A solitary vessel floats languidly through space, enshrouded in calm silence. Suddenly, a massive laser blast pierces the darkness, slamming into the vessel and piercing a hole in its hull. Instant chaos ensues. Debris flies as anything not tethered in place is flung out into the void. Alarms sound and orders are hastily relayed as the vessel’s crew leaps into action to repair the breach and allay the damage. It’s a cinematic drama befitting Star Trek, or Battlestar Galactica. Or Dr. Susan Parkhurst’s lab in the Basic Sciences Division at Fred Hutch. In Dr. Parkhurst’s lab, the vessel is not a spaceship but a single-celled fly embryo, the laser fired not from an enemy ship but from a microscope controlled by researchers, the intent not destruction but to wound the cell in order to understand the process by which cells repair and recover from such damage. But in this process, controlled by the coordinated actions of proteins within the cells, who sounds the alarm? Who relays the orders? And who acts to repair the breach? In a new research article published in Plos Genetics, the Parkhurst Lab, led by postdoctoral fellow Dr. Mitsutoshi Nakamura and research technician Jeffrey Verboon, identifies an important new role for the insulin signaling pathway in coordinating the repair of laser-inflicted wounds.
“Numerous cell types in the body are subject to high levels of stress daily,” write the study’s authors. “These stresses … can cause ruptures in the plasma membrane and its underlying cytoskeleton, requiring a rapid repair program to avert further damage, prevent infection/death, and restore normal function.” When a cell is damaged, an orchestrated series of events is initiated to repair its membrane. First, extracellular calcium rushes in through the hole, serving as a signal that the membrane has been breached. The most urgent need is to patch the hole. New membrane is therefore rapidly deployed to the injury site to re-seal the cell. Membrane alone, though, is flimsy. So, as a final step, a ring of actin is constructed around the patched hole and subsequently constricts, rebuilding the cytoskeletal scaffolding that supports the cell membrane as it goes. While the general process is known, many of the proteins that carry out the steps of wound repair have yet to be discovered. Thus, the Parkhurst Lab sought to identify these missing links.
The researchers wondered whether the proteins responsible for wound repair were already present in the cell and ready to act, or whether, after wounding, they first needed to be produced by the processes of transcription and translation. By blocking each of these processes independently, they found that translation is required to initiate wound repair and transcription is required for its later steps. “We found that the cell repair system needs, and activates, the rapid expression of genes that are not usually expressed,” said co-lead author Dr. Mitsutoshi Nakamura. This was a surprising result, he noted, considering that transcription and translation take time, and that wound repair is completed within tens of minutes. The authors also viewed this finding as an opportunity to learn more – by identifying the genes that are transcribed following injury, they might be able to find the key players in the process. Thus, they performed a microarray analysis and identified a total of 80 genes whose transcription is rapidly turned up after laser wounding. While some of these made sense – such as those that regulate actin functions – several of the most strongly up-regulated genes were members of the insulin signaling pathway. The group tested these insulin-related genes further and found that they were indeed needed for proper repair, and that they seemed to activate multiple downstream proteins that help form and close the actin ring. The Parkhurst group now believes that, at an early step in the repair process, the damaged cell releases its own insulin-like peptide, which is used to activate insulin signaling and regulate actin dynamics during repair.
The insulin signaling pathway is very well known for its function to control blood sugar levels, and its mis-regulation is a key characteristic of diabetes. And while its role in cellular wound repair was a surprise, it did clarify a mystery in the literature. “While previous studies suggest that the diabetic condition disrupts cell wound repair, this disruption was thought to be a secondary effect, such as resulting from fragile membrane. Strikingly, our results [instead] suggest a direct role for insulin signaling”, said Dr. Nakamura. Moving forward, Dr. Nakamura believes this will not be the last surprise to come from the lab’s work. “What other unexpected molecular pathways, such as insulin signaling, are defined by the genes we identified in our screen?” he mused, signaling the lab’s continued interested in revealing new factors controlling this important and complex process.
This work was supported by National Institutes of Health.
Fred Hutch/UW Cancer Consortium member Susan Parkhurst contributed to this work.
Nakamura M, Verboon JM, Allen TE, Abreu-Blanco MT, Liu R, Dominguez ANM, Delrow JJ, Parkhurst SM. 2020. Autocrine insulin pathway signaling regulates actin dynamics in cell wound repair. PLoS Genet 16(12): e1009186. https://doi.org/ 10.1371/journal.pgen.1009186