Princeton researchers discover previously unknown organelles that play a role in bone metastases

Some of Princeton’s leading cancer researchers were surprised to find that what they thought was a straightforward investigation of how cancer spreads throughout the body – metastasizes – revealed evidence of liquid-liquid phase separations: the new field of research in biology that studies the degree of liquid. drops of living matter melt into each other, similar to movements seen in a lava lamp or in liquid mercury.

We believe this is the first time that phase separation has been involved in cancer metastases. “

Yibin Kang, Warner-Lambert / Parke-Davis Professor of Molecular Biology

He is the lead author of a new article on the cover of the current issue of Cellular biology of nature.

Not only does their work link phase separations to cancer research, but the fusion of the spots has been found to create more than the sum of their parts, self-assembling into a hitherto unknown organelle (essentially an organ of the cell).

The discovery of a new organelle is revolutionary, Kang said. He compared it to the discovery of a new planet within our solar system. “Some organelles that we’ve known for 100 years or more, and then all of a sudden we found a new one!”

This will change some fundamental perceptions of what a cell is and what it does, said Mark Esposito, a 2017 doctoral student, former student and current postdoc in Kang’s lab who is the first author of the new article. “Everyone goes to school, and they learn ‘Mitochondria are the powerhouse of the cell,’ and a few other things about a few organelles, but now our classic definition of what’s inside of a cell, the way a cell organizes itself and controls its behavior, begins to change, ”he said. “Our research marks a very concrete step forward in this regard.”

The work was born out of collaborations between researchers in the laboratories of three Princeton professors: Kang; Ileana Cristea, professor of molecular biology and leading specialist in living tissue mass spectroscopy; and Cliff Brangwynne, June K. Wu ’92 professor of chemical and biological engineering and director of the Princeton Bioengineering Initiative, which pioneered the study of phase separation in biological processes.

“Ileana is a biochemist, Cliff is a biophysicist and an engineer, and I am a cancer biologist – a cell biologist,” Kang said. “Princeton is just a wonderful place where people can connect and collaborate. We have a very small campus. All of the science departments are right next to each other. Ileana’s lab is actually on the same floor as Lewis Thomas’s mine! These very close relationships, among very diverse fields of research, allow us to bring technologies from many different angles, and to make breakthroughs in understanding the mechanisms of metabolism in cancer – its progression, metastasis and immune response. – and also to come up with new ways to target it. “

The latest breakthrough, featuring the still-unknown organelle, adds new understanding to the role of the Wnt signaling pathway, a system whose discovery led to the 1995 Nobel Prize for Eric Wieschaus, Princeton Squibb professor of molecular biology and professor at the Lewis -Sigler Institute for Integrative Genomics. The Wnt pathway is vital for embryonic development in countless organisms, from tiny invertebrate insects to humans. Wieschaus discovered that cancer can co-opt this pathway, essentially corrupting its ability to grow as quickly as embryos must, to develop tumors.

Subsequent research revealed that the Wnt signaling pathway plays several roles in healthy bone growth as well as in cancer metastasizing into bone. Kang and his colleagues were studying the complex interaction between Wnt, a signaling molecule called TGF-b, and a relatively unknown gene named DACT1 when they discovered this new organelle.

Think of it like panic shopping before a storm, Esposito said. Buying bread and milk before a blizzard – or hoarding hand sanitizer and toilet paper when a pandemic looms on the horizon – aren’t just human traits, it turns out. They also occur at the cellular level.

Here’s how it works: The panicked buyer is DACT1, and the blizzard (or pandemic) is TGF-ß. The disinfectant for bread and hands is casein kinase 2 (CK2), and in the presence of a storm, DACT1 catches as much as possible, and the newly discovered organelle sequesters them. By accumulating CK2, the buyer prevents other people from making sandwiches and sanitizing their hands, that is, preventing the proper functioning of the Wnt path.

Through a series of detailed and complex experiments, the researchers piece together the story: Bone tumors initially induce Wnt signaling, to disseminate (spread) through bone. Next, TGF-b, which is abundant in bones, inspires panicky shopping, suppressing Wnt signaling. The tumors then stimulate the growth of osteoclasts, which shed old bone tissue. (Healthy bones are constantly replenished in a two-part process: osteoclasts rub a layer of bone, then osteoblasts rebuild the bone with new material.) This further increases the concentration of TGF-b, which further results in more DACT1 hoarding and subsequent Wnt suppression was found to be important in other metastases.

By discovering the roles of DACT1 and this organelle, Kang and his team found possible new targets for cancer drugs. “For example, if we have a way to disrupt the DACT1 complex, maybe the tumor will spread, but it can never ‘grow’ into a potentially fatal metastasis. This is hope, ”Kang said.

Kang and Esposito recently co-founded KayoThera to further develop drugs for patients with advanced or metastatic cancer, based on their work together in Kang’s lab. “The type of fundamental study that Mark performs both presents groundbreaking scientific discoveries and can lead to medical breakthroughs as well,” Kang said.

Researchers have found that DACT1 plays many other roles as well, which their team are just beginning to explore. Collaboration in mass spectrometry with Cristea’s team has revealed more than 600 different proteins in the mysterious organelle. Mass spectrometry allows scientists to discover the exact components of almost any substance imaged on a microscope slide.

“This is a more dynamic signaling node than just controlling Wnt and TGF-b.” said Esposito. “This is just the tip of the iceberg in a new area of ​​biology.”

This bridge between phase separations and cancer research is still in its infancy, but it is already showing great potential, said Brangwynne, co-author of the article.

“The role that biomolecular condensates play in cancer – both its genesis but especially its spread by metastasis – is still poorly understood,” he said. “This study provides new insights into the interaction of cancer signaling pathways and condensate biophysics, and it will open up new therapeutic avenues.”