FIGURE 1.

Overview of nutrient scavenging pathways in cancer cells. During cancer progression, cancer cells increase their energy and nutrient requirement to meet the demand of constant proliferation and sustain processes such as migration and invasion. For this, they use membrane trafficking pathways to scavenge nutrients already available. Macropinocytosis allows the bulk internalization of extracellular ATP as well as albumin and other nutrients. In a similar manner, receptor-mediated endocytosis is responsible for the uptake of receptors and their ligands that will be degraded in the lysosomes providing new building blocks to be reused. Examples are integrins that bind to ECM components, and megalin which binds to albumin in the extracellular environment. The internalized albumin can either bind to neonatal Fc receptor inside the endosomes and be recycled back to the plasma membrane, or degraded in the lysosomes. To access the pool of nutrients already available in the cell, cancer cells can hijack autophagy. Engulfed damaged organelles and protein aggregates can thus be broken down and degraded in the lysosomes for reuse. The altered metabolism during cancer progression results in increased MT1-MMP recycling, thus promoting cell invasion.