Acidosis and proteolysis in the tumor microenvironment

Focus on the morphogenesis, fate and the role in tumor progression of multivesicular bodies

Multivesicular bodies (MVBs) are endosome organelles that are gradually attracting research attention. Initially, MVBs were considered as important components of the endosomal-lysosomal degradation pathway. In recent years, with an increase in extracellular vesicle (EV) research, the biogenesis, fate, and pathological effects of MVBs have been increasingly studied. However, the mechanisms by which MVBs are sorted to the lysosome and plasma membrane remain unclear. In addition, whether the trafficking of MVBs can determine whether exosomes are released from cells, the factors are involved in cargo loading and regulating the fate of MVBs, and the roles that MVBs play in the development of disease are unknown. Consequently, this review focuses on the mechanism of MVB biogenesis, intraluminal vesicle formation, sorting of different cargoes, and regulation of their fate. We also discuss the mechanisms of emerging amphisome-dependent secretion and degradation. In addition, we highlight the contributions of MVBs to the heterogeneity of EVs, and their important roles in cancer. Thus, we attempt to unravel the various functions of MVBs in the cell and their multiple roles in tumor progression.

Matrix Metalloproteinases' Role in Tumor Microenvironment

Cancer cells evolve in the tumor microenvironment (TME) by the acquisition of characteristics that allow them to initiate their passage through a series of events that constitute the metastatic cascade. For this purpose, tumor cells maintain a crosstalk with TME non-neoplastic cells transforming them into their allies. "Corrupted" cells such as cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and tumor-associated neutrophils (TANs) as well as neoplastic cells express and secrete matrix metalloproteinases (MMPs). Moreover, TME metabolic conditions such as hypoxia and acidification induce MMPs' synthesis in both cancer and stromal cells. MMPs' participation in TME consists in promoting events, for example, epithelial-mesenchymal transition (EMT), apoptosis resistance, angiogenesis, and lymphangiogenesis. MMPs also facilitate tumor cell migration through the basement membrane (BM) and extracellular matrix (ECM). The aim of the present chapter is to discuss MMPs' contribution to the evolution of cancer cells, their cellular origin, and their influence in the main processes that take place in the TME.

Spatio-temporal modeling and live-cell imaging of proteolysis in the 4D microenvironment of breast cancer

Cells grown in three dimensions (3D) within natural extracellular matrices or synthetic scaffolds more closely recapitulate the phenotype of those cells within tissues in regard to normal developmental and pathobiological processes. This includes degradation of the surrounding stroma as the cells migrate and invade through the matrices. As 3D cultures of tumor cells predict efficacy of, and resistance to, a wide variety of cancer therapies, we employed tissue-engineering approaches to establish 3D pathomimetic avatars of human breast cancer cells alone and in the context of both their cellular and pathochemical microenvironments. We have shown that we can localize and quantify key parameters of malignant progression by live-cell imaging of the 3D avatars over time (4D). One surrogate for changes in malignant progression is matrix degradation, which can be localized and quantified by our live-cell proteolysis assay. This assay is predictive of changes in spatio-temporal and dynamic interactions among the co-cultured cells and changes in viability, proliferation, and malignant phenotype. Furthermore, our live-cell proteolysis assay measures the effect of small-molecule inhibitors of proteases and kinases, neutralizing or blocking antibodies to cytokines and photodynamic therapy on malignant progression. We suggest that 3D/4D pathomimetic avatars in combination with our live-cell proteolysis assays will be a useful preclinical screening platform for cancer therapies. Our ultimate goal is to develop 3D/4D avatars from an individual patient's cancer in which we can screen "personalized medicine" therapies using changes in proteolytic activity to quantify therapeutic efficacy.

δ-secretase in neurodegenerative diseases: mechanisms, regulators and therapeutic opportunities

Mammalian asparagine endopeptidase (AEP) is a cysteine protease that cleaves its protein substrates on the C-terminal side of asparagine residues. Converging lines of evidence indicate that AEP may be involved in the pathogenesis of several neurological diseases, including Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. AEP is activated in the aging brain, cleaves amyloid precursor protein (APP) and promotes the production of amyloid-β (Aβ). We renamed AEP to δ-secretase to emphasize its role in APP fragmentation and Aβ production. AEP also cleaves other substrates, such as tau, α-synuclein, SET, and TAR DNA-binding protein 43, generating neurotoxic fragments and disturbing their physiological functions. The activity of δ-secretase is tightly regulated at both the transcriptional and posttranslational levels. Here, we review the recent advances in the role of δ-secretase in neurodegenerative diseases, with a focus on its biochemical properties and the transcriptional and posttranslational regulation of its activity, and discuss the clinical implications of δ-secretase as a diagnostic biomarker and therapeutic target for neurodegenerative diseases.

A mitochondria-targeted two-photon fluorescent probe for sensing and imaging pH changes in living cells

A novel two-photon pH probe, 3-benzimidazole-7-hydroxycoumarin (BHC), was designed and synthesized based on the structures of hydroxycoumarin and benzimidazole. BHC showed good linearity in the pH ranges of 3.30-5.40 (pKa = 4.20) and 6.50-8.30 (pKa = 7.20) at a maximum emission wavelength of 480 nm. BHC in acidic and alkaline media could be distinguished by an obvious spectral shift of the maximum absorption wavelength from 390 nm to 420 nm. In addition, BHC was well localized to mitochondria and successfully applied to one-photon and two-photon imaging of pH changes in the mitochondria of HeLa cells. The findings presented herein suggest that BHC can serve as an excellent fluorescent probe for selectively sensing mitochondrial pH changes with remarkable photostability and low cytotoxicity.

A mitochondrial-targetable dual functional near-infrared fluorescent probe to monitor pH and H2O2 in living cells and mice

A lower pH level and high hydrogen peroxide (H₂O₂) concentration in mitochondria is closely associated with a variety of diseases including cancer and inflammation. Thus, determination of changes in the level of acidic pH and H₂O₂ is of great importance and could provide new insights into the key functions under both physiological and pathological conditions. Herein, we present a novel mitochondria-targetable probe NIR-pH-H₂O₂, as the first near infrared (NIR) fluorescent small molecule, to monitor changes of endogenous pH (pk_a = 6.17) and H₂O₂ with high sensitivity, good compatibility and low cytotoxicity. Futhermore, it was successfully employed to monitor pH and H₂O₂ in a mouse acute inflammation model. These results demonstrate that NIR-pH-H₂O₂ is a novel bifunctional mitochondrial-targeted NIR probe to sense acidic pH and H₂O₂in vitro and in vivo, indicating its huge potential for the diagnosis of pH and H₂O₂-related diseases.

A lower pH level and high hydrogen peroxide (H₂O₂) concentration in mitochondria is closely associated with a variety of diseases including cancer and inflammation.

Increased proton-sensing receptor GPR4 signalling promotes colorectal cancer progression by activating the hippo pathway

Background

Colorectal cancer (CRC) is one of the high incidences tumours and is ranked second in cancer-related mortality. Even though great progress has been made, there are no effective therapeutic strategies for late stage and metastatic CRC patients. Acidity is one characteristic of the tumour microenvironment. However, how cancer cells respond to this acidic environment surrounding them remains largely unknown, especially in colorectal cancer.

Methods

Proton sensor receptor expression was analysed in GEO and TCGA datasets. The expression of GPR4 in CRC specimens was confirmed by western blotting and immunohistochemistry (IHC). The role of GPR4 in CRC progression was analysed both in vitro and in vivo. Pharmacological intervention, immunofluorescence and gene set enrichment analyses were performed to reveal the underlying molecular mechanisms of GPR4.

Findings

We found that GPR4 was upregulated in CRC samples. In addition, its high expression correlated with late stage tumours and poor overall survival in patients. Furthermore, loss-of-function assays proved that GPR4 promoted CRC carcinogenesis and metastatic ability. Mechanistically, GPR4 was activated by extracellular protons in the tumour microenvironment and enhanced RhoA activation and F-actin rearrangement, leading to LATS activity inhibition, YAP1 nuclear translocation and oncogene transcription.

Interpretation

The expression of GPR4 is upregulated in colorectal cancer and is associated with shorter overall survival time in CRC patients. These findings reveal the novel roles of GPR4 in CRC progression and suggest GPR4 might be a new therapeutic target for CRC treatment.