Trefoil factor family peptide 2 acts pro-proliferative and pro-apoptotic in the murine retina

Plasma Biomarkers of Reticular Pseudodrusen and the Risk of Progression to Advanced Age-Related Macular Degeneration

Purpose

To determine, using an aptamer-based technology in patients with intermediate age-related macular degeneration (AMD), (1) if there is a difference in plasma levels of 4979 proteins in patients with and without reticular pseudodrusen (RPD), and (2) if plasma levels of proteins are related to time to conversion to advanced AMD.

Methods

Patients with intermediate AMD and RPD were identified from an AMD registry. Relative concentrations of each protein were log (base 2) transformed and compared between patients with and without RPD using linear regression. A Cox proportional hazards survival model was fit to each aptamer to quantify associations with time to conversion. A pathway analysis was conducted in converters versus non-converters using the Reactome database.

Results

Of the 109 intermediate AMD patients, 39 had bilateral RPD (36%). Two proteins, TCL1A and CNDP1, were lower in patients in the intermediate AMD group with RPD. Twenty-one patients converted to advanced AMD with a median time to conversion of 25.2 months (range, 2.3-48.5 months) and median follow-up time in non-converters of 26.4 months (range, 0.03-49.7 months). Several proteins (lysozyme C, TFF3, RNAS6, and SAP3) distinguished patients who converted from those who did not convert to advanced AMD. The top conversion pathways included tumor necrosis factors bind their physiological receptors, digestion and absorption, signaling by activin, and signaling by TGF-β family members.

Conclusions

We identified a protein signature related to RPD, as well as to conversion to advanced AMD. The pathway analysis suggests that dysfunction of critical systemic pathways may have links to conversion to advanced AMD.

Translational Relevance

Biomarkers identified in plasma likely reflect systemic alterations in protein expression in patients with intermediate AMD.

Localization of trefoil factor family peptide 3 (TFF3) in epithelial tissues originating from the three germ layers of developing mouse embryo

Trefoil factor family (TFF) peptides are involved in the maintenance of epithelial integrity and epithelial restitution. Mature epithelial tissues originate from different embryonic germ layers. The objective of this research was to explore the presence and localization of TFF3 peptide in mouse embryonic epithelia and to examine if the occurrence of TFF3 peptide is germ layer-dependent. Mouse embryos (14-18 days old) were fixed in 4% paraformaldehyde and embedded in paraffin. Immunohistochemistry was performed with affinity purified rabbit anti-TFF3 antibody, goat anti-rabbit biotinylated secondary antibody and streptavidin-horseradish peroxidase, followed by 3,3'-diaminobenzidine. TFF3 peptide was present in the gastric and intestinal mucosa, respiratory mucosa in the upper and lower airways, pancreas, kidney tubules, epidermis, and oral cavity. The presence and localization of TFF3 peptide was associated with the embryonic stage and tissue differentiation. TFF3 peptide distribution specific to the germ layers was not observed. The role of TFF3 peptide in cell migration and differentiation, immune response, and apoptosis might be associated with specific embryonic epithelial cells. TFF3 peptide may also be considered as a marker for mucosal maturation.

Forced Trefoil Factor Family Peptide 3 (TFF3) Expression Reduces Growth, Viability, and Tumorigenicity of Human Retinoblastoma Cell Lines

Trefoil factor family (TFF) peptides have been shown to effect cell proliferation, apoptosis, migration and invasion of normal cells and various cancer cell lines. In the literature TFF peptides are controversially discussed as tumor suppressors and potential tumor progression factors. In the study presented, we investigated the effect of TFF3 overexpression on growth, viability, migration and tumorigenicity of the human retinoblastoma cell lines Y-79, WERI-Rb1, RBL-13 and RBL-15. As revealed by WST-1 and TUNEL assays as well as DAPI and BrdU cell counts, recombinant human TFF3 significantly lowers retinoblastoma cell viability and increases apoptosis levels. Transient TFF3 overexpression likewise significantly increases RB cell apoptosis. Stable, lentiviral TFF3 overexpression lowers retinoblastoma cell viability, proliferation and growth and significantly increases cell death in retinoblastoma cells. Blockage experiments using a broad-spectrum caspase inhibitor and capase-3 immunocytochemistry revealed the involvement of caspases in general and of caspase-3 in particular in TFF3 induced apoptosis in retinoblastoma cell lines. Soft agarose and in ovo chicken chorioallantoic membrane (CAM) assays revealed that TFF3 overexpression influences anchorage independent growth and significantly decreases the size of tumors forming from retinoblastoma cells. Our study demonstrates that forced TFF3 expression exerts a significant pro-apoptotic, anti-proliferative, and tumor suppressive effect in retinoblastoma cells, setting a starting point for new additive chemotherapeutic approaches in the treatment of retinoblastoma.

Trefoil factor family peptides – friends or foes?

Trefoil factor family (TFF) peptides are a group of molecules bearing a characteristic three-loop trefoil domain. They are mainly secreted in mucous epithelia together with mucins but are also synthesized in the nervous system. For many years, TFF peptides were only known for their wound healing and protective function, e.g. in epithelial protection and restitution. However, experimental evidence has emerged supporting a pivotal role of TFF peptides in oncogenic transformation, tumorigenesis and metastasis. Deregulated expression of TFF peptides at the gene and protein level is obviously implicated in numerous cancers, and opposing functions as oncogenes and tumor suppressors have been described. With regard to the regulation of TFF expression, epigenetic mechanisms as well as the involvement of various miRNAs are new, promising aspects in the field of cancer research. This review will summarize current knowledge about the expression and regulation of TFF peptides and the involvement of TFF peptides in tumor biology and cancerogenesis.

Trefoil factor family peptides TFF1 and TFF3 in the nervous tissues of developing mouse embryo

Trefoil factor family peptides (TFF1, TFF2, and TFF3) are predominantly found in mucous epithelia of various organs. However, they have also been reported in the nervous tissue, particularly mouse, rat, porcine, and human brain. The aim of this research was to determine the presence of TFF1 and TFF3 in the nervous system of developing mouse embryo. Mouse embryos, at the stages E15 to E17 were isolated, fixed in 4% paraformaldehyde and embedded in paraffin blocks. Sagittal 6µm sections were made, processed for immunohistochemistry, and incubated with anti-TFF1 or anti-TFF3 primary polyclonal rabbit antibodies. Labeled streptavidin-biotin method was used for TFF detection. TFF1 and 3 were found in the cytoplasm of ganglion cell somata, while TFF3 staining was also visible in the cytoplasm of neurons in different areas and nuclei of brain and medulla oblongata. Neurons in the gray matter of spinal cord were also TFF1 and TFF3 positive, and signal for both peptides was found in the choroid plexus. TFF peptides might be involved in the complex processes of nervous system development and differentiation and brain plasticity.

CALIBRATING NON-CONVEX PENALIZED REGRESSION IN ULTRA-HIGH DIMENSION

We investigate high-dimensional non-convex penalized regression, where the number of covariates may grow at an exponential rate. Although recent asymptotic theory established that there exists a local minimum possessing the oracle property under general conditions, it is still largely an open problem how to identify the oracle estimator among potentially multiple local minima. There are two main obstacles: (1) due to the presence of multiple minima, the solution path is nonunique and is not guaranteed to contain the oracle estimator; (2) even if a solution path is known to contain the oracle estimator, the optimal tuning parameter depends on many unknown factors and is hard to estimate. To address these two challenging issues, we first prove that an easy-to-calculate calibrated CCCP algorithm produces a consistent solution path which contains the oracle estimator with probability approaching one. Furthermore, we propose a high-dimensional BIC criterion and show that it can be applied to the solution path to select the optimal tuning parameter which asymptotically identifies the oracle estimator. The theory for a general class of non-convex penalties in the ultra-high dimensional setup is established when the random errors follow the sub-Gaussian distribution. Monte Carlo studies confirm that the calibrated CCCP algorithm combined with the proposed high-dimensional BIC has desirable performance in identifying the underlying sparsity pattern for high-dimensional data analysis.

Trefoil factor 2 promotes cell proliferation in pancreatic β-cells through CXCR-4-mediated ERK1/2 phosphorylation

Decreased β-cell mass is a hallmark of type 2 diabetes, and therapeutic approaches to increase the pancreatic β-cell mass have been expected. In recent years, gastrointestinal incretin peptides have been shown to exert a cell-proliferative effect in pancreatic β-cells. Trefoil factor 2 (TFF2), which is predominantly expressed in the surface epithelium of the stomach, plays a role in antiapoptosis, migration, and proliferation. The TFF family is expressed in pancreatic β-cells, whereas the role of TFF2 in pancreatic β-cells has been obscure. In this study, we investigated the mechanism by which TFF2 enhances pancreatic β-cell proliferation. The effects of TFF2 on cell proliferation were evaluated in INS-1 cells, MIN6 cells, and mouse islets using an adenovirus vector containing TFF2 or a recombinant TFF2 peptide. The forced expression of TFF2 led to an increase in bromodeoxyuridine (BrdU) incorporation in both INS-1 cells and islets, without any alteration in insulin secretion. TFF2 significantly increased the mRNA expression of cyclin A2, D1, D2, D3, and E1 in islets. TFF2 peptide increased ERK1/2 phosphorylation and BrdU incorporation in MIN6 cells. A MAPK kinase inhibitor (U0126) abrogated the TFF2 peptide-mediated proliferation of MIN6 cells. A CX-chemokine receptor-4 antagonist also prevented the TFF2 peptide-mediated increase in ERK1/2 phosphorylation and BrdU incorporation in MIN6 cells. These results indicated that TFF2 is involved in β-cell proliferation at least partially via CX-chemokine receptor-4-mediated ERK1/2 phosphorylation, suggesting TFF2 may be a novel target for inducing β-cell proliferation.

Human gastric TFF2 peptide contains an N-linked fucosylated N,N'-diacetyllactosediamine (LacdiNAc) oligosaccharide

In the human stomach, the peptide trefoil factor family 2 (TFF2) is secreted together with the mucin MUC6 by mucous neck cells (MNCs) and antral gland cells. TFF2 is strongly associated with the gastric mucus and promotes gastric restitution. Here, TFF2 was purified from the human corpus and antrum, respectively, by size-exclusion chromatography, and the N-linked glycan structure at N-15 of the mature peptide was determined. As a hallmark, the unusual monofucosylated N,N'-diacetylhexosediamine (tentatively assigned as GalNAcβ1 → 4GlcNAc, LacdiNAc) modification was detected as the terminal structure of a bi-antennary complex type N-glycan exhibiting also core fucosylation. Replicate analyses did not show microheterogeneities in the fraction of peptide-N-glycosidase F cleaved and permethylated N-glycans when analyzed by matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS). On the glycopeptide level, a minor glycan microheterogeneity was evident in liquid chromatography-electrospray ionization (ESI)-MS, demonstrating the presence of underfucosylated species. The tryptic TFF2 N-glycopeptide p34-39 (LSPHNR N-glycosylated with Fuc3Hex3HexNAc6) was identified by both ESI-tandem mass spectrometry and MALDI-post-source decay analysis. Lectin analyses with the Wisteria floribunda agglutinin indicated the potential presence of LacdiNAc terminating glycans and revealed minor differences between TFF2 from fundic units, i.e. MNCs, and antral units, i.e. antral gland cells. Strikingly, on the level of the primary structure, there was no indication that the formation of the proposed LacdiNAc structure is cis-controlled by a peptidic determinant related to the published sequences.

High trefoil factor 1 (TFF1) expression in human retinoblastoma cells correlates with low growth kinetics, increased cyclin-dependent kinase (CDK) inhibitor levels and a selective down-regulation of CDK6

Trefoil factor family (TFFs) peptides facilitate epithelial restitution, but also effect cell proliferation and apoptosis of normal and various cancer cell lines. In a recent study by our group, TFF2 expression was demonstrated in the murine retina, where it exhibits pro-proliferative and pro-apoptotic effects. In the present study, we investigated the expression and function of TFF peptides in eight human retinoblastoma cell lines. TFF1 was the only TFF peptide expressed at detectable levels in immunoblots of retinoblastoma cells. TFF1 expression levels were highly variable in different retinoblastoma cell lines and negatively correlated with cell growth curves. Recombinant human TFF1 had a negative effect on cell viability and caused a reduction in cell proliferation. Retinoblastoma cell lines with high TFF1 expression levels exhibited a selective down-regulation of cyclin-dependent kinase (CDK) 6, whereas CDK4 and CDK2 seem to be unaffected by TFF1 expression. In immunocytochemical studies, we observed a nuclear co-localization of TFF1 and CDK2 in Cajal bodies (CBs). In high TFF1 expressing human retinoblastoma cell lines CBs were smaller and higher in number compared to retinoblastoma lines with low TFF1 expression, indicating differences in cell cycle status between the different retinoblastoma cell lines. Our data further support the notion for a potential tumor suppressor function of TFF1. The nuclear localization of TFF1 in CBs--considered to play a role in cell cycle progression, potentially acting as a platform for CDK-cyclin function-offers a new impetus in the ongoing search for potential TFF1 interacting proteins.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.