Membrane-type 1 Matrix Metalloproteinase Modulates Tissue Homeostasis by a Non-proteolytic Mechanism

Membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14), a transmembrane proteinase with a short cytoplasmic tail, is a major effector of extracellular matrix remodeling. Genetic silencing of MT1-MMP in mouse (Mmp14 ^-/- ) and man causes dwarfism, osteopenia, arthritis, and lipodystrophy, abnormalities ascribed to defective collagen turnover. We have previously shown non-proteolytic functions of MT1-MMP mediated by its cytoplasmic tail, where the unique tyrosine (Y573) controls intracellular signaling. The Y573D mutation blocks TIMP-2/MT1-MMP-induced Erk1/2 and Akt signaling without affecting proteolytic activity. Here, we report that a mouse with the MT1-MMP Y573D mutation (Mmp14 ^Y573D/Y573D ) shows abnormalities similar to but also different from those of Mmp14 ^-/- mice. Skeletal stem cells (SSC) of Mmp14 ^Y573D/Y573D mice show defective differentiation consistent with the mouse phenotype, which is rescued by wild-type SSC transplant. These results provide the first in vivo demonstration that MT1-MMP modulates bone, cartilage, and fat homeostasis by controlling SSC differentiation through a mechanism independent of proteolysis.

Ambra1 spatially regulates Src activity and Src/FAK-mediated cancer cell invasion via trafficking networks

Here, using mouse squamous cell carcinoma cells, we report a completely new function for the autophagy protein Ambra1 as the first described 'spatial rheostat' controlling the Src/FAK pathway. Ambra1 regulates the targeting of active phospho-Src away from focal adhesions into autophagic structures that cancer cells use to survive adhesion stress. Ambra1 binds to both FAK and Src in cancer cells. When FAK is present, Ambra1 is recruited to focal adhesions, promoting FAK-regulated cancer cell direction-sensing and invasion. However, when Ambra1 cannot bind to FAK, abnormally high levels of phospho-Src and phospho-FAK accumulate at focal adhesions, positively regulating adhesion and invasive migration. Spatial control of active Src requires the trafficking proteins Dynactin one and IFITM3, which we identified as Ambra1 binding partners by interaction proteomics. We conclude that Ambra1 is a core component of an intracellular trafficking network linked to tight spatial control of active Src and FAK levels, and so crucially regulates their cancer-associated biological outputs.

Fine-tuning of ULK1 mRNA and protein levels is required for autophagy oscillation

ULK1 is a key kinase in autophagy initiation. Nazio et al. demonstrate that the E3 ubiquitin ligase NEDD4L targets ULK1 for degradation soon after autophagy induction, whereas a simultaneous ULK1 mRNA transcription is needed for priming subsequent rounds of autophagy.

Autophagy is an intracellular degradation pathway whose levels are tightly controlled to secure cell homeostasis. Unc-51–like kinase 1 (ULK1) is a conserved serine–threonine kinase that plays a central role in the initiation of autophagy. Here, we report that upon autophagy progression, ULK1 protein levels are specifically down-regulated by the E3 ligase NEDD4L, which ubiquitylates ULK1 for degradation by the proteasome. However, whereas ULK1 protein is degraded, ULK1 mRNA is actively transcribed. Upon reactivation of mTOR-dependent protein synthesis, basal levels of ULK1 are promptly restored, but the activity of newly synthesized ULK1 is inhibited by mTOR. This prepares the cell for a new possible round of autophagy stimulation. Our results thus place NEDD4L and ULK1 in a key position to control oscillatory activation of autophagy during prolonged stress to keep the levels of this process under a safe and physiological threshold.

Membrane-Type 1 Matrix Metalloproteinase Downregulates Fibroblast Growth Factor-2 Binding to the Cell Surface and Intracellular Signaling

Membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14), a transmembrane proteinase with an extracellular catalytic domain and a short cytoplasmic tail, degrades extracellular matrix components and controls diverse cell functions through proteolytic and non-proteolytic interactions with extracellular, intracellular, and transmembrane proteins. Here we show that in tumor cells MT1-MMP downregulates fibroblast growth factor-2 (FGF-2) signaling by reducing the amount of FGF-2 bound to the cell surface with high and low affinity. FGF-2 induces weaker activation of ERK1/2 MAP kinase in MT1-MMP expressing cells than in cells devoid of MT1-MMP. This effect is abolished in cells that express proteolytically inactive MT1-MMP but persists in cells expressing MT1-MMP mutants devoid of hemopexin-like or cytoplasmic domain, showing that FGF-2 signaling is downregulated by MT1-MMP proteolytic activity. MT1-MMP expression results in downregulation of FGFR-1 and -4, and in decreased amount of cell surface-associated FGF-2. In addition, MT1-MMP strongly reduces the amount of FGF-2 bound to the cell surface with low affinity. Because FGF-2 association with low-affinity binding sites is a prerequisite for binding to its high-affinity receptors, downregulation of low-affinity binding to the cell surface results in decreased FGF-2 signaling. Consistent with this conclusion, FGF-2 induction of tumor cell migration and invasion in vitro is stronger in cells devoid of MT1- MMP than in MT1-MMP expressing cells. Thus, MT1-MMP controls FGF-2 signaling by a proteolytic mechanism that decreases the cell's biological response to FGF-2.

TIMP-2 Interaction with MT1-MMP Activates the AKT Pathway and Protects Tumor Cells from Apoptosis

Membrane-type 1 matrix metalloproteinase (MT1-MMP), a transmembrane proteinase with an extracellular catalytic domain and a short cytoplasmic tail, degrades a variety of extracellular matrix (ECM) components. In addition, MT1-MMP activates intracellular signaling through proteolysis-dependent and independent mechanisms. We have previously shown that binding of tissue inhibitor of metalloproteinases-2 (TIMP-2) to MT1-MMP controls cell proliferation and migration, as well as tumor growth in vivo by activating the Ras—extracellular signal regulated kinase-1 and -2 (ERK1/2) pathway through a mechanism that requires the cytoplasmic but not the proteolytic domain of MT1-MMP. Here we show that in MT1-MMP expressing cells TIMP-2 also induces rapid and sustained activation of AKT in a dose- and time-dependent manner and by a mechanism independent of the proteolytic activity of MT1-MMP. Fibroblast growth factor receptor-1 mediates TIMP-2 induction of ERK1/2 but not of AKT activation; however, Ras activation is necessary to transduce the TIMP-2-activated signal to both the ERK1/2 and AKT pathways. ERK1/2 and AKT activation by TIMP-2 binding to MT1-MMP protects tumor cells from apoptosis induced by serum starvation. Conversely, TIMP-2 upregulates apoptosis induced by three-dimensional type I collagen in epithelial cancer cells. Thus, TIMP-2 interaction with MT1-MMP provides tumor cells with either pro- or anti-apoptotic signaling depending on the extracellular environment and apoptotic stimulus.

Prolonged Pseudohypoxia Targets Ambra1 mRNA to P-Bodies for Translational Repression

Hypoxia has been associated with several pathological conditions ranging from stroke to cancer. This condition results in the activation of autophagy, a cyto-protective response involving the formation of double-membraned structures, the autophagosomes, in the cytoplasm. In this study, we investigated the cellular mechanisms regulating the autophagy gene Ambra1, after exposure to a hypoxia mimetic, cobalt chloride (CoCl2). We observed that, upon CoCl2 administration, activation of the apoptotic machinery was concomitant with down-regulation of the pro-autophagic factor Ambra1, without affecting transcription. Additionally, co-treating the cells with the caspase inhibitor z-VAD-FMK did not restore Ambra1 protein levels, this implying the involvement of other regulatory mechanisms. Partial re-localization of Ambra1 mRNA to non-translating fractions and cytoplasmic P-bodies was further detected. Thus, in this pseudohypoxic context, Ambra1 mRNA translocation to P-bodies and translational suppression correlated with increased cell death.

Autophagy induction impairs migration and invasion by reversing EMT in glioblastoma cells

Cell migration and invasion are highly regulated processes involved in both physiological and pathological conditions. Here we show that autophagy modulation regulates the migration and invasion capabilities of glioblastoma (GBM) cells. We observed that during autophagy occurrence, obtained by nutrient deprivation or by pharmacological inhibition of the mTOR complexes, GBM migration and chemokine-mediated invasion were both impaired. We also observed that SNAIL and SLUG, two master regulators of the epithelial-mesenchymal transition (EMT process), were down-regulated upon autophagy stimulation and, as a consequence, we found a transcriptional and translational up-regulation of N- and R-cadherins. Conversely, in BECLIN 1-silenced GBM cells, an increased migration capability and an up-regulation of SNAIL and SLUG was observed, with a resulting decrease in N- and R-cadherin mRNAs. ATG5 and ATG7 down-regulation also resulted in an increased migration and invasion of GBM cells combined to an up-regulation of the two EMT regulators. Finally, experiments performed in primary GBM cells from patients largely confirmed the results obtained in established cell cultures. Overall, our results indicate that autophagy modulation triggers a molecular switch from a mesenchymal phenotype to an epithelial-like one in GBM cellular models. Since the aggressiveness and lethality of GBM is defined by local invasion and resistance to chemotherapy, we believe that our evidence provides a further rationale for including autophagy/mTOR-based targets in the current therapeutical regimen of GBM patients.

Mitochondrial dynamics protein Drp1 is overexpressed in oncocytic thyroid tumors and regulates cancer cell migration

Oncocytic cell tumors are characterized by the accumulation of morphologically abnormal mitochondria in their cells, suggesting a role for abnormal mitochondrial biogenesis in oncocytic cell transformation. Little is known about the reason for the dysmorphology of accumulated mitochondria. The proteins regulating the morphology of mitochondria, the "mitochondria-shaping" proteins, can modulate their size and number; however, nothing is known hitherto about a possible involvement of mitochondrial dynamics in oncocytic cell transformation in tumors. Our aim was to assess the status of the mitochondria morphology and its role in oncocytic cell transformation. We therefore evaluated the expression pattern of the main mitochondrial fusion and fission proteins in a series of thyroid cell tumor samples, as well as in thyroid tumor cell lines, with and without oncocytic cell features. The expression of mitochondrial fusion (Opa1, Mfn1 and Mfn2) and fission (Drp1 and Fis1) proteins were evaluated by immunohistochemistry (IHC) in a series of 88 human thyroid tumors. In vitro studies, for comparative purposes and to deepen the study, were performed using TPC1 - a papillary thyroid carcinoma derived cell line—and XTC.UC1, an oncocytic follicular thyroid carcinoma-derived cell line. Both IHC and in vitro protein analyses showed an overall increase in the levels of "mitochondrial-shaping" proteins in oncocytic thyroid tumors. Furthermore, overexpression of the pro-fission protein Drp1 was found to be associated with malignant oncocytic thyroid tumors. Interestingly, genetic and pharmacological blockage of Drp1 activity was able to influence thyroid cancer cells’ migration/invasion ability, a feature of tumor malignancy. In this study we show that unbalanced mitochondrial dynamics characterize the malignant features of thyroid oncocytic cell tumors, and participate in the acquisition of the migrating phenotype.

TGF-β1 induces endothelial cell apoptosis by shifting VEGF activation of p38(MAPK) from the prosurvival p38β to proapoptotic p38α

TGF-β1 and VEGF, both angiogenesis inducers, have opposing effects on vascular endothelial cells. TGF-β1 induces apoptosis; VEGF induces survival. We have previously shown that TGF-β1 induces endothelial cell expression of VEGF, which mediates TGF-β1 induction of apoptosis through activation of p38 mitogen-activated protein kinase (MAPK). Because VEGF activates p38(MAPK) but protects the cells from apoptosis, this finding suggested that TGF-β1 converts p38(MAPK) signaling from prosurvival to proapoptotic. Four isoforms of p38(MAPK) -α, β, γ, and δ-have been identified. Therefore, we hypothesized that different p38(MAPK) isoforms control endothelial cell apoptosis or survival, and that TGF-β1 directs VEGF activation of p38(MAPK) from a prosurvival to a proapoptotic isoform. Here, we report that cultured endothelial cells express p38α, β, and γ. VEGF activates p38β, whereas TGF-β1 activates p38α. TGF-β1 treatment rapidly induces p38α activation and apoptosis. Subsequently, p38α activation is downregulated, p38β is activated, and the surviving cells become refractory to TGF-β1 induction of apoptosis and proliferate. Gene silencing of p38α blocks TGF-β1 induction of apoptosis, whereas downregulation of p38β or p38γ expression results in massive apoptosis. Thus, in endothelial cells p38α mediates apoptotic signaling, whereas p38β and p38γ transduce survival signaling. TGF-β1 activation of p38α is mediated by VEGF, which in the absence of TGF-β1 activates p38β. Therefore, these results show that TGF-β1 induces endothelial cell apoptosis by shifting VEGF signaling from the prosurvival p38β to the proapoptotic p38α.

Alternative splicing and tumor progression

Alternative splicing is a key molecular mechanism for increasing the functional diversity of the eukaryotic proteomes. A large body of experimental data implicates aberrant splicing in various human diseases, including cancer. Both mutations in cis-acting splicing elements and alterations in the expression and/or activity of splicing regulatory factors drastically affect the splicing profile of many cancer-associated genes. In addition, the splicing profile of several cancer-associated genes is altered in particular types of cancer arguing for a direct role of specific splicing isoforms in tumor progression. Deciphering the mechanisms underlying aberrant splicing in cancer may prove crucial to understand how splicing machinery is controlled and integrated with other cellular processes, in particular transcription and signaling pathways. Moreover, the characterization of splicing deregulation in cancer will lead to a better comprehension of malignant transformation. Cancer-associated alternative splicing variants may be new tools for the diagnosis and classification of cancers and could be the targets for innovative therapeutical interventions based on highly selective splicing correction approaches.

Sam68 regulates EMT through alternative splicing-activated nonsense-mediated mRNA decay of the SF2/ASF proto-oncogene

Expression levels of SF2/ASF are controlled by Sam68 mediated activation of splicing-induced mRNA decay.

Epithelial-to-mesenchymal transition (EMT) and its reversal (MET) are crucial cell plasticity programs that act during development and tumor metastasis. We have previously shown that the splicing factor and proto-oncogene SF2/ASF impacts EMT/MET through production of a constitutively active splice variant of the Ron proto-oncogene. Using an in vitro model, we now show that SF2/ASF is also regulated during EMT/MET by alternative splicing associated with the nonsense-mediated mRNA decay pathway (AS-NMD). Overexpression and small interfering RNA experiments implicate the splicing regulator Sam68 in AS-NMD of SF2/ASF transcripts and in the choice between EMT/MET programs. Moreover, Sam68 modulation of SF2/ASF splicing appears to be controlled by epithelial cell–derived soluble factors that act through the ERK1/2 signaling pathway to regulate Sam68 phosphorylation. Collectively, our results reveal a hierarchy of splicing factors that integrate splicing decisions into EMT/MET programs in response to extracellular stimuli.

Multilineage hematopoietic reconstitution without clonal selection in ADA-SCID patients treated with stem cell gene therapy

Gene transfer into HSCs is an effective treatment for SCID, although potentially limited by the risk of insertional mutagenesis. We performed a genome-wide analysis of retroviral vector integrations in genetically corrected HSCs and their multilineage progeny before and up to 47 months after transplantation into 5 patients with adenosine deaminase-deficient SCID. Gene-dense regions, promoters, and transcriptionally active genes were preferred retroviral integrations sites (RISs) both in preinfusion transduced CD34(+) cells and in vivo after gene therapy. The occurrence of insertion sites proximal to protooncogenes or genes controlling cell growth and self renewal, including LMO2, was not associated with clonal selection or expansion in vivo. Clonal analysis of long-term repopulating cell progeny in vivo revealed highly polyclonal T cell populations and shared RISs among multiple lineages, demonstrating the engraftment of multipotent HSCs. These data have important implications for the biology of retroviral vectors, the dynamics of genetically modified HSCs, and the safety of gene therapy.

Analysis of ENG and ACVRL1 genes in 137 HHT Italian families identifies 76 different mutations (24 novel). Comparison with other European studies

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder causing vascular dysplasias. About 70-80% of HHT patients carries mutations in ENG or ACVRL1 genes, which code for a TGFbeta receptor type III and I respectively. Molecular data on a large cohort of Italian HHT patients are presented, discussing the significance of missense and splice site mutations. Mutation analysis in ENG and ACVRL1 genes was performed using single strand conformation polymorphisms (SSCP), denaturing high performance liquid chromatography (DHPLC) and subsequent direct sequencing. Overall, 101 mutations were found, with ACVRL1 involved in 71% of cases. The highest number of mutations (28/101 subjects, 14/76 different mutations referring to both genes) was in ACVRL1, exon 3. Mutation analysis was then extended to a total of 356 family members, and 162 proven to carry the mutation. New polymorphisms were identified in both genes, and evidence that ENG P131L change is not a disease-causing mutation was also provided. An in silico analysis was performed in order to characterize splice-site mutations. These results were compared to other European national studies and data from Italy, France and Spain were consistent for an higher incidence of ACVRL1 mutations.

Echocardiographic screening discloses increased values of pulmonary artery systolic pressure in 9 of 68 unselected patients affected with hereditary hemorrhagic telangiectasia

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by the presence of telangiectases and arteriovenous malformations. In some families in whom a form of idiopathic pulmonary arterial hypertension cosegregated with HHT, mutations in the ACVRL1 gene were present.

PURPOSE

We noninvasively measured the pulmonary artery systolic pressure (PASP) in a group of patients with HHT.

METHODS

Doppler transthoracic echocardiography and mutation analysis by direct sequencing were used.

RESULTS

We studied 68 patients (age 19-84 years, mean 50.75 + 15.11; 32 females) and PASP measurement was possible in 44 (64. 7%); in addition, 9 of them (20.5%) showed elevated values. Molecular analysis identified mutations in the ACVRL1 gene in 7 of these 9 subjects. Even on exclusion of relatives of the single case with known pulmonary hypertension, 5 of 37 patients (13.5%) still showed values higher than those of controls.

CONCLUSION

The data indicate that elevated PASP values are a frequent and previously unrecognized complication of HHT. Because clinically significant pulmonary artery hypertension (a relevant cause of morbidity and mortality) may subsequently develop in these patients, we propose that the measurement of PASP should be included among the parameters recorded for all patients undergoing Doppler transthoracic echocardiography during routine clinical screening.