Researchers have identified a previously unknown backup system that lets mammalian cells produce the essential amino acid cysteine even when the pathways long considered indispensable for this task are switched off. The finding overturns a longstanding assumption about how cells keep themselves alive under metabolic stress.
Cysteine is critical for building proteins and defending against oxidative damage, and cells were thought to depend on a single, well-defined route to make it. The new work shows that when that route is blocked, a hidden alternative can take over, allowing cells to survive conditions that were previously believed to be lethal.
The same survival mechanism may be co-opted by cancer cells, helping them withstand therapies aimed at disrupting cysteine production or metabolism. That raises the possibility of designing treatments that also disable the backup pathway, potentially making cancer cells far more vulnerable than they are today.