Fueling Cell Invasion through Extracellular Matrix

Abstract

Cell invasion through extracellular matrix (ECM) has pivotal roles in cell dispersal during development, immune cell trafficking, and cancer metastasis. Many elegant studies have revealed the specialized cellular protrusions, proteases, and distinct modes of migration invasive cells use to overcome ECM barriers. Less clear, however, is how invasive cells provide energy, specifically ATP, to power the energetically demanding membrane trafficking, F-actin polymerization, and actomyosin machinery that mediate break down, remodeling, and movement through ECMs. Here, we provide an overview of the challenges of examining ATP generation and delivery within invading cells and how recent studies using diverse invasion models, experimental approaches, and energy biosensors are revealing that energy metabolism is an integral component of cell invasive behavior that is dynamically tuned to overcome the ECM environment.

Keywords: Cell invasion; adaptive ATP metabolism; extracellular matrix; glycolysis; mitochondrial localization; oxidative phosphorylation.

Figure 1.

A schematic diagram of energy metabolism that can lead to ATP production within an invading cell. One molecule of glucose (6C) is broken down into two molecules of pyruvate (3C) by glycolysis to produce two molecules of ATP. The pyruvate can be converted into lactate under aerobic and anaerobic conditions or be transported into mitochondria to be converted into acetyl coA (2C) which is fed into the tricarboxylic acid (TCA) cycle to generate a proton gradient and produce 32 molecules of ATP via electron transport chain complex V. In some cases, glutamate and fatty acids can also be incorporated into mitochondrial metabolism to generate ATP (gray arrows). TCA cycle: tricarboxylic acid cycle, 2-OG: 2-oxoglutarate, OXPHOS: oxidative phosphorylation.

Figure 2.

Mitochondria provide ATP via OXPHOS at sites invasion. (A) The C. elegans anchor cell (left panel, magenta) is in contact with an intact basement membrane (green, arrow, visualized with laminin::GFP) just prior to invasion. Prior to and during invasion through basement membrane (middle and right panels), mitochondria enrich within the anchor cell at the site of invasion (visualized by Mitotracker, arrowheads) as do elevated levels of ATP (visualized by ATeam, arrowhead). Figure adapted with permission from Kelley et al. 2019, scale bar 5μm. (B) A custom transwell assay was used with a Seahorse XF analyzer to determine the energy metabolism in the cell body versus the pseudopod of SKOV-3 ovarian cancer cells. The transwell also allowed for biochemical isolation of the cell body and pseudopod. This analysis revealed the pseudopod contains higher AMPK and ATP levels and that OXPHOS generates the ATP within the pseudopod. In contrast, in the cell body there is lower ATP and AMPK levels and the ATP is primarily generated by aerobic glycolysis. pAMPK: phosphorylated AMP kinase, OXPHOS: oxidative phosphorylation.

Figure 3.

Invading cells adapt ATP metabolism to overcome distinct ECM barriers. (A) In response to stiff matrices, invading pancreatic cancer cells localize fused mitochondria in invading protrusions and increase ATP production. In addition, through an integrin-mediated mechanosensitive mechanism, YAP enters the nucleus and leads to the transcription of creatine kinase, which mediates the transfer of phosphate onto creatine—an energy storage molecule that diffuses more readily than ATP. Creatine kinase can then later catalyze the recovery of ATP from phosphocreatine. (B) During collective migration, leader cells bear the energetically demanding role of degrading and remodeling ECM. When the leader cell’s ATP:ADP ratio drops to a low level, the leader cell halts in its invasion, and then is replaced by a follower cell with a high ATP:ADP ratio that resumes invasion. (C) During C. elegans anchor cell invasion, small invadopodia depress and breach the basement membrane through a combination of MMP-mediated basement membrane degradation and physical displacement. In the absence of MMPs, more mitochondria localize to the invasive front and deliver high levels of ATP to fuel the formation of a large F-actin based protrusion that breaches the basement membrane solely through physical displacement. ECM: extracellular matrix