Epidermal growth factor-, transforming growth factor-beta-, retinoic acid- and 1,25-dihydroxyvitamin D3-regulated expression of the novel protein PTPIP51 in keratinocytes

MITOL regulates phosphatidic acid-binding activity of RMDN3/PTPIP51

The transfer of phospholipids from the endoplasmic reticulum to mitochondria via the mitochondria-endoplasmic reticulum (ER) contact site (MERCS) is essential for maintaining mitochondrial function and integrity. Here, we identified RMDN3/PTPIP51, possessing phosphatidic acid (PA)-transfer activity, as a neighboring protein of the mitochondrial E3 ubiquitin ligase MITOL/MARCH5 by proximity-dependent biotin labeling using APEX2. We found that MITOL interacts with and ubiquitinates RMDN3. Mutational analysis identified lysine residue 89 in RMDN3 as a site of ubiquitination by MITOL. Loss of MITOL or the substitution of lysine 89 to arginine in RMDN3 significantly reduced the PA-binding activity of RMDN3, suggesting that MITOL regulates the transport of PA to mitochondria by activating RMDN3. Our findings imply that ubiquitin signaling regulates phospholipid transport at the MERCS.

Crosstalks of the PTPIP51 interactome revealed in Her2 amplified breast cancer cells by the novel small molecule LDC3/Dynarrestin

LDC3/Dynarrestin, an aminothiazole derivative, is a recently developed small molecule, which binds protein tyrosine phosphatase interacting protein 51 (PTPIP51). PTPIP51 interacts with various proteins regulating different signaling pathways leading to proliferation and migration. Her2 positive breast cancer cells (SKBR3) express high levels of PTPIP51. Therefore, we investigated the effects of LDC3/Dynarrestin on PTPIP51 and its interactome with 12 different proteins of various signal pathways including the interaction with dynein in SKBR3 cells. The localization and semi-quantification of PTPIP51 protein and the Tyr176 phosphorylated PTPIP51 protein were evaluated. Protein-protein-interactions were assessed by Duolink proximity ligation assays. Interactions and the activation of signal transduction hubs were examined with immunoblots. LDC3/Dynarrestin led to an increased PTPIP51 tyrosine 176 phosphorylation status while the overall amount of PTPIP51 remained unaffected. These findings are paralleled by an enhanced interaction of PTPIP51 with its crucial kinase c-Src and a reduced interaction with the counteracting phosphatase PTP1B. Furthermore, the treatment results in a significantly augmented interaction of PTPIP51/14-3-3β and PTPIP51/Raf1, the link to the MAPK pathway. Under the influence of LDC3/Dynarrestin, the activity of the MAPK pathway rose in a concentration-dependent manner as indicated by RTK assays and immunoblots. The novel small molecule stabilizes the RelA/IκB/PTPIP51 interactome and can abolish the effects caused by TNFα stimulation. Moreover, LDC3/Dynarrestin completely blocked the Akt signaling, which is essential for tumor growth. The data were compared to the recently described interactome of PTPIP51 in LDC3/Dynarrestin treated non-cancerous keratinocyte cells (HaCaT). Differences were identified exclusively for the mitochondrial-associated ER-membranes (MAM) interactions and phospho-regulation related interactome of PTPIP51.LDC3/Dynarrestin gives the opportunity/possibility to influence the MAPK signaling, NFkB signaling and probably calcium homeostasis in breast cancer cells by affecting the PTPIP51 interactome.

Orchestrating cellular signaling pathways-the cellular "conductor" protein tyrosine phosphatase interacting protein 51 (PTPIP51)

The protein tyrosine phosphatase interacting protein 51 (PTPIP51) is thought to regulate crucial cellular functions such as mitosis, apoptosis, migration, differentiation and communication between organelles as a scaffold protein. These diverse functions are modulated by the tyrosine/serine phosphorylation status of PTPIP51. This review interconnects the insights obtained about the action of PTPIP51 in mitogen-activated protein kinase signaling, nuclear factor kB signaling, calcium homeostasis and chromosomal segregation and identifies important signaling hubs. The interference of PTPIP51 in such multiprotein complexes and their PTPIP51-modulated cross-talk makes PTPIP51 an ideal target for novel drugs such as the small molecule LDC-3. Graphical Abstract ᅟ.

PTPIP51—A New RelA-tionship with the NFκB Signaling Pathway

The present study shows a new connection of protein tyrosine phosphatase interacting protein 51 (PTPIP51) to the nuclear factor κB (NFκB) signalling pathway. PTPIP51 mRNA and protein expression is regulated by RelA. If bound to the PTPIP51 promoter, RelA repress the mRNA and protein expression of PTPIP51. The parallel treatment with pyrrolidine dithiocarbamate (PDTC) reversed the suppression of PTPIP51 protein expression induced by TNFα. Using the intensity correlation analysis PTPIP51 verified a co-localization with RelA, which is also regulated by TNFα administration. Moreover, the direct interaction of PTPIP51 and RelA was established using the DuoLink proximity ligation assay. IκBα, the known inhibitor of RelA, also interacted with PTPIP51. This hints to the fact that in un-stimulated conditions PTPIP51 forms a complex with RelA and IκBα. The PTPIP51/RelA/IκBα complex is modulated by TNFα. Interestingly, the impact on the mitogen activated protein kinase pathway was negligible except in highest TNFα concentration. Here, PTPIP51 and Raf-1 interactions were slightly repressed. The newly established relationship of PTPIP51 and the NFκB signaling pathway provides the basis for a possible therapeutic impact.

Emerging drugs for the treatment of diabetic ulcers

INTRODUCTION

Diabetic ulcers are chronic nonhealing ulcerations that despite the available medical tools still result in high amputation rates. Growing evidence suggests that alteration of the biochemical milieu of the chronic wound plays a significant role in impaired diabetic wound healing.

AREAS COVERED

The basic pathophysiology and the conventional treatment strategy of diabetic foot ulcers have been reviewed in the first section. In the second part, the most up-to-date bench and translational research in the field are described. The third section focuses on the drugs currently under development and the ongoing clinical trials evaluating their safety and efficacy. Finally, the major drug development issues and the possible scientific approaches to overcome them are analyzed.

EXPERT OPINION

Significant strides in understanding the chronic wound development have led to the development of topical therapies to address aberrant expression of growth factors and overexpression of inflammatory cytokines. Current research in the laboratory suggests that while decreased growth factor expression occurs at the local wound level, increased systemic serum levels of growth factors suggest growth factor resistance.

Protein tyrosine phosphatase interacting protein 51--a jack-of-all-trades protein

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) interacts both in vitro and in vivo with PTP1B, a protein tyrosine phosphatase involved in cellular regulation. PTPIP51 is known to be expressed in many different types of tissues. It is involved in cellular processes such as proliferation, differentiation and apoptosis. Nevertheless, the exact cellular function of PTPIP51 is still unknown. The present review summarizes our current knowledge of the PTPIP51 gene and its mRNA and protein structure.

Expression profile of PTPIP51 in mouse brain

This study demonstrates the expression of the novel protein protein tyrosine phophatase-interacting protein 51 (PTPIP51) in mammalian brain tissue. Serial sections of the whole adult mouse brain were analyzed for PTPIP51 protein and mRNA by immunohistochemistry, immunoblotting, RT-PCR, and in situ hybridization. Recent investigations by Yu et al. (2008) describe PTPIP51 as being capable of activating Raf-1, thereby modulating the MAPK pathway. The role of Raf-1, as well as of 14-3-3, in neurological disorders is well established. PTPIP51 expression was confined to neurons in the following structures: the piriform cortex and their connections to the anterior commissure, nucleus accumbens, paraventricular and supraoptical nuclei, neurohypophysis, superior colliculus, genu of facialis nerve, spinal trigeminal tract, inferior cerebellar peduncle, and cerebellum. In the cerebellum, a subpopulation of Purkinje cells and their dendrites was strongly PTPIP51 positive. Moreover, PTPIP51 was found to be colocalized with vasopressin and its transport protein neurophysin II in the neuroendocrine nuclei and their connections to the neurohypophysis. The data presented here suggest a role of PTPIP51 in neuronal homeostasis, axonal growth, and transport.

PTPIP51 mRNA and protein expression in tissue microarrays and promoter methylation of benign prostate hyperplasia and prostate carcinoma

BACKGROUND

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) shows a tissue-specific expression pattern and is associated with cellular differentiation and apoptosis in several mammalian tissues. Overexpression of the full-length protein enhances apoptosis. It is also expressed in various carcinomas. In this study the expression of PTPIP51 and its in vitro interaction partners was investigated in human benign prostate hyperplasia (BPH) and in prostate carcinoma (PCa).

METHODS

Tissue microarrays of human BPH and PCa were analyzed by immunohistochemistry. For polymerase chain reaction (PCR), cryo samples of BPH and PCa were used. Bisulfite DNA treatment, followed by sequencing of PCR products was performed in order to analyze CpGs methylation within the promoter region of the PTPIP51 gene.

RESULTS

PTPIP51 mRNA and protein expression was detected in prostatic epithelia of BPH and in tumor cells of PCa, respectively, and within smooth muscle cells of the stromal compartment. A stronger expression was present in nerve fibers, particularly in PCa, in immune cells and in smooth muscle and endothelial cells of vessels of BPH and PCa. On mRNA levels, a slightly elevated expression of PTPIP51 was observed in the PCa group as tested by real-time quantitative PCR analyses. Methylation experiments revealed that at least 70% of methylated CpGs in the CpG island of the PTPIP51 gene promoter region were identified in BPH samples. In contrast, a loss of methylation has been found in the PCa group.

CONCLUSION

The promoter methylation status of PTPIP51 seems to influence the expression of PTPIP51, which was seen as elevated in the PCa.

The novel protein PTPIP51 is expressed in human keratinocyte carcinomas and their surrounding stroma

Background: The novel protein PTPIP51 (SwissProt accession code Q96SD6) is known to interact with two non-transmembrane protein-tyrosine phosphatases, PTP1B and TCPTP in vitro. Overexpression of the full-length protein induces apoptosis in HeLa and HEK293T cells (Lv et al. 2006). PTPIP51 shows a tissue-specific expression pattern and is associated with cellular differentiation and apoptosis in some mammalian tissues, especially in human follicular and interfollicular epidermis. PTPIP51 protein is expressed in all suprabasal layers of normal epidermis, whereas the basal layer contains PTPIP51 mRNA only but lacks the protein. Objectives: The expression of PTPIP51 was investigated in keratinocyte carcinomas, that is human basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) as well as Bowen's disease (BD) and keratoacanthomas (KAs) on a transcriptional (mRNA) and translational (immunohistochemical) level. Methods: Formalin-fixed, paraffin-embedded sections of BCCs, SCCs, KAs and BD, respectively, were analysed by RT-PCR, as well as immunohistochemistry and subsequent fluorescence microscopy. PTPIP51-positive cells of the tumour and the surrounding stroma were identified on the basis of specific morphological features by means of H & E staining. To obtain further information about a putative function of PTPIP51, a possible association of PTPIP51 with apoptotic cells, as well as an assumed negative correlation with proliferating cells was investigated by means of an in-situ TUNEL assay and Ki67/MIB-1 antigen staining, respectively. Co-immunostainings with PTPIP51 were performed for the following antigens: TCPTP, PTP1B and β-catenin. Results: PTPIP51-expression was detected in BCCs and SCCs of the skin, as well as in KAs and BD. Both types of keratinocyte carcinoma revealed a specific localization pattern of PTPIP51 in malignant keratinocytes. Whereas PTPIP51 -positive cells of BCC were found to form two cluster types with a different subcellular localization of the protein, i.e. cytoplasmic and nuclear or predominantly membranous, investigation of SCC revealed a meshwork-like appearance of PTPIP51-positive malignant keratinocytes, created by a mainly membranous localization. BD and KA resembled the findings of PTPIP51-expression in SCC. Furthermore, we observed a partial co-localization of PTP1B and PTPIP51 in BCC. SCC and BCC showed a co-expression and partial co-localization of PTPIP51 with β-catenin. Some PTPIP51-positive cells were found to undergo apoptosis. PTPIP51 was also expressed in cells comprising the surrounding stromal microenvironment. This was particularly noticed for endothelial cells lining peritumoural vessels as well as for infiltrating cells of both, the innate and the adaptive immune system. Conclusions: The results showed a distinct mainly membranous expression pattern of PTPIP51 in BCCs and SCCs. Since PTPIP51 was also detected in the peritumoural tissue, the protein may play a crucial role in keratinocyte tumour development.

Differentiation-dependent PTPIP51 expression in human skeletal muscle cell culture

Protein tyrosine phosphatase-interacting protein 51 (PTPIP51) expression was analyzed in proliferating and differentiating human myogenic cells cultured in vitro. Satellite cell cultures derived from four different individuals were used in this study. To analyze the expression of PTPIP51, myoblasts were cultured under conditions promoting either proliferation or differentiation. In addition, further differentiation of already-differentiated myobtubes was inhibited by resubmitting the cells to conditions promoting proliferation. PTPIP51 protein and mRNA were investigated in samples taken at defined time intervals by immunostaining, immunoblotting, in situ hybridization, and PCR. Image analyses of fluorescence immunostainings were used to quantify PTPIP51 in cultured myoblasts and myotubes. Myoblasts grown in the presence of epidermal and fibroblast growth factors (EGF and FGF), both promoting proliferation, expressed PTPIP51 on a basic level. Differentiation to multinuclear myotubes displayed a linear increase in PTPIP51 expression. The rise in PTPIP51 protein was paralleled by an augmented expression of muscle-specific proteins, namely, sarcoplasmic reticulum Ca(2+) ATPase and myosin heavy-chain protein, both linked to a progressive state of myotubal differentiation. This differentiation-induced increase in PTPIP51 was partly reversible by resubmission of differentiated myotubes to conditions boosting proliferation. The results clearly point toward a strong association between PTPIP51 expression and differentiation in human muscle cells.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers. Although the precise cellular function remains to be elucidated, the current data implicate PTPIP51 in signaling cascades mediating proliferation, differentiation, apoptosis, and motility.

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) mRNA expression and localization and its in vitro interacting partner protein tyrosine phosphatase 1B (PTP1B) in human placenta of the first, second, and third trimester

The cellular localization of protein tyrosine phosphatase 51 (PTPIP51) and its in vitro interacting partner protein tyrosine phosphatase 1B (PTP1B) was studied in human placentae of different gestational stages. The expression of PTPIP51 protein and mRNA was observed in the syncytiotrophoblast and cytotrophoblast layer of placentae from the first, second, and third trimesters. In contrast, PTP1B expression was restricted to the syncytiotrophoblast during all gestational stages. Cells of the cytotrophoblasts and parts of the syncytiotrophoblasts expressing high amounts of PTPIP51 were found to execute apoptosis as shown by TdT-mediated dUTP-biotin nick end labeling assay, cytokeratin 18f, and caspase 3 expression. PTPIP51 could also be traced in the endothelium and smooth muscle cells of placental arterial and venous vessels, identified by double immunostainings with antibodies directed against van Willebrand factor and alpha-smooth muscle actin. Some of these cells showing a high PTPIP51 reactivity were Ki67 positive, indicating proliferation. Additionally, a small population of placental CD14-positive macrophages and mesenchymal cells within the villous stroma were detected as PTPIP51 positive. Our data suggest that both proteins, PTPIP51 and PTP1B, play a role in differentiation and apoptosis of the cytotrophoblast and syncytiotrophoblast, respectively. Moreover, PTPIP51 may also serve as a cellular signaling partner in angiogenesis and vascular remodeling.

Expression of the novel protein PTPIP51 in rat liver: an immunohistochemical study

Expression of the novel protein tyrosine phosphatase interacting protein 51 (PTPIP51) was investigated on mRNA and protein level in the liver of adult Wistar rats. The presence of PTPIP51 mRNA was detected by Northern blotting. Immunostaining showed expression of PTPIP51 protein in distinct non-parenchymal cells. These cells were identified as Kupffer cells, stellate cells and natural killer cells by detection of cell-specific antigens. Whereas most endothelial cells lining large vessels reacted positive to the PTPIP51 antibody, sinusoidal endothelium showed no detectable amount of PTPIP51. Furthermore, PTPIP51 was also found to be expressed in cells forming the biliary tree. An additional subcellular analysis of the non-parenchymal cells by means of electron microscopy showed the presence of PTPIP51 protein in the cytoplasm and in the nuclei of non-parenchymal cells. Most of the hepatocytes did not show any immuno-detectable amount of PTPIP51, yet, some revealed PTPIP51 protein either in the cytoplasm or in the nucleus.