In cancer, the deregulation of growth signaling pathways drives changes in the cell's architecture and its environment that allow autonomous growth of tumors. These cells then acquire a tumor-initiating "stemness" phenotype responsible for disease advancement to more aggressive stages. Here, we show that high levels of the actin cytoskeleton-associated protein WIP (WASP-interacting protein) correlates with tumor growth, both of which are linked to the tumor-initiating cell phenotype. We find that WIP controls tumor growth by boosting signals that stabilize the YAP/TAZ complex via a mechanism mediated by the endocytic/endosomal system. When WIP levels are high, the β-catenin Adenomatous polyposis coli (APC)-axin-GSK3 destruction complex is sequestered to the multi-vesicular body compartment, where its capacity to degrade YAP/TAZ is inhibited. YAP/TAZ stability is dependent on Rac, p21-activated kinase (PAK) and mammalian diaphanous-related formin (mDia), and is Hippo independent. This close biochemical relationship indicates an oncogenic role for WIP in the physiology of cancer pathology by increasing YAP/TAZ stability.

The cancer stem cell (CSC) hypothesis suggests that tumours are maintained by a subpopulation of cells with stem cell properties. Although the existence of CSCs was initially described in human leukaemia, less evidence exists for CSCs in solid tumours. Recently, a CD133+ cell subpopulation was isolated from human brain tumours exhibiting stem cell properties in vitro as well as the capacity to initiate tumours in vivo. In the present work, we try to summarize the data showing that some elements of the Phosphoinositide 3-kinase Class I (PI3K)/ Thymoma viral oncogene protein kinase (Akt) pathway, such the activity of PI3K Class I or Akt2, are necessary to maintain the CSC-like phenotype as well as survival of CSCs (also denoted as tumour-initiating cells (TICs)). Our data and other laboratory data permit a working hypothesis in which each Akt isoform plays an important and specific role in CSC/TIC growth, self-renewal, maintaining survival, and epithelial-mesenchymal transition (EMT) phenotype, not only in breast cancer, but also in glioma. We suggest that a more complete understanding is needed of the possible roles of isoforms in human tumours (iso-signalling determination). Thus, a comprehensive analysis of how hierarchical signalling is assembled during oncogenesis, how cancer landmarks are interconnected to favour CSC and tumour growth, and how some protein isoforms play a specific role in CSCs to ensure that survival and proliferation must be done in order to propose/generate new therapeutic approaches (alone or in combination with existing ones) to use against cancer.

Cancer cells form actin-rich degradative protrusions (invasive pseudopods and invadopodia), which allows their efficient dispersal during metastasis. Using biochemical and advanced imaging approaches, we demonstrate that the N-WASP-interactors WIP and WICH/WIRE play non-redundant roles in cancer cell invasion. WIP interacts with N-WASP and cortactin and is essential for invadopodium assembly, whereas WICH/WIRE regulates N-WASP activation to control invadopodium maturation and degradative activity. Our data also show that Nck interaction with WIP and WICH/WIRE modulates invadopodium maturation; changes in WIP and WICH/WIRE levels induce differential distribution of Nck. We show that WIP can replace WICH/WIRE functions and that elevated WIP levels correlate with high invasiveness. These findings identify a role for WICH/WIRE in invasiveness and highlight WIP as a hub for signaling molecule recruitment during invadopodium generation and cancer progression, as well as a potential diagnostic biomarker and an optimal target for therapeutic approaches.

The spatial distribution of signals downstream from receptor tyrosine kinases (RTKs) or G-protein coupled receptors (GPCR) regulates fundamental cellular processes that control cell migration and growth. Both pathways rely significantly on actin cytoskeleton reorganization mediated by nucleation-promoting factors such as the WASP-(Wiskott-Aldrich Syndrome Protein) family. WIP (WASP Interacting Protein) is essential for the formation of a class of polarised actin microdomain, namely dorsal ruffles, downstream of the RTK for PDGF (platelet-derived growth factor) but the underlying mechanism is poorly understood. Using lentivirally-reconstituted WIP-deficient murine fibroblasts we define the requirement for WIP interaction with N-WASP (neural WASP) and Nck for efficient dorsal ruffle formation and of WIP-Nck binding for fibroblast chemotaxis towards PDGF-AA. The formation of both circular dorsal ruffles in PDGF-AA-stimulated primary fibroblasts and lamellipodia in CXCL13-treated B lymphocytes are also compromised by WIP-deficiency. We provide data to show that a WIP-Nck signalling complex interacts with RTK to promote polarised actin remodelling in fibroblasts and provide the first evidence for WIP involvement in the control of migratory persistence in both mesenchymal (fibroblast) and amoeboid (B lymphocytes) motility.

Wild-type p53 (wtp53) is described as a tumour suppressor gene, and mutations in p53 occur in many human cancers. Indeed, in high-grade malignant glioma, numerous molecular genetics studies have established central roles of RTK-PI3K-PTEN and ARF-MDM2-p53 INK4a-RB pathways in promoting oncogenic capacity. Deregulation of these signalling pathways, among others, drives changes in the glial/stem cell state and environment that permit autonomous growth. The initially transformed cell may undergo subsequent modifications, acquiring a more complete tumour-initiating phenotype responsible for disease advancement to stages that are more aggressive. We recently established that the oncogenic activity of mutant p53 (mtp53) is driven by the actin cytoskeleton-associated protein WIP (WASP-interacting protein), correlated with tumour growth, and more importantly that both proteins are responsible for the tumour-initiating cell phenotype. We reported that WIP knockdown in mtp53-expressing glioblastoma greatly reduced proliferation and growth capacity of cancer stem cell (CSC)-like cells and decreased CSC-like markers, such as hyaluronic acid receptor (CD44), prominin-1 (CD133), yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ). We thus propose a new CSC signalling pathway downstream of mtp53 in which Akt regulates WIP and controls YAP/TAZ stability. WIP drives a mechanism that stimulates growth signals, promoting YAP/TAZ and β-catenin stability in a Hippo-independent fashion, which allows cells to coordinate processes such as proliferation, stemness and invasiveness, which are key factors in cancer progression. Based on this multistep tumourigenic model, it is tantalizing to propose that WIP inhibitors may be applied as an effective anti-cancer therapy.