SummaryThe degradation of the extracellular matrix by cancer cells represents an essential step in metastatic progression and this is performed by cancer cell structures called invadopodia. Na V 1.5 (also known as SCN5A) Na + channels are overexpressed in breast cancer tumours and are associated with metastatic occurrence. It has been previously shown that Na V 1.5 activity enhances breast cancer cell invasiveness through perimembrane acidification and subsequent degradation of the extracellular matrix by cysteine cathepsins. Here, we show that Na V 1.5 colocalises with Na + /H + exchanger type 1 (NHE-1) and caveolin-1 at the sites of matrix remodelling in invadopodia of MDA-MB-231 breast cancer cells. NHE-1, Na V 1.5 and caveolin-1 co-immunoprecipitated, which indicates a close association between these proteins. We found that the expression of Na V 1.5 was responsible for the allosteric modulation of NHE-1, rendering it more active at the intracellular pH range of 6.4-7; thus, it potentially extrudes more protons into the extracellular space. Furthermore, Na V 1.5 expression increased Src kinase activity and the phosphorylation (Y421) of the actin-nucleation-promoting factor cortactin, modified F-actin polymerisation and promoted the acquisition of an invasive morphology in these cells. Taken together, our study suggests that Na V 1.5 is a central regulator of invadopodia formation and activity in breast cancer cells.

Previous studies have shown that the PDZ-binding motif of the E6 oncoprotein from the mucosal high-risk (HR) human papillomavirus (HPV) types plays a key role in HPV-mediated cellular transformation in in vitro and in vivo experimental models. HR HPV E6 oncoproteins have the ability to efficiently degrade members of the PDZ motif-containing membrane-associated guanylate kinase (MAGUK) family; however, it is possible that other PDZ proteins are also targeted by E6. Here, we describe a novel interaction of HPV type 16 (HPV16) E6 with a PDZ protein, Na ؉ /H ؉ exchange regulatory factor 1 (NHERF-1), which is involved in a number of cellular processes, including signaling and transformation. HPV16 E6 associates with and promotes the degradation of NHERF-1, and this property is dependent on the C-terminal PDZ-binding motif of E6. Interestingly, HPV16 E7, via the activation of the cyclin-dependent kinase complexes, promoted the accumulation of a phosphorylated form of NHERF-1, which is preferentially targeted by E6. Thus, both oncoproteins appear to cooperate in targeting NHERF-1. Notably, HPV18 E6 is not able to induce NHERF-1 degradation, indicating that this property is not shared with E6 from all HR HPV types. Downregulation of NHERF-1 protein levels was also observed in HPV16-positive cervical cancer-derived cell lines, such as SiHa and CaSki, as well as HPV16-positive cervical intraepithelial neoplasia (CIN). Finally, our data show that HPV16-mediated NHERF-1 degradation correlates with the activation of the phosphatidylinositol-3-OH kinase (PI3K)/AKT signaling pathway, which is known to play a key role in carcinogenesis.Approximately 15 mucosal human papillomavirus (HPV) types, referred to as high-risk (HR) HPV types, are linked to the development of cervical cancer and a subset of other anogenital cancers (28). HPV type 16 (HPV16) is the most common type within the HR HPV group, being responsible for approximately 50% of all cervical cancers worldwide (12). Biological studies have demonstrated that E6 and E7 play a key role in HPV-mediated carcinogenesis (5). Both viral oncoproteins display transforming properties in in vitro and in vivo experimental models, mainly by interacting with and neutralizing the functions of several cellular proteins, including products of tumor suppressor genes (5). E7 from HPV16 and other HR HPV types deregulates cell cycle control by targeting the retinoblastoma tumor suppressor protein (pRb1) and its related proteins p107 and p130, also termed pocket proteins (5). pRb1 negatively regulates, via direct association, the activity of several transcription factors, including members of the E2F family. HPV16 E7 is able to directly interact with pRb1, promoting its degradation via the proteasome pathway. This event results in the release and constitutive activation of E2F complexes that, in turn, initiate the transcription of genes encoding positive cell cycle regulators, such as cyclin E and cyclin A.Like E7, the HR HPV E6 oncoprotein associates with another tumor suppressor, p53, leadi...

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.

Degradation of the extracellular matrix (ECM) is a critical step of tumor cell invasion and requires protease-dependent proteolysis focalized at the invadopodia where the proteolysis of the ECM occurs. Most of the extracellular proteases belong to serine- or metallo-proteases and the invadopodia is where protease activity is regulated. While recent data looking at global protease activity in the growth medium reported that their activity and role in invasion is dependent on Na+/H+ exchanger 1 (NHE1)-driven extracellular acidification, there is no data on this aspect at the invadopodia, and an open question remains whether this acid extracellular pH (pHe) activation of proteases in tumor cells occurs preferentially at invadopodia. We previously reported that the NHE1 is expressed in breast cancer invadopodia and that the NHE1‑dependent acidification of the peri-invadopodial space is critical for ECM proteolysis. In the present study, using, for the first time, in situ zymography analysis, we demonstrated a concordance between NHE1 activity, extracellular acidification and protease activity at invadopodia to finely regulate ECM digestion. We demonstrated that: (i) ECM proteolysis taking place at invadopodia is driven by acidification of the peri-invadopodia microenvironment; (ii) that the proteases have a functional pHe optimum that is acidic; (iii) more than one protease is functioning to digest the ECM at these invadopodial sites of ECM proteolysis; and (iv) lowering pHe or inhibiting the NHE1 increases protease secretion while blocking protease activity changes NHE1 expression at the invadopodia.