PTPN14 is required for the density-dependent control of YAP1

The expanding family of FERM proteins

Our understanding of the FERM (4.1/ezrin/radixin/moesin) protein family has been rapidly expanding in the last few years, with the result that many new physiological functions have been ascribed to these biochemically unique proteins. In the present review, we will discuss a number of new FRMD (FERM domain)-containing proteins that were initially discovered from genome sequencing but are now being established through biochemical and genetic studies to be involved both in normal cellular processes, but are also associated with a variety of human diseases.

What do mechanotransduction, Hippo, Wnt, and TGFβ have in common? YAP and TAZ as key orchestrating molecules in ocular health and disease

Cells in vivo are exposed to a complex signaling environment. Biochemical signaling modalities, such as secreted proteins, specific extracellular matrix domains and ion fluxes certainly compose an important set of regulatory signals to cells. However, these signals are not exerted in isolation, but rather in concert with biophysical cues of the surrounding tissue, such as stiffness and topography. In this review, we attempt to highlight the biophysical attributes of ocular tissues and their influence on cellular behavior. Additionally, we introduce the proteins YAP and TAZ as targets of biophysical and biochemical signaling and important agonists and antagonists of numerous signaling pathways, including TGFβ and Wnt. We frame the discussion around this extensive signaling crosstalk, which allows YAP and TAZ to act as orchestrating molecules, capable of integrating biophysical and biochemical cues into a broad cellular response. Finally, while we draw on research from various fields to provide a full picture of YAP and TAZ, we attempt to highlight the intersections with vision science and the exciting work that has already been performed.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Drosophila ste-20 family protein kinase, hippo, modulates fat cell proliferation

Background

Evolutionarily conserved Hippo (Hpo) pathway plays a pivotal role in the control of organ size. Although the Hpo pathway regulates proliferation of a variety of epidermal cells, its function in non-ectoderm-derived cells is largely unknown.

Methodology/Principal Findings

Through methods including fat quantification assays, starvation assays, in vivo labeling assays, we show that overexpression of Hpo in Drosophila melanogaster fat body restricts Drosophila body growth and reduces fat storage through regulation of adipocyte proliferation rather than through influencing the size of fat cells and lipid metabolism, whereas compromising Hpo activity results in weight gain and greater fat storage. Furthermore, we provide evidence that Yorkie (Yki, a transcriptional coactivator that functions in the Hpo pathway) antagonizes Hpo to modulate fat storage in Drosophila.

Conclusions/Significance

Our findings specify a role of Hpo in controlling mesoderm-derived cell proliferation. The observed anti-obesity effects of Hpo may indicate great potential for its utilization in anti-obesity therapeutics.

The tyrosine phosphatase PTPN14 is a negative regulator of YAP activity

The Hippo (Hpo) pathway is a novel signaling pathway that controls organ size in Drosophila and mammals and is deregulated in a variety of human cancers. It consists of a set of kinases that, through a number of phosphorylation events, inactivate YAP, a transcriptional co-activator that controls cellular proliferation and apoptosis. We have identified PTPN14 as a YAP-binding protein that negatively regulates YAP activity by controlling its localization. Mechanistically, we find that the interaction of ectopic YAP with PTPN14 can be mediated by the respective WW and PPxY motifs. However, the PTPN14 PPxY motif and phosphatase activity appear to be dispensable for the negative regulation of endogenous YAP, likely suggesting more complex mechanisms of interaction and modulation. Finally, we demonstrate that PTPN14 downregulation can phenocopy YAP activation in mammary epithelial cells and synergize with YAP to induce oncogenic transformation.

The Hippo pathway: regulators and regulations

Control of cell number is crucial in animal development and tissue homeostasis, and its dysregulation may result in tumor formation or organ degeneration. The Hippo pathway in both Drosophila and mammals regulates cell number by modulating cell proliferation, cell death, and cell differentiation. Recently, numerous upstream components involved in the Hippo pathway have been identified, such as cell polarity, mechanotransduction, and G-protein-coupled receptor (GPCR) signaling. Actin cytoskeleton or cellular tension appears to be the master mediator that integrates and transmits upstream signals to the core Hippo signaling cascade. Here, we review regulatory mechanisms of the Hippo pathway and discuss potential implications involved in different physiological and pathological conditions.

The Hippo size control pathway--ever expanding

An important regulator of organ size and tumorigenesis is the Hippo pathway. Recent studies have unveiled increasing complexity in regulation of Hippo pathway activity at the level of the oncoprotein Yes-associated protein (YAP). The protein tyrosine phosphatase 14 (PTPN14, known as Pez in Drosophila) was identified as a protein that antagonizes the function of the key Hippo pathway protein YAP by promoting its cytoplasmic localization under high cell density conditions. In Drosophila, Pez was identified as a repressor of epithelial proliferation in vivo. Studies in mammalian cells showed that a family of G protein-coupled receptors, the protease-activated receptors, functioned as activators of YAP. These studies shed light on the intricate regulation of the Hippo pathway and also highlight the importance of investigating these newly discovered regulatory links in physiological and pathological settings to fully appreciate their importance.

Proteomic approaches to the study of papillomavirus-host interactions

The identification of interactions between viral and host cellular proteins has provided major insights into papillomavirus research, and these interactions are especially relevant to the role of papillomaviruses in the cancers with which they are associated. Recent advances in mass spectrometry technology and data processing now allow the systematic identification of such interactions. This has led to an improved understanding of the different pathologies associated with the many papillomavirus types, and the diverse nature of these viruses is reflected in the spectrum of interactions with host proteins. Here we review a history of proteomic approaches, particularly as applied to the papillomaviruses, and summarize current techniques. Current proteomic studies on the papillomaviruses use yeast-two-hybrid or affinity purification-mass spectrometry approaches. We detail the advantages and disadvantages of each and describe current examples of papillomavirus proteomic studies, with a particular focus on the HPV E6 and E7 oncoproteins.