. This indicates that factors involved in knee OA initiation and progression may differ between these OA subtypes.

The Role of Neurotrophin Signaling in Gliomagenesis: A Focus on the p75 Neurotrophin Receptor (p75NTR/CD271).

The p75 neurotrophin receptor (p75NTR, a.k.a. CD271), a transmembrane glycoprotein and a member of the tumor necrosis family (TNF) of receptors, was originally identified as a nerve growth factor receptor in the mid-1980s. While p75NTR is recognized to have important roles during neural development, its presence in both neural and nonneural tissues clearly supports the potential to mediate a broad range of functions depending on cellular context. Using an unbiased in vivo selection paradigm for genes underlying the invasive behavior of glioma, a critical characteristic that contributes to poor clinical outcome for glioma patients, we identified p75NTR as a central regulator of glioma invasion. Herein we review the expanding role that p75NTR plays in glioma progression with an emphasis on how p75NTR may contribute to the treatment refractory nature of glioma. Based on the observation that p75NTR is expressed and functional in two critical glioma disease reservoirs, namely, the highly infiltrative cells that evade surgical resection, and the radiation- and chemotherapy-resistant brain tumor-initiating cells (also referred to as brain tumor stem cells), we propose that p75NTR and its myriad of downstream signaling effectors represent rationale therapeutic targets for this devastating disease. Lastly, we provide the provocative hypothesis that, in addition to the well-documented cell autonomous signaling functions, the neurotrophins, and their respective receptors, contribute in a cell nonautonomous manner to drive the complex cellular and molecular composition of the brain tumor microenvironment, an environment that fuels tumorigenesis.

Glioma invasion mediated by the p75 neurotrophin receptor (p75(NTR)/CD271) requires regulated interaction with PDLIM1.

The invasive nature of glioblastoma renders them incurable by current therapeutic interventions. Using a novel invasive human glioma model, we previously identified the neurotrophin receptor p75(NTR) (aka CD271) as a mediator of glioma invasion. Herein, we provide evidence that preventing phosphorylation of p75(NTR) on S303 by pharmacological inhibition of PKA, or by a mutational strategy (S303G), cripples p75(NTR)-mediated glioma invasion resulting in serine phosphorylation within the C-terminal PDZ-binding motif (SPV) of p75(NTR). Consistent with this, deletion (ΔSPV) or mutation (SPM) of the PDZ motif results in abrogation of p75(NTR)-mediated invasion. Using a peptide-based strategy, we identified PDLIM1 as a novel signaling adaptor for p75(NTR) and provide the first evidence for a regulated interaction via S425 phosphorylation. Importantly, PDLIM1 was shown to interact with p75(NTR) in highly invasive patient-derived glioma stem cells/tumor-initiating cells and shRNA knockdown of PDLIM1 in vitro and in vivo results in complete ablation of p75(NTR)-mediated invasion. Collectively, these data demonstrate a requirement for a regulated interaction of p75(NTR) with PDLIM1 and suggest that targeting either the PDZ domain interactions and/or the phosphorylation of p75(NTR) by PKA could provide therapeutic strategies for patients with glioblastoma.

Osteoarthritis year in review 2014: rehabilitation and outcomes.

OBJECTIVE: To highlight research studies examining rehabilitation for hip and knee osteoarthritis (OA), as well as the outcome measures used to assess treatment efficacy, published in 2013. DESIGN: A systematic search was performed in Medline, CIHAHL and Embase databases from January to December 2013. The search was limited to 2013, human studies, and English. Rehabilitation intervention studies included were prospective controlled designs. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to evaluate the quality of evidence. First, individual articles were rated for quality. Second, articles were grouped based on outcome: OA disease markers, pain, physical function (self-reported, performance), and health. RESULTS: Of 503 titles reviewed, 36 studies were included. The outcome measures related to OA disease markers were organized into subthemes of anthropometrics, biomechanics and physiology. The quality of evidence was of moderate, high, and low quality for anthropometric, biomechanical and physiological measures respectively. These studies supported the use of diet for weight loss combined with exercise. Bodies of evidence that showed the efficacy of exercise and passive strategies (thermal/electrical modalities, traction, manual therapy) for reducing pain were of low and moderate quality respectively. The evidence supporting diet and exercise, physiotherapy, and passive strategies to improve physical function was of moderate quality. Evidence supporting exercise to improve psychological factors was of moderate quality. CONCLUSIONS: Exercise combined with diet for weight loss should be the mainstays of rehabilitation for people with knee and hip OA to provide benefit to OA disease markers, pain, physical function, and health.

Comparison of measurement properties of the P4 pain scale and disease specific pain measures in patients with knee osteoarthritis.

OBJECTIVE: To compare measurement properties of the P4 pain scale, Western Ontario and McMaster Universities Arthritis Index pain subscale (WOMAC-pain), and Intermittent and Constant Osteoarthritis Pain (ICOAP) measure in patients with knee osteoarthritis (OA). DESIGN: A secondary analysis from a randomized controlled trial included participants (n = 156) with knee OA that were consulting with a surgeon regarding knee arthroplasty. They completed pain measures (P4, WOMAC-pain, ICOAP) and WOMAC-function subscale (WOMAC-function) at baseline and 2 weeks. Measurement properties assessed in various subgroups included floor/ceiling effects, test-retest reliability using intraclass correlation coefficients (ICC2,1), internal consistency using Cronbach's ɑ, factorial structure of each pain measure combined with WOMAC-function using principal component analysis, and responsiveness using standardized response mean (SRM). RESULTS: P4 had low floor and ceiling effects (<1%). P4 test-retest reliability (ICC2,1 = 0.72), internal consistency (Chronbach's ɑ = 0.91), and responsiveness (SRM = 0.56) were similar to the values for WOMAC-pain and ICOAP. Factorial structure of P4 and ICOAP were separate from WOMAC-function items. WOMAC-pain and WOMAC-function items loaded on similar factors. ICOAP-constant subscale had a large floor effect (33%). CONCLUSIONS: P4 should be used to measure pain in patients with knee OA. It had acceptable measurement properties which is comparable to more widely used pain measures. WOMAC-pain shared a factorial structure with WOMAC-function indicating these measures might be capturing the same construct, questioning its validity to measure pain separately from function. ICOAP had acceptable properties. More work should compare pain measures in less severely affected OA populations.

Ephrin A5 expression promotes invasion and transformation of murine fibroblasts.

Emerging evidence suggests involvement of the ephrin/Eph receptor system in tumourigenesis. Research on this new role has centred on the contribution of Eph receptors. In contrast, we focused on the elucidation of the role of ephrins, specifically ephrin A5. Results indicated an increase in invasive potential of ephrin A5-expressing murine fibroblasts, which was abolished by addition of a Src family kinase inhibitor. Furthermore, anchorage-independent growth was increased in ephrin A5-expressing cells. Stimulation with EphA5-Fc receptor increased colony size, but not colony number in ephrin A5 transfectants. Moreover, we observed morphogenetic transformation of ephrin A5-expressing 3T3 cells into a branching network when plated onto Matrigel. This behaviour was specific to ephrin A5 transfectants, as 3T3 cells expressing ephrin B1 displayed a phenotype similar to control 3T3 cells. We conclude that ectopic expression of ephrin A5 in murine fibroblasts elevates oncogenic potential, including increased invasive behaviour, anchorage-independent growth, and morphological transformation.

Differential activation of ERKs to focal adhesions by PKC epsilon is required for PMA-induced adhesion and migration of human glioma cells.

Protein kinase C (PKC) is a family of serine/threonine kinases involved in the transduction of a variety of signals. There is increasing evidence to indicate that specific PKC isoforms are involved in the regulation of distinct cellular processes. In glioma cells, PKC alpha was found to be a critical regulator of proliferation and cell cycle progression, while PKC epsilon was found to regulate adhesion and migration. Herein, we report that specific PKC isoforms are able to differentially activate extracellular-signal regulated kinase (ERK) in distinct cellular locations: while PKC alpha induces the activation of nuclear ERK, PKC epsilon induces the activation of ERK at focal adhesions. Inhibition of the ERK pathway completely abolished the PKC-induced integrin-mediated adhesion and migration. Thus, we present the first evidence that PKC epsilon is able to activate ERK at focal adhesions to mediate glioma cell adhesion and motility, providing a molecular mechanism to explain the different biological functions of PKC alpha and epsilon in glioma cells.

Lipopolysaccharide-stimulated or granulocyte-macrophage colony-stimulating factor-stimulated monocytes rapidly express biologically active IL-15 on their cell surface independent of new protein synthesis.

Although IL-15 shares many of the biological activities of IL-2, IL-2 expression is primarily under transcriptional regulation, while the mechanisms involved in the regulation of IL-15 are complex and not completely understood. In the current study, we found that CD14(+) monocytes constitutively exhibit both IL-15 mRNA and protein. IL-15 protein was found stored intracellularly and stimulation of CD14(+) monocytes with either LPS or GM-CSF resulted in mobilization of IL-15 stores to the plasma membrane. This rapidly induced surface expression was the result of a translocation of preformed stores, confirming that posttranslational regulatory stages limit IL-15, because it was not accompanied by an increase in IL-15 mRNA and occurred independent of de novo protein synthesis. After fixation, activated monocytes, but not resting monocytes, were found to support T cell proliferation, and this effect was abrogated by the addition of an IL-15-neutralizing Ab. The presence of preformed IL-15 stores and the ability of stimulated monocytes to mobilize these stores to their surface in an active form is a novel mechanism of regulation for IL-15.

Anergy and acquired immune deficiency syndrome.

Human immunodeficiency virus (HIV), the retrovirus associated with acquired immune deficiency syndrome (AIDS), acts as a super-antigen by binding to the variable region of the beta (V beta) chain of T-cell receptor (TCR). It's binding to CD4 molecules and chemokine receptors induces a spectrum of immune abnormalities including 'a state of anergy' in the host. This state is due to a defective function of T-helper cell-1 (Th-1), a reduction in production of lymphokines required for signal transduction, an impaired cytotoxic cell activation and a decrease in antigen presenting function of monocyte-macrophage cell lineage. These immune abnormalities form the basis for severe opportunistic infections and malignancies in the host. Malnutrition, micronutrient abnormalities, concomitant infections and genetic factors, etc., are some of the compounding co-factors that further contribute to 'the state of anergy'.

Anergy and human immunodeficiency virus infection.

Human immunodeficiency virus (HIV), the retrovirus associated with acquired immune deficiency syndrome (AIDS), induces a spectrum of immune abnormalities including a state of anergy in the host. This state is due to the binding of HIV envelope glycoprotein moieties to CD4 molecules and chemokine receptors. Resulting decrease in antigen presenting cell function and the interference with functioning of positive and negative regulatory molecules involved in signal transduction have an anergizing effect on the immune system. This effect is exemplified by diminished production of interleukin-2 (IL-2) and interferon-gamma and reduced expression of IL-2 receptor by CD4 helper cells of HIV patients. These immune abnormalities lead to clinically relevant immunological phenomena such as Type-1 to Type-2 switch, decrease in delayed-type hypersensitivity dermal reaction, etc. Insight into these interesting phenomena could pave the path for favorably altering the immunological milieu for drug and vaccine trials.

Mercuric chloride activates the Src-family protein tyrosine kinase, Hck in myelomonocytic cells.

Hck is a member of the Src-family of protein tyrosine kinases that appears to function in mature leukocytes to communicate a number of extracellular signals including various cytokines. In this study we show that the thiol-reactive heavy metal, mercuric chloride (HgCl2) induces rapid and robust activation of tyrosine phosphorylation within human myelomonocytic cells. This increase in tyrosine-phosphorylated proteins requires the activity of Hck because both kinase inactive alleles of Hck and pharmacological inhibitors selective for the Src-family kinases are able to abrogate the cellular response to HgCl2. Furthermore, ectopic expression of Hck in murine fibroblasts is able to confer HgCl2 responsiveness, as indicated by an increase in tyrosine-phosphorylated proteins to a normally nonresponsive cell line. Concomitant with the activation of Hck, there is a physical association of Hck with another cytoplasmic protein tyrosine kinase, Syk. The ability of HgCl2 to activate Src-family kinases such as Hck in hematopoietic cells may help explain why exposure to the heavy metal is associated with immune system dysfunction in rodents as well as humans.

Ephrin-A5 modulates cell adhesion and morphology in an integrin-dependent manner.

The ephrins are membrane-tethered ligands for the Eph receptor tyrosine kinases, which play important roles in patterning of the nervous and vascular systems. It is now clear that ephrins are more than just ligands and can also act as signalling-competent receptors, participating in bidirectional signalling. We have recently shown that ephrin-A5 signals within caveola-like domains of the plasma membrane upon engagement with its cognate Eph receptor, leading to increased adhesion of the cells to fibronectin. Here we show that ephrin-A5 controls sequential biological events that are consistent with its role in neuronal guidance. Activation of ephrin-A5 induces an initial change in cell adhesion followed by changes in cell morphology. Both effects are dependent on the activation of beta1 integrin involving members of the Src family of protein tyrosine kinases. The prolonged activation of ERK-1 and ERK-2 is required for the change in cell morphology. Our work suggests a new role for class A ephrins in specifying the affinity of the cells towards various extracellular substrates by regulating integrin function.

Decreased expression of the INK4 family of cyclin-dependent kinase inhibitors in Wilms tumor.

Cyclin-dependent kinase (CDK) inhibitors represented by the INK4 family (including p16(INK4a, CDKN2A), p15(INK4b, CDKN2B), p18(INK4c, CDKN2C), and p19(INK4d, CDKN2D)) are regulators of the cell cycle shown to be aberrant in many types of human cancer. We tested the hypothesis that these CDK inhibitors are a target for altered gene expression in Wilms tumor. Using RT-PCR, gene expression of the INK4 family was found to be decreased in 9 of 38 Wilms tumor samples obtained from the National Wilms Tumor Study Group (NWTSG) tissue bank. All the affected tumor samples were of favorable histology. Methylation-specific PCR revealed that methylation in the p16 promoter region may be responsible for altered expression. The incidence of loss of p16 expression may increase with increasing tumor stage, i.e., 1/10 (10%) with stage I/II FH Wilms tumor, 2/10 (20%) with stage III FH Wilms tumor, and 4/10 (40%) with stage IV FH Wilms tumor. Thus, determining the expression status of the INK4 family may have potential prognostic value in the management of Wilms tumor.

Signaling within a caveolae-like membrane microdomain in human neuroblastoma cells in response to fibroblast growth factor.

It is now clear that the plasma membrane is not homogeneous but contains specific subcompartments characterized by their unique lipid and protein composition. Based on their enrichment in various signaling molecules, these microcompartments are now recognized to be sites of localized signal transduction for several extracellular stimuli. At least two different types of microdomains can be identified, largely based on the presence or absence of the caveolin proteins. The generic name of caveolae-like domains is commonly used to refer to both domains indistinguishably. Although caveolin proteins were long thought to be absent from the brain, we have shown that the human neuroblastoma cell line LAN-1 expresses both caveolin-1 and caveolin-2. Basic fibroblast growth factor (FGF)-2 induced a specific signaling response within the caveolae-like domain of LAN-1 cells, characterized by the tyrosine phosphorylation of a 75-80-kDa protein. This protein present in the caveolae-like domains has properties suggesting that it is a member of the SNT family of adapter proteins. The signaling event originating in the caveolae-like domains in response to FGF-2 appeared to require the activation of at least Fyn and Lyn, two members of the Src family of tyrosine kinases. This work suggests that compartmentalized signaling within caveolae-like domains may create a level of specificity for certain growth factors such as FGF.

Compartmentalized signaling by GPI-anchored ephrin-A5 requires the Fyn tyrosine kinase to regulate cellular adhesion.

Eph receptor tyrosine kinases and their corresponding surface-bound ligands, the ephrins, provide cues to the migration of cells and growth cones during embryonic development. Here we show that ephrin-A5, which is attached to the outer leaflet of the plasma membrane by a glycosyl-phosphatidylinositol-anchor, induces compartmentalized signaling within a caveolae-like membrane microdomain when bound to the extracellular domain of its cognate Eph receptor. The physiological response induced by this signaling event is concomitant with a change in the cellular architecture and adhesion of the ephrin-A5-expressing cells and requires the activity of the Fyn protein tyrosine kinase. This study stresses the relevance of bidirectional signaling involving the ephrins and Eph receptors during brain development.