A key signaling protein that helps suppress
inflammation and scarring in the liver has been discovered by scientists at the Sanford Burnham Prebys Medical Discovery Institute
Most cases of liver cancer develop after long-term viral infection,
chronic exposure to alcohol, or excessive accumulation of fat in the
liver due to obesity. The liver reacts to those insults by trying to
wall it off with scar tissue and calling in immune cells with
inflammatory signals. If cancer arises, the resulting inflammation then
stokes tumor progression.
The results, published in Cancer Cell
represent another foundational step towards better treatments for liver
‘A key signaling protein that helps suppress inflammation and scarring in the liver has been discovered by scientists.’
"Our findings are very important because they help predict which
patients will respond to vitamin D analogs," said Jorge Moscat, deputy director and professor in the NCI-designated Cancer Center and
co-senior author of the paper. "We show that those drugs' ability to
suppress liver damage requires p62, which in liver tumors is usually
absent from the cells that initiate the inflammatory cascade."
Moscat and Maria Diaz-Meco, also a professor in the Cancer
Center and co-senior author, have long been interested in p62, a
molecular communication hub in the cell. Their previous studies have
shown that high levels of p62 promote cancer. However, a recent
investigation in prostate cancer found that in the tumor's surroundings,
p62 dampens production of inflammatory signals that fuel cancer growth.
The new study looked at whether p62 has these opposing functions in
other types of cancer as well. Because they'd previously studied p62 in
liver cancer, they removed it from the cells that become its support
system--hepatic stellate cells. These cells, which make up a small
proportion of liver tissue, are tremendously important since they
normally store vitamin A and support liver regeneration.
Interestingly, in mice lacking p62 specifically in stellate cells,
they saw more liver inflammation and fibrosis and, when they were given a
chemical that causes liver cancer, more tumors.
"Whether p62 is pro- or anti-cancer appears to depend on the cell
type," explained Diaz-Meco. "In cancer cells, it's bad, but in
surrounding cells that feed the tumor, it's good."
Importantly, the team's analysis of patient samples revealed that
hepatic stellate cells from patients with liver cancer produce less p62
than normal liver tissue, confirming the relevance of their results to
The researchers wanted to know which of its opposing roles was most
important, so they turned off the gene for p62 throughout the body in
another set of mice. These mice also had more liver tumors than mice
with p62, showing that hepatic stellate cells play a key part in
This study also revealed that p62 interacts with the vitamin D
receptor, which returns stellate cells to their vitamin A-storing state.
When p62 is missing, the receptor can't do its job, so the cells
continue to produce pro-inflammatory signals.
"Vitamin D and its analogs may still help prevent cancer in patients
with hepatitis or fatty liver disease," commented Diaz-Meco. "At that
stage, enough p62 may still be present in stellate cells for the vitamin
D receptor to work."
"Since p62 is so important in preventing liver cancer, we're now
interested in why it disappears in stellate cells," said Moscat. "We
plan to explore that question, which may lead to ways to turn its
expression back on, which should block liver cancer progression."