Chronic acidosis in the tumour microenvironment selects for overexpression of LAMP2 in the plasma membrane

Abstract

Early cancers are avascular and hence, profoundly acidic. Pre-malignant cells must adapt to acidosis to thrive in this hostile microenvironment. Here, we investigate MCF-7 cells that are adapted to grow in acidic conditions using SILAC proteomics and we reveal a significant upregulation of lysosomal proteins. Prominent among these is LAMP2 that functions to protect lysosomal membranes from acid proteolysis. LAMP2 upregulation by acidosis is confirmed both in vitro and in vivo. Furthermore, we show that the depletion of LAMP2 is sufficient to increase acidosis-mediated toxicity. In breast cancer patient samples, there is a high correlation of LAMP2 mRNA and protein expression with progression. We also observe that LAMP2 is located at the plasma membrane in clinical samples and this redistribution is acid-induced in vitro. Our findings suggest a potential adaptive mechanism, wherein cells chronically exposed to an acidic environment translocate lysosomal proteins to their surface, thus protecting the plasmalemma from acid-induced hydrolysis.

Phenotypic changes of acid-adapted cancer cells push them toward aggressiveness in their evolution in the tumor microenvironment

“…In solid tumors such as breast cancer, hyperplastic epithelial cells grow into ductal lumens pushing them further from the stromal vasculature, leading to selection for a glycolytic phenotype through hypoxia and consequently increased acidity that leads to acid adapted phenotype, as we showed previously for the cells at the center of DCIS samples. 15 This acidic niche can be re-created in later stages through hard-wired glycolysis (Warburg effect) that generates acid-producing cancer cells. Notably, these appear to emerge at the leading edge of invading tumors.…”

“…One of these, the highly glycosylated lysosomal-associated membrane protein, LAMP2, is of particular interest as this heavily glycosylated protein serves to protect the lysosomal membranes from acid hydrolysis and plays a critical role in autophagy. 14,15 We recently unraveled a mechanism by which cancer cells use a strategy to protect themselves form extracellular acidosis, that is "borrowed" from a strategy that lysosomes use to protect their membranes against high acidity of their lumen (pH»4-5). This borrowed mechanism involves redistribution of LAMP2 to the cell surface, which we hypothesize serves to protect cells against extracellular acidosis inside the tumor.…”

“…In clinical breast cancer specimens, we observed that LAMP2 expression increased significantly with grade and that it appeared to redistribute from lysosomes to the cell surface, especially in poorly perfused areas and those expressing the glucose transporter, GLUT1, which are expected to be acidic. 15 The focus of this article is to illustrate some of the phenotypic changes that are associated with adaptation of cancer cells to chronic intratumoral acidosis. This is within the context of a broader investigation to define the role of the microenvironment on cancer evolution and therapy.…”

Gene expression changes in bioceramic paste-treated human dental pulp cells

“…LAMP2 is a member of a family of membrane glycoproteins and may play a role in tumor cell metastasis, and it may also act in the protection, maintenance, and adhesion of the lysosome (14,15). LAMP2 is a lysosomal marker expressed by the autophagic vacuoles that constitutes the autophagic-lysosomal system of odontoblasts (16).…”

Lysosomal protein relocation as an adaptation mechanism to extracellular acidosis

“…4,5 Importantly, neutralizing acidity can inhibit metastasis and augment the response to anti-tumor immune therapies, including checkpoint blockade and adoptive cell transfer. 5 In our recent paper 6 we investigated the acid adaptations in MCF-7 breast cancer cells using shotgun proteomics. In our experiment, cancer cells were adapted to growth in acidic conditions (media with pH 6.7) for more than 20 passages (>2 months), after which their growth rate in acidic conditions was identical to that of the parental cells at neutral pH.…”