HOPX: A Unique Homeodomain Protein in Development and Tumor Suppression

Simple Summary

Homeobox (HOX) genes encode homeodomain proteins that regulate a wide range of molecular pathways. The homeodomain is highly conserved and binds to DNA. One exception is homeodomain-only protein (HOPX) that lacks DNA-binding capacity. HOPX plays a crucial role in development and its functional impairment is associated with a variety of diseases, including cancer. Loss of HOPX function occurs in a wide range of cancer types, where it functions as a tumor suppressor gene. Understanding the molecular mechanisms by which HOPX regulates carcinogenesis will likely lead to the development of new therapeutic approaches.

Abstract

Homeobox genes are master regulators of morphogenesis and differentiation by acting at the top of genetic hierarchies and their deregulation is associated with a variety of human diseases. They usually contain a highly conserved sequence that codes for the homeodomain of the protein, a specialized motif with three α helices and an N-terminal arm that aids in DNA binding. However, one homeodomain protein, HOPX, is unique among its family members in that it lacks the capacity to bind DNA and instead functions by interacting with transcriptional regulators. HOPX plays crucial roles in organogenesis and is expressed in both embryonic and adult stem cells. Loss of HOPX expression is common in cancer, where it functions primarily as a tumor suppressor gene. In this review, we describe the function of HOPX in development and discuss its role in carcinogenesis.

Intestinal alteration of α-gustducin and sweet taste signaling pathway in metabolic diseases is partly rescued after weight loss and diabetes remission

Carbohydrates and sweeteners are detected by the sweet taste receptor in enteroendocrine cells (EECs). This receptor is coupled to the gustducin G-protein, which α-subunit is encoded by GNAT3 gene. In intestine, the activation of sweet taste receptor triggers a signaling pathway leading to GLP-1 secretion, an incretin hormone. In metabolic diseases, GLP-1 concentration and incretin effect are reduced while partly restored after Roux-en-Y gastric bypass (RYGB). We wondered if the decreased GLP-1 secretion in metabolic diseases is caused by an intestinal defect in sweet taste transduction pathway. In our RNA-sequencing of EECs, GNAT3 expression is decreased in patients with obesity and type 2 diabetes compared with normoglycemic obese patients. This prompted us to explore sweet taste signaling pathway in mice with metabolic deteriorations. During obesity onset in mice, Gnat3 expression was downregulated in EECs. After metabolic improvement with enterogastro anastomosis surgery in mice (a surrogate of the RYGB in humans), the expression of Gnat3 increased in the new alimentary tract and glucose-induced GLP-1 secretion was improved. To evaluate if high-fat diet-induced dysbiotic intestinal microbiota could explain the changes in the expression of sweet taste α-subunit G-protein, we performed a fecal microbiota transfer in mice. However, we could not conclude if dysbiotic microbiota impacted or not intestinal Gnat3 expression. Our data highlight that metabolic disorders were associated with altered gene expression of sweet taste signaling in intestine. This could contribute to impaired GLP-1 secretion that is partly rescued after metabolic improvement.NEW & NOTEWORTHY Our data highlighted 1) the sweet taste transduction pathway in EECs plays pivotal role for glucose homeostasis at least at gene expression level; 2) metabolic disorders lead to altered gene expression of sweet taste signaling pathway in intestine contributing to impaired GLP-1 secretion; and 3) after surgical intestinal modifications, increased expression of GNAT3, encoding α-gustducin contributed to metabolic improvement.

Involvement of PP2A methylation in the adipogenic differentiation of bone marrow-derived mesenchymal stem cell

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are multipotent stem cells with ability to self-replicate and differentiate into mesodermal derivatives, such as adipocytes and osteoblasts. BM-MSCs are a critical component of the tumour microenvironment. They support tumour progression by recruiting additional BM-MSCs and by differentiating into myofibroblasts (also called cancer-associated fibroblasts). Protein phosphatase 2A (PP2A) is an essential serine/threonine protein phosphatase that regulates a broad range of cellular signalling. PP2A forms a heterotrimer to dephosphorylate specific substrates. The reversible methylesterification (methylation) of Leu309 in the catalytic subunit of PP2A (PP2Ac) regulates biogenesis of the PP2A holoenzyme. It is unknown whether the methylation of PP2Ac plays a role in BM-MSC differentiation. Our experiments determined that protein levels of PP2A subunits and PP2A methyltransferase (LCMT-1) are significantly altered during differentiation. PP2Ac methylation levels in BM-MSCs decrease over time in response to an adipogenic differentiation stimulus. However, blockage of PP2A demethylation using the PP2A dimethyl-esterase inhibitors enhanced adipocyte differentiation. This suggests that PP2Ac demethylation is involved in adipocyte differentiation resistance. The results of our study provide a greater understanding of the regulation of BM-MSCs differentiation by PP2A holoenzyme.

Cell death as a result of calcium signaling modulation: A cancer-centric prospective

Calcium ions (Ca²⁺) and the complex regulatory system governed by Ca²⁺ signaling have been described to be of crucial importance in numerous aspects related to cell life and death decisions, especially in recent years. The growing attention given to this second messenger is justified by the pleiotropic nature of Ca²⁺-binding proteins and transporters and their consequent involvement in cell fate decisions. A growing number of works highlight that deregulation of Ca²⁺ signaling and homoeostasis is often deleterious and drives pathological conditions; in particular, a disruption of the main Ca²⁺-mediated death mechanisms may lead to uncontrolled cell growth that results in cancer. In this work, we review the latest useful evidence to better understand the complex network of pathways by which Ca²⁺ regulates cell life and death decisions.

Doublecotin-Like Kinase 1 Increases Chemoresistance of Colorectal Cancer Cells through the Anti-Apoptosis Pathway

Background

Colorectal Cancer (CRC) is the third most common cancer diagnosed and the second leading cause of cancer-related deaths in the United States. Cancer Stem Cells (CSCs) are believed to be the primary reason for the recurrence of CRC. Specific stem cell marker, doublecortin-like kinase 1 (DCLK1) plays critical roles in the tumorigenesis and progression of CRC. Up-regulation of DCLK1 is correlated with poor prognosis. Whether DCLK1 is correlated with enhanced chemoresistance of CRC cells is unclear. We aim to reveal the association of DCLK1 with chemoresistance of CRC cells and the underlying molecular mechanisms.

Methods

Stable DCLK1 over-expression cells (DCLK1+) were established using the HCT116 cells (WT). DCLK1+ and WT cells were treated with 5-Fluorouracil (5-Fu) at different doses for 24 or 48 hours. MTT assay was used to evaluate cell viability and IC50 of 5-Fu was determined. Quantitative real-time PCR was applied to determine the gene expression of caspase-3 (casp-3), casp-4, and casp-10. Cleaved casp-3 expression was investigated using Western blot and immunofluorescence.

Results

Our results demonstrated that IC50 of 5-Fu for the DCLK1+ cells was significantly higher than that of the WT cells for both 24 and 48-hour treatment (p=0.002 and 0.048 respectively), indicating increased chemoresistance of the DCLK1+ cells. Gene expression of casp-3, casp-4, and casp-10 were significantly inhibited in the DCLK1+ cells after 5-Fu treatment compared to the WT cells (p=7.616e-08, 1.575e-05 and 5.307e-08, respectively). Cleaved casp-3 amount and casp-3 positive cells were significantly decreased in the DCLK1+ cells after 5-Fu treatment compared to the WT cells (p=0.015).

Conclusions

In conclusion, our results demonstrated that DCLK1 overexpression enhanced the chemoresistance of CRC cells to 5-Fu treatment by suppressing gene expression of key caspases in the apoptosis pathway and activation of the apoptosis pathway. DCLK1 can be an intriguing therapeutic target for the effective treatment of CRC patients.

Doublecortin-like kinase 1 compromises DNA repair and induces chromosomal instability

Doublecortin-like kinase 1 (DCLK1) is a serine/threonine-kinase with two doublecortin (DCX) domains. DCLK1 is associated with microtubules via DCX domains and regulates microtubule polymerization. DCLK1 is known to be expressed in cancer stem cells and provides cancer cells with tumor-initiating capacity. Accumulating clinical evidence supports that DCLK1 is associated with tumor aggressiveness and is an important prognostic marker in various human cancers. However, the mechanism, by which DCLK1 causes oncogenesis, is not yet elucidated. In this study, we showed that DCLK1 empowers human mammary epithelial MCF10A cells to form spheres under floating condition in serum-free medium, which are reminiscent of mammospheres formed by mammary epithelial stem cells. We demonstrated that DCLK1 causes chromatin instability in MCF10A cells. DCLK1 impairs DNA repairs in human colon cancer HCT116 and lung cancer H1299 cells. The kinase-negative DCLK1 mutant and the mutant that is not associated with microtubules compromise DNA repair. In conclusion, DCLK1 interferes with DNA repair and induces tumorigenesis through genomic instability and this function is independent of the kinase activity and the regulation of microtubules.

Identification of anti-tumour biologics using primary tumour models, 3-D phenotypic screening and image-based multi-parametric profiling

Background

Monolayer cultures of immortalised cell lines are a popular screening tool for novel anti-cancer therapeutics, but these methods can be a poor surrogate for disease states, and there is a need for drug screening platforms which are more predictive of clinical outcome. In this study, we describe a phenotypic antibody screen using three-dimensional cultures of primary cells, and image-based multi-parametric profiling in PC-3 cells, to identify anti-cancer biologics against new therapeutic targets.

Methods

ScFv Antibodies and designed ankyrin repeat proteins (DARPins) were isolated using phage display selections against primary non-small cell lung carcinoma cells. The selected molecules were screened for anti-proliferative and pro-apoptotic activity against primary cells grown in three-dimensional culture, and in an ultra-high content screen on a 3-D cultured cell line using multi-parametric profiling to detect treatment-induced phenotypic changes. The targets of molecules of interest were identified using a cell-surface membrane protein array. An anti-CUB domain containing protein 1 (CDCP1) antibody was tested for tumour growth inhibition in a patient-derived xenograft model, generated from a stage-IV non-small cell lung carcinoma, with and without cisplatin.

Results

Two primary non-small cell lung carcinoma cell models were established for antibody isolation and primary screening in anti-proliferative and apoptosis assays. These assays identified multiple antibodies demonstrating activity in specific culture formats. A subset of the DARPins was profiled in an ultra-high content multi-parametric screen, where 300 morphological features were measured per sample. Machine learning was used to select features to classify treatment responses, then antibodies were characterised based on the phenotypes that they induced. This method co-classified several DARPins that targeted CDCP1 into two sets with different phenotypes. Finally, an anti-CDCP1 antibody significantly enhanced the efficacy of cisplatin in a patient-derived NSCLC xenograft model.

Conclusions

Phenotypic profiling using complex 3-D cell cultures steers hit selection towards more relevant in vivo phenotypes, and may shed light on subtle mechanistic variations in drug candidates, enabling data-driven decisions for oncology target validation. CDCP1 was identified as a potential target for cisplatin combination therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0415-0) contains supplementary material, which is available to authorized users.

Calcium and mitochondria in the regulation of cell death

The calcium ion has long been known to play an important role in cell death regulation. Hence, necrotic cell death was early associated with intracellular Ca(2+) overload, leading to mitochondrial permeability transition and functional collapse. Subsequent characterization of the signaling pathways in apoptosis revealed that Ca(2+)/calpain was critically involved in the processing of the mitochondrially localized, Apoptosis Inducing Factor. More recently, the calcium ion has been demonstrated to play important regulatory roles also in other cell death modalities, notably autophagic cell death and anoikis. In this review, we summarize current knowledge about the mechanisms involved in Ca(2+) regulation of these various modes of cell death with a focus on the importance of the mitochondria.