A novel mechanism that regulates cellular injury by phagocytes during inflammation

December 21, 2018


Lysosomes are filled with more than 50 different hydrolytic enzymes, which are capable of digesting most cellular components. Notably, activated phagocytes secrete lysosomal enzymes with cytotoxic activity against external pathogens or tumor cells, inducing heterolysis. However, the molecular mechanisms that regulate lysosomal exocytosis by phagocytes remain largely unknown. In several types of cells, transmembrane proteins possessing C2 domains, such as Munc13-4 and synaptotagmin-VII, are present on the lysosomal membrane and known to regulate Ca2+-triggered lysosomal exocytosis. C2 domains mediate Ca2+-dependent binding to phosphatidylserine (PS) in the inner leaflet of the plasma membrane, which is a critical process for membrane fusion. Myoferlin is a type II transmembrane protein with seven C2 domains in its cytoplasmic region. The first C2 domain (C2A domain) binds PS in a calcium-dependent manner. Myoferlin was first identified as a protein expressed in the plasma membrane of myoblasts undergoing fusion and has since been implicated in the repair of injured plasma membranes. Injury-induced Ca2+ influx through membrane lesions triggers endocytosis and the generation of endocytosed vesicles expressing myoferlin, which fuse with the injured membrane to yield a membrane patch. This characteristic of myoferlin led to the hypothesis that it may be a regulator of calcium-dependent lysosomal exocytosis by phagocytes.


We found that myoferlin was highly expressed by macrophages and localized to lysosomes. Analysis of transformed cells expressing shRNA against myoferlin demonstrated that myoferlin knockdown cells contained significantly more lysosomes and cytoplasmic vesicles filled with debris and additional membranous materials compared with the control cells (Figure 2). The amount of lysosomal enzyme secreted after calcium stimulation was significantly impaired by myoferlin knockdown, but was restored by re-expressing myoferlin protein. Similarly, macrophages from myoferlin-/- mice also displayed accumulation of lysosomes and reduction of lysosomal enzyme secretion after various calcium stimuli. The injection of Escherichia coli BioParticles into control mice increased the amount of the lysosomal enzymes in the peritoneal fluid (ascites), which was inhibited in myoferlin-/- mice (Figure 3). Additionally, the peritoneal fluid had a cytotoxic effect when added into culture media of tumor cells, which was also attenuated in myoferlin-/- mice, consistent with the amount of lysosomal enzyme present.

[Significance and future prospects]

This study reveals that myoferlin is a Ca2+-dependent regulator of lysosomal exocytosis by phagocytes. As autolysosomes filled with debris accumulated in the myoferlin knockdown cells, we speculated that myoferlin on autolysosomes might promote expelling of indigestible debris generated inside autolysosomes via exocytosis. Phagocytes have a potent cytotoxic capacity induced by antibodies against target cells (e.g., pathogens and tumor cells), known as antibody-dependent cell-mediated cytotoxicity (ADCC). These antibodies activate Fc receptors to trigger signaling pathway that induces Ca2+-dependent lysosomal exocytosis. Notably, neutrophils have particularly strong ADCC activity, during which they secrete large amounts of cytotoxic molecules, including hydrolytic enzymes, oxidative metabolites, and host defense peptides such as defensins. It would therefore be useful to study whether myoferlin also regulates the release of these molecules from neutrophils. Moreover, our demonstration that myoferlin deficiency decreased the cytotoxicity of phagocytes is clinically important and may facilitate the development of novel therapeutic approaches based on myoferlin-mediated lysosomal exocytosis.

Kanazawa University

Related Tumor Cells Articles from Brightsurf:

A more sensitive way to detect circulating tumor cells
Breast cancer is the most frequently diagnosed cancer in women, and metastasis from the breast to other areas of the body is the leading cause of death in these patients.

Cancer researchers train white blood cells to attacks tumor cells
Scientists at the National Center for Tumor Diseases Dresden (NCT/UCC) and Dresden University Medicine, together with an international team of researchers, were able to demonstrate that certain white blood cells, so-called neutrophil granulocytes, can potentially - after completing a special training program -- be utilized for the treatment of tumors.

How to prevent the spread of tumor cells via the lymph vessels
Scientists from the German Cancer Research Center and the Mannheim Medical Faculty of the University of Heidelberg identified a new way to block the dangerous spread of tumor cells via lymphatic vessels.

The CNIO reprograms CRISPR system in mice to eliminate tumor cells without affecting healthy cells
CNIO researchers destroyed Ewing's sarcoma and chronic myeloid leukaemia tumor cells by using CRISPR to cut out the fusion genes that cause them.

Feeding off fusion or the immortalization of tumor cells
Despite all recent progress, cancer remains one of the deadliest human diseases.

How do tumor cells divide in the crowd?
Scientists led by Dr. Elisabeth Fischer-Friedrich, group leader at the Excellence Cluster Physics of Life (PoL) and the Biotechnology Center TU Dresden (BIOTEC) studied how cancer cells are able to divide in a crowded tumor tissue and connected it to the hallmark of cancer progression and metastasis, the epithelial-mesenchymal transition (EMT).

How tumor cells evade the immune defense
Scientists are increasingly trying to use the body's own immune system to fight cancer.

Engineered immune cells recognize, attack human and mouse solid-tumor cancer cells
CAR-T therapy has been used successfully in patients with blood cancers such as lymphoma and leukemia.

New pathway to attack tumor cells identified
A study led by the Institut de Neurociències (INc-UAB) describes a new strategy to tackle cancer, based on inducing a potent stress in tumor causing cell destruction by autophagy.

Nutrient deficiency in tumor cells attracts cells that suppress the immune system
A study led by IDIBELL researchers and published this week in the American journal PNAS shows that, by depriving tumor cells of glucose, they release a large number of signaling molecules.

Read More: Tumor Cells News and Tumor Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.