Synergistic inactivation of AXL: a (cross)road to cure ovarian cancer?

The Role of the Tumor Suppressor Gene Protein Tyrosine Phosphatase Gamma in Cancer

Members of the Protein Tyrosine Phosphatase (PTPs) family are associated with growth regulation and cancer development. Acting as natural counterpart of tyrosine kinases (TKs), mainly involved in crucial signaling pathways such as regulation of cell cycle, proliferation, invasion and angiogenesis, they represent key parts of complex physiological homeostatic mechanisms. Protein tyrosine phosphatase gamma (PTPRG) is classified as a R5 of the receptor type (RPTPs) subfamily and is broadly expressed in various isoforms in different tissues. PTPRG is considered a tumor-suppressor gene (TSG) mapped on chromosome 3p14-21, a region frequently subject to loss of heterozygosity in various tumors. However, reported mechanisms of PTPRG downregulation include missense mutations, ncRNA gene regulation and epigenetic silencing by hypermethylation of CpG sites on promoter region causing loss of function of the gene product. Inactive forms or total loss of PTPRG protein have been described in sporadic and Lynch syndrome colorectal cancer, nasopharyngeal carcinoma, ovarian, breast, and lung cancers, gastric cancer or diseases affecting the hematopoietic compartment as Lymphoma and Leukemia. Noteworthy, in Central Nervous System (CNS) PTPRZ/PTPRG appears to be crucial in maintaining glioblastoma cell-related neuronal stemness, carving out a pathological functional role also in this tissue. In this review, we will summarize the current knowledge on the role of PTPRG in various human cancers.

Emerging roles for the GPI-anchored tumor suppressor OPCML in cancers

OPCML is a highly conserved glycosyl phosphatidylinositol (GPI)-anchored protein belonging to the IgLON family of cell adhesion molecules. OPCML functions as a tumor suppressor and is silenced in over 80% of ovarian cancers by loss of heterozygosity and by epigenetic mechanisms. OPCML inactivation is also observed in many other cancers suggesting a conservation of tumor suppressor function. Although epigenetic silencing and subsequent loss of OPCML expression correlate with poor progression-free and overall patient survival, its mechanism of action is only starting to be fully elucidated. Recent discoveries have demonstrated that OPCML exerts its tumor suppressor effect by inhibiting several cancer hallmark phenotypes in vitro and abrogating tumorigenesis in vivo, by downregulating/inactivating a specific spectrum of Receptor Tyrosine Kinases (RTKs), including EphA2, FGFR1, FGFR3, HER2, HER4, and AXL. This modulation of RTKs can also sensitize ovarian and breast cancers to lapatinib, erlotinib, and anti-AXL therapies. Furthermore, OPCML has also been shown to function in synergy with the tumor suppressor phosphatase PTPRG to inactivate pro-metastatic RTKs such as AXL. Recently, the identification of inactivating point mutations and the elucidation of the crystal structure of OPCML have provided valuable insights into its structure-function relationships, giving rise to its potential as an anti-cancer therapeutic.

Nongenetic engineering strategies for regulating receptor oligomerization in living cells

Nongenetic strategies for regulating receptor oligomerization in living cells based on DNA, protein, small molecules and physical stimuli.

Epithelial-to-mesenchymal transition: lessons from development, insights into cancer and the potential of EMT-subtype based therapeutic intervention

Epithelial-to-mesenchymal transition (EMT) is a fundamental developmental process wherein polarized epithelial cells lose their junctional architecture and apical-basal polarity to become motile mesenchymal cells, and there is emerging evidence for its role in propagating tumor dissemination. While many multifaceted nodules converge onto the EMT program, in this review we will highlight the fundamental biology of the signaling schemas that enable EMT. In many cancers, the property of tumor dissemination and metastasis is closely associated with re-enabling developmental properties such as EMT. We discuss the molecular complexity of the tumor heterogeneity in terms of EMT-based gene expression molecular subtypes, and the rewiring of critical signaling nodules in the subtypes displaying higher degrees of EMT can be therapeutically exploited. Specifically in the context of a deadly malignancy such as ovarian cancer where there are no defined mutations or limited biomarkers for developing targeted therapy or personalized medicine, we highlight the importance of identifying EMT-based subtypes that will improve therapeutic intervention. In ovarian cancer, the poor prognosis mesenchymal 'Mes' subtype presents with amplified signaling of the receptor tyrosine kinase (RTK) AXL, extensive crosstalk with other RTKs such as cMET, EGFR and HER2, and sustained temporal activation of extracellular-signal regulated kinase (ERK) leading to induction of EMT transcription factor Slug, underscoring a pathway addiction in Mes that can be therapeutically targeted. We will further examine the emergence of therapeutic modalities in these EMT subtypes and finally conclude with potential interdisciplinary biophysical methodologies to provide additional insights in deciphering the mechanistic and biochemical aspects of EMT. This review intends to provide an overview of the cellular and molecular changes accompanying epithelial-to-mesenchymal transition (EMT) in development and the requisition of this evolutionarily conserved pathway in cancer progression and metastatic disease. Specifically, in a heterogeneous disease such as ovarian cancer lacking defined targetable mutations, the identification of EMT-based subtypes has opened avenues to tailor precision personalized medicine. In particular, using the oncogenic RTK AXL as an example, we will highlight how this classification enables EMT-subtype specific identification of targets that could improve treatment options for patients and how there is a growing need for biophysical approaches to model dynamic processes such as EMT.