Just as plastic tips protect the ends of shoelaces and keep them from fraying when we tie them, molecular tips called telomeres protect the ends of chromosomes and keep them from fusing when cells continually divide and duplicate their DNA. But while losing the plastic tips may lead to messy laces, telomere loss may lead to cancer.

Salk Institute scientists studying the relationship of telomeres to cancer made a surprising discovery: a cellular recycling process called autophagy — generally thought of as a survival mechanism — actually promotes the death of cells, thereby preventing cancer initiation.

The work, which appeared in the journal Nature on January 23, 2019, reveals autophagy to be a completely novel tumor-suppressing pathway and suggests that treatments to block the process in an effort to curb cancer may unintentionally promote it very early on.

“These results were a complete surprise,” says Jan Karlseder, a professor in Salk’s Molecular and Cell Biology Laboratory and the senior author of the paper. “There are many checkpoints that prevent cells from dividing out of control and becoming cancerous, but we did not expect autophagy to be one of them.”

Each time cells duplicate their DNA to divide and grow, their telomeres get a little bit shorter. Once telomeres become so short that they can no longer effectively protect chromosomes, cells get a signal to stop dividing permanently. But occasionally, due to cancer-causing viruses or other factors, cells don’t get the message and keep on dividing. With dangerously short or missing telomeres, cells enter a state called crisis, in which the unprotected chromosomes can fuse and become dysfunctional — a hallmark of some cancers.

Read more at Salk Institute