Tiziana Crepaldi

C-terminal truncated forms of Met, the hepatocyte growth factor receptor.

The MET proto-oncogene encodes a transmembrane tyrosine kinase of 190 kDa (p190MET), which has recently been identified as the receptor for hepatocyte growth factor/scatter factor. p190MET is a heterodimer composed of two disulfide-linked chains of 50 kDa (p50 alpha) and 145 kDa (p145 beta). We have produced four different monoclonal antibodies that are specific for the extracellular domain of the Met receptor. These antibodies immunoprecipitate with p190MET two additional Met proteins of 140 and 130 kDa. The first protein (p140MET) is membrane bound and is composed of an alpha chain (p50 alpha) and an 85-kDa C-terminal truncated beta chain (p85 beta). The second protein (p130MET) is released in the culture supernatant and consists of an alpha chain (p50 alpha) and a 75-kDa C-terminal truncated beta chain (p75 beta). Both truncated forms lack the tyrosine kinase domain. p140MET and p130MET are consistently detected in vivo, together with p190MET, in different cell lines or their culture supernatants. p140MET is preferentially localized at the cell surface, where it is present in roughly half the amount of p190MET. The two C-terminal truncated forms of the Met receptor are also found in stable transfectants expressing the full-length MET cDNA, thus showing that they originate from posttranslational proteolysis. This process is regulated by protein kinase C activation. Together, these data suggest that the production of the C-terminal truncated Met forms may have a physiological role in modulating the Met receptor function.

Effect of hepatocyte growth factor on assembly of zonula occludens-1 protein at the plasma membrane.

Hepatocyte growth factor (HGF) is a paracrine cytokine that influences epithelial morphogenesis by modulating cell–cell adhesion and cell polarity. We have examined the role of HGF in the tight junction (TJ) formation. We followed the assembly and disassembly at the plasma membrane of the major component of the TJ, zonula occludens‐1 (ZO‐1) protein, after HGF treatment. We applied HGF to the basolateral compartment of MDCK cell monolayers grown on transwell filters to analyze the effect of HGF on polarized cells. Confocal laser scanning microscopy showed that HGF caused a marked reduction of ZO‐1 at the lateral sites and a concomitant increase in the cytoplasm. We used the calcium switch assay to analyze the effect of HGF in early TJ development. In MDCK cells cultured in low calcium levels, ZO‐1 is distributed intracellularly. The presence of HGF greatly retarded the movement of ZO‐1 from the cytosol to the membrane after restoration of normal (1.8 mM) calcium levels for 1.5 and 3 hr. The presence of HGF during the calcium switch caused increased tyrosine phosphorylation of β‐catenin. The incubation of MDCK cells with vanadate, a potent tyrosine‐specific phosphatase inhibitor, also affected the ZO‐1 localization at the plasma membrane during the calcium switch. This was concomitant with increased tyrosine phosphorylation of β‐catenin. These results suggest that HGF affects the TJ assembly, and this phenomenon may be important in loosening of intercellular junctions and migration of epithelial cells during HGF‐induced morphogenesis. J. Cell. Physiol. 176:465–471, 1998.

RNAi technology and lentiviral delivery as a powerful tool to suppress Tpr-Met-mediated tumorigenesis

Tpr-Met, the oncogenic counterpart of the Met receptor, has been detected in gastric cancers, as well as in precursor lesions and in the adjacent normal gastric mucosa. This has prompted the suggestion that Tpr-Met may predispose to the development of gastric tumors. Given the sequence specificity of RNA interference, oncogenes activated by point mutation or rearrangements can be targeted while spearing the product of the wild-type allele. In this work, we report specific suppression of Tpr-Met expression and inhibition of Tpr-Met-mediated transformation and tumorigenesis by means of a short interfering RNA (siRNA) directed toward the Tpr-Met junction (anti-TM2). When delivered by a lentiviral vector, anti-TM2 siRNA was effective also in mouse embryonal fibroblasts or epithelial cells expressing high levels of Tpr-Met. Our results suggest that lentiviral-mediated delivery of anti-TM2 siRNA may be developed into a powerful tool to treat Tpr-Met-positive cancers.

Analysis of Mlc-lacZ Met mutants highlights the essential function of Met for migratory precursors of hypaxial muscles and reveals a role for Met in the development of hyoid arch-derived facial muscles

The Pax3 and c‐met genes are necessary for the development of tongue, diaphragm, and limb muscles. These hypaxial muscles derive from precursors that migrate out of the ventrolateral lip of the somites at occipital, cervical, and limb levels. In this work, we re‐examined primary myogenesis in c‐met signaling mutants using a skeletal muscle‐specific lacZ transgene (Mlc3f‐nlacZ‐2E). This strategy allowed us to identify precisely the shoulder, limb, tongue, and dermal muscles that need Met for development and to confirm that the morphological structure of epaxial and body wall muscles was normal, even in the most severe c‐met mutant. Surprisingly, however, X‐gal staining showed that, in this mutant, hyoid arch‐derived facial muscles were either reduced or absent, thus revealing that Met also contributes to the development of muscles in the head. Developmental Dynamics 231:582–591, 2004.

Hepatocyte Growth Factor-mediated satellite cells niche perturbation promotes development of distinct sarcoma subtypes

Embryonal Rhabdomyosarcoma (ERMS) and Undifferentiated Pleomorphic Sarcoma (UPS) are distinct sarcoma subtypes. Here we investigate the relevance of the satellite cell (SC) niche in sarcoma development by using Hepatocyte Growth Factor (HGF) to perturb the niche microenvironment. In a Pax7 wild type background, HGF stimulation mainly causes ERMS that originate from satellite cells following a process of multistep progression. Conversely, in a Pax7 null genotype ERMS incidence drops, while UPS becomes the most frequent subtype. Murine EfRMS display genetic heterogeneity similar to their human counterpart. Altogether, our data demonstrate that selective perturbation of the SC niche results in distinct sarcoma subtypes in a Pax7 lineage-dependent manner, and define a critical role for the Met axis in sarcoma initiation. Finally, our results provide a rationale for the use of combination therapy, tailored on specific amplifications and activated signaling pathways, to minimize resistance emerging from sarcomas heterogeneity. DOI: http://dx.doi.org/10.7554/eLife.12116.001

Bortezomib-mediated proteasome inhibition as a potential strategy for the treatment of rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood, divided into two major histological subtypes, embryonal (ERMS) and alveolar (ARMS). To explore the possibility that the proteasome could be a target of therapeutic value in rhabdomyosarcoma, we treated several RMS cell lines with the proteasome inhibitor bortezomib (Velcade or PS-341) at a concentration of 13-26 nM. RMS cells showed high sensitivity to the drug, whereas no toxic effect was observed in primary human myoblasts. In both ERMS and ARMS cells bortezomib promoted apoptosis, activation of caspase 3 and 7 and induced a dose-dependent reduction of anchorage-independent growth. Furthermore, bortezomib induced activation of the stress response, cell cycle arrest and the reduction of NF-kappaB transcriptional activity. Finally, bortezomib decreased tumour growth and impaired cells viability, proliferation and angiogenesis in a xenograft model of RMS. In conclusion, our data indicate that bortezomib could represent a novel drug against RMS tumours.

Agonist antibodies activating the Met receptor protect cardiomyoblasts from cobalt chloride-induced apoptosis and autophagy.

Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF), mainly activates prosurvival pathways, including protection from apoptosis. In this work, we investigated the cardioprotective mechanisms of Met activation by agonist monoclonal antibodies (mAbs). Cobalt chloride (CoCl2), a chemical mimetic of hypoxia, was used to induce cardiac damage in H9c2 cardiomyoblasts, which resulted in reduction of cell viability by (i) caspase-dependent apoptosis and (ii) – surprisingly – autophagy. Blocking either apoptosis with the caspase inhibitor benzyloxycarbonyl-VAD-fluoromethylketone or autophagosome formation with 3-methyladenine prevented loss of cell viability, which suggests that both processes contribute to cardiomyoblast injury. Concomitant treatment with Met-activating antibodies or HGF prevented apoptosis and autophagy. Pro-autophagic Redd1, Bnip3 and phospho-AMPK proteins, which are known to promote autophagy through inactivation of the mTOR pathway, were induced by CoCl2. Mechanistically, Met agonist antibodies or HGF prevented the inhibition of mTOR and reduced the flux of autophagosome formation. Accordingly, their anti-autophagic function was completely blunted by Temsirolimus, a specific mTOR inhibitor. Targeted Met activation was successful also in the setting of low oxygen conditions, in which Met agonist antibodies or HGF demonstrated anti-apoptotic and anti-autophagic effects. Activation of the Met pathway is thus a promising novel therapeutic tool for ischaemic injury.

Novel therapy for myocardial infarction: can HGF/Met be beneficial?

Myocardial infarction (MI) is a leading cause of hospitalization worldwide. A recently developed strategy to improve the management of MI is based on the use of growth factors which are able to enhance the intrinsic capacity of the heart to repair itself or regenerate after damage. Among others, hepatocyte growth factor (HGF) has been proposed as a modulator of cardiac repair of damage due to the pleiotropic effects elicited by Met receptor stimulation. In this review we describe the mechanistic basis for autocrine and paracrine protection of HGF in the injured heart. We also analyse the role of HGF/Met in stem cell maintenance and in stem cell therapies for MI. Finally, we summarize the most significant results on the use of HGF in experimental models of heart injury and discuss the potential of the molecule for treating ischaemic heart disease in humans.

Conditional Activation of MET in Differentiated Skeletal Muscle Induces Atrophy

Skeletal muscle atrophy is a common debilitating feature of many systemic diseases, including cancer. Here we examined the effects of inducing expression of an oncogenic version of the Met receptor (Tpr-Met) in terminally differentiated skeletal muscle. A responder mouse containing the Tpr-Met oncogene and GFP (green fluorescent protein) as a reporter was crossed with a transactivator mouse expressing tTA under the control of the muscle creatine kinase promoter. Tpr-Met induction during fetal development and in young adult mice caused severe muscle wasting, with decreased fiber size and loss of myosin heavy chain protein. Concomitantly, in the Tpr-Met-expressing muscle the mRNA of the E3 ubiquitin ligases atrogin-1/MAFbx, MuRF1, and of the lysosomal protease cathepsin L, which are markers of skeletal muscle atrophy, was significantly increased. In the same muscles phosphorylation of the Met downstream effectors Akt, p38 MAPK, and IκBα was higher than in normal controls. Induction of Tpr-Met in differentiating satellite cells derived from the double transgenics caused aberrant cell fusion, protein loss, and myotube collapse. Increased phosphorylation of Met downstream effectors was also observed in the Tpr-Met-expressing myotubes cultures. Treatment of these cultures with either a proteasomal or a p38 inhibitor prevented Tpr-Met-mediated myotube breakdown, establishing accelerated protein degradation consequent to inappropriate activation of p38 as the major route for the Tpr-Met-induced muscle phenotype.

Signaling to cardiac hypertrophy: insights from human and mouse RASopathies

Cardiac hypertrophy is the heart’s response to a variety of extrinsic and intrinsic stimuli, some of which might finally lead up to a maladaptive state. An integral part of the pathogenesis of the hypertrophic cardiomyopathy disease (HCM) is the activation of the rat sarcoma (RAS)/RAF/MEK (mitogen-activated protein kinase kinase)/MAPK (mitogen-activated protein kinase) cascade. Therefore, the molecular signaling involving RAS has been the subject of intense research efforts, particularly after the identification of the RASopathies. These constitute a class of developmental disorders caused by germline mutations affecting proteins contributing to the RAS pathway. Among other phenotypic features, a subset of these syndromes is characterized by HCM, prompting researchers and clinicians to delve into the chief signaling constituents of cardiac hypertrophy. In this review, we summarize current advances in the knowledge of the molecular signaling events involved in the pathogenesis of cardiac hypertrophy through work completed on patients and on genetically manipulated animals with HCM and RASopathies. Important insights are drawn from the recognition of parallels between cardiac hypertrophy and cancer. Future research promises to further elucidate the complex molecular interactions responsible for cardiac hypertrophy, possibly pointing the way for the identification of new specific targets for the treatment of HCM.