The molecular architecture of focal adhesions

This article outlines the present knowledge of the architecture, molecular composition, and dynamics of focal contacts of adhesive animal cells. These structures, developed at the plasma membrane at sites where cells touch their substratum, are essential for cellular attachment in tissue formation during embryogenesis and wound healing. In tissue culture, they are particularly prominent and thus amenable to detailed investigation. Focal contacts consist of a cytoplasmic face, comprising cytoskeletal elements, a transmembrane connecting region, and a extracellular face composed of proteins of the extracellular matrix. The molecular anatomy of the numerous proteins involved, the basis for classifying them as structural or regulatory components, and their in vitro interactions are described. Based on this information, current models on the dynamics of their assembly and of possible regulatory mechanisms involving a variety of signal transduction pathways are discussed.

The proline-rich focal adhesion and microfilament protein VASP is a ligand for profilins

Profilins are small proteins that form complexes with G-actin and phosphoinositides and are therefore considered to link the microfilament system to signal transduction pathways. In addition, they bind to poly-L-proline, but the biological significance of this interaction is not yet known. The recent molecular cloning of the vasodilator-stimulated phosphoprotein (VASP), an established in vivo substrate of cAMP- and cGMP-dependent protein kinases, revealed the presence of a proline-rich domain which prompted us to investigate a possible interaction with profilins. VASP is a microfilament and focal adhesion associated protein which is also concentrated in highly dynamic regions of the cell cortex. Here, we demonstrate that VASP is a natural proline-rich profilin ligand. Human platelet VASP bound directly to purified profilins from human platelets, calf thymus and birch pollen. Moreover, VASP and a novel protein were specifically extracted from total cell lysates by profilin affinity chromatography and subsequently eluted either with poly-L-proline or a peptide corresponding to a proline-rich VASP motif. Finally, the subcellular distributions of VASP and profilin suggest that both proteins also interact within living cells. Our data support the hypothesis that profilin and VASP act in concert to convey signal transduction to actin filament formation.

A new functional Ras antagonist inhibits human pancreatic tumor growth in nude mice

Constitutively active Ras proteins, their regulatory components, and overexpressed tyrosine kinase receptors that activate Ras, are frequently associated with cell transformation in human tumors. This suggests that functional Ras antagonists may have anti-tumor activity. Studies in rodent fibroblasts have shown that S-trans, transfarnesylthiosalicylic acid (FTS) acts as a rather specific nontoxic Ras antagonist, dislodging Ras from its membrane anchorage domains and accelerating its degradation. FTS is not a farnesyltransferase inhibitor, and does not affect Ras maturation. Here we demonstrate that FTS also acts as a functional Ras antagonist in human pancreatic cell lines that express activated K-Ras (Panc-1 and MiaPaCa-2). In Panc-1 cells, FTS at a concentration of 25-100 microM reduced the amount of Ras in a dose-dependent manner and interfered with serum-dependent and epidermal growth factor-stimulated ERK activation, thus inhibiting both anchorage-dependent and anchorage-independent growth of Panc-1 cells in vitro. FTS also inhibited tumor growth in Panc-1 xenografted nude mice, apparently without systemic toxicity. Daily FTS treatment (5 mg/kg intraperitoneally) in mice with tumors (mean volume 0.07 cm3) markedly decreased tumor growth (after treatment for 18 days, tumor volume had increased by only 23+/-30-fold in the FTS-treated group and by 127+/-66-fold in controls). These findings suggest that FTS represents a new class of functional Ras antagonists with potential therapeutic value.

Growth factor-dependent activation of the Ras-Raf-MEK-MAPK pathway in the human pancreatic carcinoma cell line PANC-1 carrying activated K-ras: implications for cell proliferation and cell migration

Human ductal adenocarcinoma of the pancreas frequently carry activating point mutations in the K-ras protooncogene. We have analysed the activity of the Ras-Raf-MEK-MAPK cascade in the human pancreatic carcinoma cell line PANC-1 carrying an activating K-ras mutation. Serum-starved cells and cells grown in medium with serum did not show constitutively activated c-Raf, MEK-1, or p42 MAPK. Stimulation of cells with epidermal growth factor (EGF) or fetal calf serum (FCS) resulted in activation of N-Ras, but not K-Ras, as well as activation of c-Raf, MEK-1, and p42 MAPK. Preincubation of serum-starved cells with MEK-1 inhibitor PD98059 abolished EGF- and FCS-induced MAPK activation, identifying MEK as the upstream activator of MAPK. PANC-1 cells exhibited marked serum-dependence of anchorage-dependent and -independent cell growth as well as cell migration. EGF, alone or in combination with insulin and transferrin, did not induce cell proliferation of serum-starved PANC-1 cells, indicating that activation of MAPK alone was not sufficient to induce cell proliferation. FCS-induced DNA synthesis was inhibited by 40% by the MEK-1 inhibitor. On the other hand, treatment with either FCS or EGF alone resulted in marked, MEK-dependent increase of directed cell migration. Collectively, our results show that the activating K-ras mutation in PANC-1 cells does not result in constitutively increased Raf-MEK-MAPK signaling. Signal transduction via the Ras-Raf-MEK-MAPK cascade is maintained in these cells and is required for growth factor-induced cell proliferation and directed cell migration. Oncogene (2000).

TGFbeta1 represses proliferation of pancreatic carcinoma cells which correlates with Smad4-independent inhibition of ERK activation

Transforming growth factor beta (TGFbeta) is a tumor suppressor acting as inhibitor of cell cycle progression of epithelial cells. We show that treatment of the pancreatic carcinoma cell lines PANC-1 and BxPC-3 with TGFbeta1 inhibits both growth factor-induced activation of the extracellular signal-regulated kinase 2 (ERK2) and translocation of the kinase to the nucleus. TGFbeta1 causes a concentration-dependent reduction of cell proliferation in both cell lines. By measuring ERK activation, we can show that TGFbeta1 is able to repress ERK activation induced by mitogenic stimuli such as EGF. This inhibitory effect of TGFbeta1 is not mediated by suppression of Ras or c-Raf-1 activation, but mediated by TGFbeta1-induced activation of a serine-threonine phosphatase, as demonstrated by inhibition of phosphatases by treatment with okadaic acid. Results obtained in the Smad4-deficient pancreatic carcinoma cell line BxPC-3, demonstrate that TGFbeta1-induced growth inhibition is mediated by a Smad4-independent prevention of ERK2 activation. In contrast to the effects of TGFbeta1 on epithelial cells, mesenchymal NIH3T3 fibroblasts exhibit elevated ERK2 activation and increased cell proliferation in response to TGFbeta1 treatment. Smad4-independent phosphatase-mediated inhibition of mitogen-activated ERK2 represents a novel effector pathway contributing to suppression of epithelial pancreatic carcinoma cell proliferation by TGFbeta1, in addition to the well-known Smad-induced tumor suppressor activity of TGFbeta. Oncogene (2000) 19, 4531 - 4541.

Expression of MTA1 promotes motility and invasiveness of PANC-1 pancreatic carcinoma cells

The human metastasis-associated protein 1 (MTA1) is a constituent of the nucleosome-remodelling and -deacetylation complex. Its expression has been correlated with the invasion and metastasis of epithelial neoplasms. To address the functional consequences of MTA1 expression in pancreatic carcinoma cells, we have established PANC-1 pancreatic carcinoma cells that stably express MTA1 as an enhanced green fluorescent fusion protein (EGFP-MTA1). Here, we demonstrate that heterologous expression of EGFP-MTA1 markedly enhanced the cellular motility and the invasive penetration of epithelial barriers by the cells. Expression of EGFP-MTA1 had no effect on substrate-independent growth, but reduced substrate-dependent cell proliferation. In addition, the organisation of the cytokeratin filament system and the localisation of the actin cytoskeleton-associated protein IQGAP1 were distinctly altered in EGFP-MTA1-expressing cells. These results indicate that enhanced expression of MTA1 promotes the acquisition of an invasive, metastatic phenotype, and thus enhances the malignancy of pancreatic adenocarcinoma cells by modulation of the cytoskeleton.

Interaction of plant profilin with mammalian actin

The mode of interaction of birch and bovine profilins with actin was compared using a number of techniques. Birch profilin was purified from pollen or as a recombinant protein from Escherichia coli, using poly(L-proline) affinity chromatography and a monoclonal antibody for the identification of the isolated product. On two-dimensional gels, the genuine and recombinant proteins were identical in molecular mass and isoelectric point and revealed that birch profilin, in contrast to the basic profilins found in mammals, is an acidic protein, analogous to maize profilins. Bovine profilin was obtained from calf thymus. In viscometric assays, the birch protein was seen to modulate actin filament formation analogous to animal profilin. Birch profilin increased the critical concentration required for muscle and brain actin polymerization in a concentration-dependent manner, supporting the notion of the formation of a heterologous complex between the plant protein and animal actin. The effect was Mg(2+)-sensitive, as had been described for homologous complexes. The dissociation constants obtained for the plant/vertebrate and the vertebrate/vertebrate system were both in the micromolar range. The affinity of birch profilin for muscle actin was slightly lower than that for nonmuscle (brain) actin. A binary complex of birch profilin and skeletal muscle actin could be isolated by gel chromatography. Cross-linking experiments with actin, birch profilin, the G-actin binding peptide thymosin beta 4 and gelsolin segment 1, the N-terminal fragment of an actin capping protein, showed that profilin competed with thymosin beta 4, but had no effect on segment 1 binding to actin. These data indicate that the actin-binding domains in plant and animal profilins are functionally highly conserved, although the overall sequence similarity is less than 25%.

Molecular and structural analysis of a continuous birch profilin epitope defined by a monoclonal antibody

The interaction of a mouse monoclonal antibody (4A6) and birch profilin, a structurally well conserved actin- and phosphoinositide-binding protein and cross-reactive allergen, was characterized. In contrast to serum IgE from allergic patients, which shows cross-reactivity with most plants, monoclonal antibody 4A6 selectively reacted with tree pollen profilins. Using synthetic overlapping peptides, a continuous hexapeptide epitope was identified. The exchange of a single amino acid (Gln-47 --> Glu) within the epitope was found to abolish the binding of monoclonal antibody 4A6 to other plant profilins. The NMR analyses of the birch and the nonreactive timothy grass profilin peptides showed that the loss of binding was not due to major structural differences. Both peptides adopted extended conformations similar to that observed for the epitope in the x-ray crystal structure of the native birch profilin. Binding studies with peptides and birch profilin mutants generated by in vitro mutagenesis demonstrated that the change of Gln-47 to acidic amino acids (e.g. Glu or Asp) led to electrostatic repulsion of monoclonal antibody 4A6. In conclusion the molecular and structural analyses of the interaction of a monoclonal antibody with a continuous peptide epitope, recognized in a conformation similar to that displayed on the native protein, are presented.

Plant profilin induces actin polymerization from actin : beta-thymosin complexes and competes directly with beta-thymosins and with negative co-operativity with DNase I for binding to actin

Recombinant plant (birch) profilin was analyzed for its ability to promote actin polymerization from the actin:thymosin beta4 and beta9 complex. Depending on the nature of the divalent cation, recombinant plant (birch) profilin exhibited two different modes of interaction with actin, like mammalian profilin. In the presence of magnesium ions birch profilin promoted the polymerization of actin from A:Tbeta4. In contrast, in the presence of calcium but absence of magnesium ions birch profilin was unable to initiate the polymerization of actin from the complex with Tbeta4. However, under these conditions profilin formed a stable stoichiometric complex with skeletal muscle alpha-actin, as verified by its ability to increase the critical concentration of actin polymerization. Chemical cross-linking indicated that birch profilin competes with Tbeta4 for actin binding. Ternary complex formation of birch profilin with actin:DNase I complex was suggested by chemical cross-linking. However, the determination of the critical concentrations of actin polymerization in the simultaneous presence of birch profilin and DNase I indicated that profilin and DNase I did not form a ternary complex. These data indicated a negative co-operativity between the profilin and DNase I binding sites on actin.

Hepatocyte growth factor and fibroblast growth factor 2 are overexpressed after cerulein-induced acute pancreatitis

The regenerative process after acute inflammation of the pancreas is characterized by cell proliferation as well as synthesis and transient deposition of extracellular matrix. Although the regulation of these processes is still unknown, there is growing evidence that the coordinated activity of various growth factors plays an important role in regeneration. Cerulein-induced pancreatitis in the rat was used to analyze whether growth factors and their receptor concentrations are changed in the acute pancreatitis. Messenger RNA hybridization revealed an individual expression pattern for each analyzed growth factor. The mRNA levels of platelet-derived growth factor B (PDGF B), epidermal growth factor (EGF), and insulin-like growth factor 2 (IGF-2) were not altered, whereas fibroblast growth factor-1 (FGF-1) and 2, IGF-1, transforming growth factor-alpha (TGFalpha), and hepatocyte growth factor (HGF) showed markedly increased concentrations with different expression maxima and duration compared with mRNA levels in healthy pancreata. The FGF-2 and IGF-1 expressions were increased between 1 and 3 days after induction of pancreatitis with maxima at day 2. HGF and FGF-1 mRNAs were upregulated between days 3 and 5. In contrast, TGFalpha exhibited the most prolonged overexpression. In the corresponding receptors, only c-met, the HGF-binding protein, showed higher mRNA and protein levels, whereas the expression of the other receptors did not change. Furthermore, in cultured pancreatic epithelial cells, HGF stimulated the expression of its own receptor in an autocrine manner. These results point out that the highly coordinated process of regeneration after pancreatitis may be influenced by a sequential induction and expression of peptide growth factors and their receptors.

Transforming growth factor-beta-induced upregulation of transforming growth factor-beta receptor expression in pancreatic regeneration

The transforming growth factor-beta (TGFbeta) signaling pathway is one important player in the regulation of extracellular matrix turnover and cell proliferation in epithelial regeneration. We used cerulein-induced pancreatitis in rats as a model to investigate the regulation of TGFbeta receptor type I and type II expression on protein and messenger RNA level during regeneration. In the regenerating pancreas, mRNA levels of TGFbeta receptor I and II were significantly increased with a maximum after 2 days. On protein level, expression of TGFbeta receptor II was significantly increased after three to 3-5 days. This elevated expression could be inhibited by neutralizing the endogenous biological activity of TGFbeta1 with a specific antibody. In cultured pancreatic epithelial cells, TGFbeta1 reduced cell proliferation as measured by [3H]thymidine incorporation. Furthermore the transcript levels of TGFbeta1 as well as mRNA and protein concentrations of type I and type II receptor increased during TGFbeta stimulation in vitro. These results indicate that epithelial pancreatic cells contribute to the enhanced TGFbeta1 synthesis during pancreatic regeneration by an autocrine mechanism. TGFbeta1, furthermore, upregulates the expression of its own receptors during the regenerative process, thereby contributing to the increase of the TGFbeta-induced cellular responses.

CUTL1 promotes tumor cell migration by decreasing proteasome-mediated Src degradation

Recently, we identified the homeodomain transcription factor CUTL1 as important mediator of cell migration and tumor invasion downstream of transforming growth factor beta (TGFbeta). The molecular mechanisms and effectors mediating the pro-migratory and pro-invasive phenotype induced by CUTL1 have not been elucidated so far. Therefore, the aim of this study was to identify signaling pathways downstream of CUTL1 which are responsible for its effects on tumor cell migration. We found that the reduced motility seen after knock down of CUTL1 by RNA interference is accompanied by a delay in tumor cell spreading. This spreading defect is paralleled by a marked reduction of Src protein levels. We show that CUTL1 leads to Src protein stabilization and activation of Src-regulated downstream signaling molecules such as RhoA, Rac1, Cdc42 and ROCK. In addition, we demonstrate that CUTL1 decreases proteasome-mediated Src protein degradation, possibly via transcriptionally upregulating C-terminal Src kinase (Csk). Based on experiments using Src knockout cells (SYF), we present evidence that Src plays a crucial role in CUTL1-induced tumor cell migration. In conclusion, our findings linking the pro-invasive transcription factor CUTL1 and the Src pathway provide important new insights in the molecular effector pathways mediating CUTL-induced migration and invasion.

Burden of itch in ichthyosis: a multicentre study in 94 patients

BACKGROUND

From clinical experience, we know that itch is a major concern for many ichthyosis patients. Nonetheless, no previous studies specifically addressed the issue of itch in ichthyosis.

OBJECTIVE

The objective of this study was to specifically address the burden of itch and all its dimensions in ichthyosis patients.

METHODS

Ninety-four ichthyosis patients from four different centres were recruited to participate in this cross-sectional, questionnaire-based study. All participants completed the Leuven Itch Scale, a multidimensional self-report instrument that quantifies the frequency, duration, severity, distress, consequences and surface area of itch.

RESULTS

Participants included 18 keratinopathic types, 55 autosomal recessive congenital ichthyoses, 11 X-linked recessive ichthyoses (XLRIs), 6 Netherton's ichthyoses, 1 Sjögren-Larsson type, 1 Iocrin ichthyosis and 2 unknown subtypes. Itch occurred in 93% of all patients. In patients with itch, 63% reported that it was often or always present, although most itch episodes were short in duration. Itch, in all its dimensions, was worst in patients with Netherton syndrome. Patients with XLRI had in general a lower itch profile. About half of all ichthyosis patients reported to experience flares during a change in weather, in a hot environment or in stressful situations, whereas a cold environment led to itch in only 26% of patients. The most significant consequences of itching were lesions from scratching, difficulties in falling asleep, bad mood and loss of concentration.

CONCLUSIONS

Itch is a major concern in patients with ichthyosis, with significant impact on daily life. Research on future treatments should therefore take itch into consideration and itch should be evaluated in clinical studies. Among the studied subgroups, Netherton patients experienced the most severe consequences.

Somatostatin-mRNA expression in brainstem projections into the medial preoptic nucleus

The medial preoptic nucleus plays an important role in the regulation of neuroendocrine processes, vegetative functions, sexual behaviour and the modulation of the somatomotoric system. The connections of the medial preoptic nucleus to other areas of the central nervous system are very complex, and the area receives afferents using numerous transmitters and neuropeptides. Previous investigations have shown that this nucleus receives afferents from various brainstem nuclei that also contain somatostatinergic neurons. This study was carried out to investigate if somatostatin-projecting neurons of the brainstem are afferents to the medial preoptic nucleus. This was approached by combining somatostatin-mRNA in situ hybridisation with True Blue retrograde tracing. Our results demonstrate somatostinergic brainstem projections into the medial preoptic nucleus mainly in the pedunculopontine nucleus and in the nucleus of the solitary tract (50% together). Other important somatostatinergic afferents into the medial preoptic nucleus originate in the cuneiform area, the dorsal parabrachial nucleus and in the lateral reticular nucleus (37% together). Less important are the somatostatinergic projections coming from the central grey, the laterodorsal tegmental nucleus, the locus coeruleus and the nucleus raphe magnus. Considering that these areas are involved in diverse functions such as cardiovascular regulation (nucleus of the solitary tract), transmission of visceral sensibility (dorsal parabrachial nucleus), modulation of the somatomotoric system (pedunculopontine nucleus) and in the regulation of neuroendocrine mechanisms (locus coeruleus), it seems tenable that the somatostatin projections demonstrated here also have a diverse functional quality within the medical preoptic nucleus where they terminate.

Birch pollen profilin: structural organization and interaction with poly-(L-proline) peptides as revealed by NMR

The secondary structure of birch pollen profilin, a potent human allergen, was elucidated by multidimensional nuclear magnetic resonance (NMR), as a prerequisite to study the interaction of this profilin with ligands for its poly-(L-proline) (PLP)-binding site. The chemical shifts of the 15N-labeled backbone amide groups were used to monitor complex formation with various PLP peptides. Titration with deca-L-proline (P10) yielded a KD of 0.2 mM. P8 was the shortest PLP to provoke a significant reaction. (GP5)3G bound significantly, confirming the interaction between profilins and the protein VASP containing this motif. Birch profilin interacted also with GP6GP5, found in the cyclase-associated protein (CAP), a suspected profilin ligand.

Signalling processes involved in C-peptide-induced chemotaxis of CD4-positive lymphocytes

Previous data from our group demonstrated that C-peptide induces chemotaxis of CD4-positive lymphocytes in-vitro, mediated by activation of G-protein and PI 3-kinase gamma, but additional signalling pathways involved in this process remained unexplored. In the present study we further analyze intracellular signalling pathways which lead to C-peptide-induced CD4-positive lymphocyte migration. We provide evidence that C-peptide-induced chemotaxis of CD4-positive lymphocytes is critically dependent on activation of Src-kinase and RhoA, Rac-1 and Cdc42 GTPases. Furthermore, C-peptide stimulates phosphorylation of PAK, LIMK and cofilin downstream of Rac-1 and Cdc42, leading to cofilin inactivation and actin filament stabilization. In addition, C-peptide induces ROCK kinase activity and MLC phosphorylation downstream of RhoA, thereby stimulating myosin mediated cell contraction. In contrast, C-peptide does not activate ERK1/2, p38 or Akt in CD4-positive lymphocytes. Our data support an active role of C-peptide in CD4-positive lymphocyte chemotaxis and elucidate molecular mechanisms in C-peptide-induced cell migration.

[Palmoplantar dermatoses: when should genes be considered?]

BACKGROUND

Palmoplantar dermatoses are common. They can be both functionally debilitating and markedly stigmatize the patient because they are so visible. Dermatoses on the hands and feet often go along with palmoplantar hyperkeratosis. Such palmoplantar keratoses (PPK) can be classified into acquired (non-hereditary) and hereditary (monogenetic) PPK.

OBJECTIVES

A considerable proportion of PPK develop on the grounds of gene defects. As these diseases constitute a heterogeneous group of quite uncommon single entities, the treating physician must know when to entertain the diagnosis of a hereditary PPK and which causative genes should be considered.

METHODS

We summarize the common causes of acquired and hereditary PPK based on a review of the latest literature.

RESULTS

The most common causes of acquired PPK are inflammatory dermatoses like psoriasis, lichen planus, or hand and feet eczema. Also irritative-toxic (arsenic poisoning, polycyclic aromatic hydrocarbons) and infectious causes of PPK (human papilloma viruses, syphilis, scabies, tuberculosis, mycoses) are not uncommon. Genetically caused PPK may occur isolated, within syndromes or as a paraneoplastic marker. The clinical/histological classification discerns diffuse, focal, or punctuate forms of PPK with and without epidermolysis. A new classification based on the causative gene defect is starting to replace the traditional clinical classification.

CONCLUSIONS

Knowledge about the large, but heterogeneous group of hereditary PPK is important to adequately counsel and treat patients and their families.

[Palmoplantar dermatoses in children]

Dermatoses of the hands and feet cover a wide range of skin diseases that can occur in children and adolescents and are a frequent question in dermatological practice. Our synopsis of the most important differential diagnoses and their treatment is intended to provide better orientation for daily practice. A precise and detailed history is essential to establish a diagnosis, followed by clinical examination and specific examination methods. Cutaneous infection should always be excluded, as they occur very frequently. Impetigo, punctate keratolysis, blistering distal dactylitis, tinea manuum and pedum, hand-foot-mouth disease, herpes simplex digitalis and verrucae vulgaris as well as scabies are often found in the palmoplantar area and typically affect children and adolescents. In case of allergic contact dermatitis and dyshidrotic eczema, atopic diathesis in the medical history is of importance. However, we must not miss rare causes. Palmoplantar keratoses, for example, can be due to inflammatory dermatoses like pityriasis rubra pilaris (PRP) or may, as well as blistering diseases, result from hereditary disorders. Specialised centers can perform molecular genetic diagnosis and enhance patient care.