Comparative analysis of the Band 4.1/ezrin-related protein tyrosine phosphatase Pez from two Drosophila species: implications for structure and function

Cell Junctions in Hippo Signaling

The Hippo signal transduction pathway is an important regulator of organ growth and cell differentiation, and its deregulation contributes to the development of cancer. The activity of the Hippo pathway is strongly dependent on cell junctions, cellular architecture, and the mechanical properties of the microenvironment. In this review, we discuss recent advances in our understanding of how cell junctions transduce signals from the microenvironment and control the activity of the Hippo pathway. We also discuss how these mechanisms may control organ growth during development and regeneration, and how defects in them deregulate Hippo signaling in cancer cells.

A Drosophila-centric view of protein tyrosine phosphatases

Most of our knowledge on protein tyrosine phosphatases (PTPs) is derived from human pathologies and mouse knockout models. These models largely correlate well with human disease phenotypes, but can be ambiguous due to compensatory mechanisms introduced by paralogous genes. Here we present the analysis of the PTP complement of the fruit fly and the complementary view that PTP studies in Drosophila will accelerate our understanding of PTPs in physiological and pathological conditions. With only 44 PTP genes, Drosophila represents a streamlined version of the human complement. Our integrated analysis places the Drosophila PTPs into evolutionary and functional contexts, thereby providing a platform for the exploitation of the fly for PTP research and the transfer of knowledge onto other model systems.

Drosophila Pez acts in Hippo signaling to restrict intestinal stem cell proliferation

The conserved Hippo signaling pathway acts in growth control and is fundamental to animal development and oncogenesis. Hippo signaling has also been implicated in adult midgut homeostasis in Drosophila. Regulated divisions of intestinal stem cells (ISCs), giving rise to an ISC and an enteroblast (EB) that differentiates into an enterocyte (EC) or an enteroendocrine (EE) cell, enable rapid tissue turnover in response to intestinal stress. The damage-related increase in ISC proliferation requires deactivation of the Hippo pathway and consequential activation of the transcriptional coactivator Yorkie (Yki) in both ECs and ISCs. Here, we identify Pez, an evolutionarily conserved FERM domain protein containing a protein tyrosine phosphatase (PTP) domain, as a novel binding partner of the upstream Hippo signaling component Kibra. Pez function--but not its PTP domain--is essential for Hippo pathway activity specifically in the fly midgut epithelium. Thus, Pez displays a tissue-specific requirement and functions as a negative upstream regulator of Yki in the regulation of ISC proliferation.

Protein tyrosine phosphatase non-receptor type 14 is a novel sperm-motility biomarker

PURPOSE

To understand the molecular basis of sperm-motility and to identify related novel motility biomarkers.

METHODS

Two-dimensional electrophoresis (2DE) followed by Reverse-phase-nano-high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (RP-nano-HPLC-ESI-MS/MS) were applied to establish the human sperm proteome. Then the sperm proteome of moderate-motile human sperm fraction and that of good-motile human sperm fraction from pooled spermatozoa of forty normozoospermic donors (Group 1 subjects) were compared to identify the dysregulated proteins. Among these down-regulated proteins, Protein tyrosine phosphatase non-receptor type 14 (PTPN14) was chosen to reconfirm by Western blotting and semi-quantitative reverse transcription polymerase chain reaction. For clinical application, Western blotting and real-time reverse transcription polymerase chain reaction was performed to compare the expression level of PTPN14 in (Group 2 subjects) nine normozoospermic controls and thirty-three asthenozoospermic patients (including 21 mild asthenozoospermic cases and 12 severe cases). Finally, bioinformatic tools prediction and immunofluorescence assay were performed to elucidate the potential localization of PTPN14.

RESULTS

The expression levels of three proteins were observed to be lower in the moderate-motile sperm fraction than in good-motile sperm of group 1 subjects. Among three proteins with persistent down-regulation in the moderate-motile sperm, we reconfirmed that the expression level of PTPN14 was significantly lower in both mRNA and protein levels from the moderate-motile sperm fraction. Further, down-regulation of PTPN14 was found at the translational and transcriptional level in the asthenozoospermic men. Finally, Bioinformatic tools prediction and immunofluorescence assay showed that PTPN14 maybe predominantly localized at the mitochondria in the midpiece of human ejaculated sperm.

CONCLUSIONS

Proteomics tools were applied to identify three possible sperm motility-related proteins. Among these proteins, PTPN14 was highly likely a novel sperm-motility biomarker and a potential mitochondrial protein.

ERM proteins and merlin: integrators at the cell cortex

A fundamental property of many plasma-membrane proteins is their association with the underlying cytoskeleton to determine cell shape, and to participate in adhesion, motility and other plasma-membrane processes, including endocytosis and exocytosis. The ezrin-radixin-moesin (ERM) proteins are crucial components that provide a regulated linkage between membrane proteins and the cortical cytoskeleton, and also participate in signal-transduction pathways. The closely related tumour suppressor merlin shares many properties with ERM proteins, yet also provides a distinct and essential function.