Extracellular matrix degradation via enolase/plasminogen interaction: Evidence for a mechanism conserved in Metazoa.

BACKGROUND INFORMATION: While enolase is a ubiquitous metalloenzyme involved in the glycolytic pathway, it is also known as a multifunctional protein, since enolases anchored on the outer surface of the plasma membrane are involved in tissue invasion. RESULTS: We have identified an extracellular enolase (Ae-ENO) produced by the teratocytes, embryonic cells of the insect parasitoid Aphidius ervi. We demonstrate that Ae-ENO, although lacking a signal peptide, accumulates in cytoplasmic vesicles oriented towards the cell membrane. Ae-ENO binds to and activates a plasminogen-like molecule inducing digestion of the host tissue and thereby ensuring successful parasitism. CONCLUSIONS: These results support the hypothesis that plasminogen-like proteins exist in invertebrates. Interestingly the activation of a plasminogen-like protein is mediated by a mechanisms involving the surface enolase/fibrinolytic system considered, until now, exclusive of vertebrates, and that instead is conserved across species. SIGNIFICANCE: To our knowledge, this is the first example of enolase mediated Plg-like binding and activation in insect cells, demonstrating the existence of an ECM degradation process via a Plg-like protein in invertebrates.

NHE1 promotes invadopodial ECM proteolysis through acidification of the peri-invadopodial space.

Extracellular matrix (ECM) degradation is a critical process in tumor cell invasion and requires membrane and released proteases focalized at membrane structures called invadopodia. While extracellular acidification is important in driving tumor invasion, the structure/function mechanisms underlying this regulation are still unknown. Invadopodia are similar in structure and function to osteoclast podosomes responsible for bone degradation, and extracellular acidification is central to podosome action, suggesting that it could also be for invadopodial function. Here, utilizing a novel system for in situ zymography in native matrices, we show that the Na(+)/H(+) exchanger (NHE1) and NHE1-generated extracellular acidification are localized at and necessary for invadopodial-dependent ECM degradation, thereby promoting tumor invasion. Stimulation with EGF increased both NHE1-dependent proton secretion and ECM degradation. Manipulation of the NHE1 expression by RNA interference or activity via either transport-deficient mutation or the specific inhibitor cariporide confirmed that NHE1 expression and activity are required for invadopodia-mediated ECM degradation. Taken together, our data show a concordance among NHE1 localization, the generation of a well-defined acidic extracellular pH in the nanospace surrounding invadopodia, and matrix-degrading activity at invadopodia of human malignant breast carcinoma cells, providing a structural basis for the role of NHE1 in invasion and identifying NHE1 as a strategic target for therapeutic intervention.

KRAS-regulated glutamine metabolism requires UCP2-mediated aspartate transport to support pancreatic cancer growth.

The oncogenic KRAS mutation has a critical role in the initiation of human pancreatic ductal adenocarcinoma (PDAC) since it rewires glutamine metabolism to increase reduced nicotinamide adenine dinucleotide phosphate (NADPH) production, balancing cellular redox homeostasis with macromolecular synthesis1,2. Mitochondrial glutamine-derived aspartate must be transported into the cytosol to generate metabolic precursors for NADPH production2. The mitochondrial transporter responsible for this aspartate efflux has remained elusive. Here, we show that mitochondrial uncoupling protein 2 (UCP2) catalyses this transport and promotes tumour growth. UCP2-silenced KRASmut cell lines display decreased glutaminolysis, lower NADPH/NADP+ and glutathione/glutathione disulfide ratios and higher reactive oxygen species levels compared to wild-type counterparts. UCP2 silencing reduces glutaminolysis also in KRASWT PDAC cells but does not affect their redox homeostasis or proliferation rates. In vitro and in vivo, UCP2 silencing strongly suppresses KRASmut PDAC cell growth. Collectively, these results demonstrate that UCP2 plays a vital role in PDAC, since its aspartate transport activity connects the mitochondrial and cytosolic reactions necessary for KRASmut rewired glutamine metabolism2, and thus it should be considered a key metabolic target for the treatment of this refractory tumour.

ß1 integrin binding phosphorylates ezrin at T567 to activate a lipid raft signalsome driving invadopodia activity and invasion.

Extracellular matrix (ECM) degradation is a critical process in tumor cell invasion and requires matrix degrading protrusions called invadopodia. The Na(+)/H(+) exchanger (NHE1) has recently been shown to be fundamental in the regulation of invadopodia actin cytoskeleton dynamics and activity. However, the structural link between the invadopodia cytoskeleton and NHE1 is still unknown. A candidate could be ezrin, a linker between the NHE1 and the actin cytoskeleton known to play a pivotal role in invasion and metastasis. However, the mechanistic basis for its role remains unknown. Here, we demonstrate that ezrin phosphorylated at T567 is highly overexpressed in the membrane of human breast tumors and positively associated with invasive growth and HER2 overexpression. Further, in the metastatic cell line, MDA-MB-231, p-ezrin was almost exclusively expressed in invadopodia lipid rafts where it co-localized in a functional complex with NHE1, EGFR, ß1-integrin and phosphorylated-NHERF1. Manipulation by mutation of ezrins T567 phosphorylation state and/or PIP2 binding capacity or of NHE1s binding to ezrin or PIP2 demonstrated that p-ezrin expression and binding to PIP2 are required for invadopodia-mediated ECM degradation and invasion and identified NHE1 as the membrane protein that p-ezrin regulates to induce invadopodia formation and activity.

HPV16 E7-dependent transformation activates NHE1 through a PKA-RhoA-induced inhibition of p38alpha.

BACKGROUND: Neoplastic transformation originates from a large number of different genetic alterations. Despite this genetic variability, a common phenotype to transformed cells is cellular alkalinization. We have previously shown in human keratinocytes and a cell line in which transformation can be turned on and followed by the inducible expression of the E7 oncogene of human papillomavirus type 16 (HPV16), that intracellular alkalinization is an early and essential physiological event driven by the up-regulation of the Na/(+)H(+) exchanger isoform 1 (NHE1) and is necessary for the development of other transformed phenotypes and the in vivo tumor formation in nude mice. METHODOLOGY: Here, we utilize these model systems to elucidate the dynamic sequence of alterations of the upstream signal transduction systems leading to the transformation-dependent activation of NHE1. PRINCIPAL FINDINGS: We observe that a down-regulation of p38 MAPK activity is a fundamental step in the ability of the oncogene to transform the cell. Further, using pharmacological agents and transient transfections with dominant interfering, constitutively active, phosphorylation negative mutants and siRNA strategy to modify specific upstream signal transduction components that link HPV16 E7 oncogenic signals to up-regulation of the NHE1, we demonstrate that the stimulation of NHE1 activity is driven by an early rise in cellular cAMP resulting in the down-stream inhibition of p38 MAPK via the PKA-dependent phosphorylation of the small G-protein, RhoA, and its subsequent inhibition. CONCLUSIONS: All together these data significantly improve our knowledge concerning the basic cellular alterations involved in oncogene-driven neoplastic transformation.