New clues to how cancer-related proteins plasmin, thrombin lose inhibition

October 18, 2010

RICHLAND, Wash. -- A new technique that searches blood for the tiniest remnants of broken down proteins has revealed new information about how cells crank up cancer activators called proteases. The results improve researchers' understanding of the mechanics of breast cancer and point to where to look for possible indicators of early disease.

Appearing this week in PLoS ONE, the research shows previously unknown contributing factors to protease activation, which helps spread cancer: cancer cells almost completely chew up small protein pieces that normally put the brakes on two proteases known as plasmin and thrombin. The loss of these brakes -- known as protease inhibitors antiplasmin and antithrombin -- occur considerably more in blood from cancer patients compared to healthy persons' blood.

Although researchers have long known that proteases become activated by cancer, this work led by researchers at the Department of Energy's Pacific Northwest National Laboratory shows two new possible mechanisms how. This work was supported by the NIH National Center for Research Resources.

Future work that measures how these proteins function in early and late stage cancer patients might reveal useful biomarkers for diagnosis.

Losing it

Cancer is largely about losing control of a cell's tightly regulated life cycle. Growing unrestrained, cancers consume bodily resources such as energy and tissue. One protein that loses control in breast and other cancers, plasmin, encourages the breakdown of the tissue matrix that keeps cells strapped together. This allows cancer cells to spread to other parts of the body. However, researchers have yet to fully work out the molecular chain of events inside and outside cells that leads to overactive plasmin.

In this work, scientists examined cellular shrapnel for clues. As cancer retunes cells to its own nefarious ends, proteins normally in use get chopped up. The cast-off proteins could reveal how cancer flourishes, providing a better understanding of the disease and insights into how to attack it.

To investigate cellular shrapnel, the team acquired blood samples from 15 breast cancer patients that spanned cancer stages from I to III. They combined all 15 samples to increase the odds of finding useful information. They also collected blood from 15 control healthy volunteers and treated the samples in the same way.

To examine just the smallest-sized cast-off protein remnants, the researchers removed the blood cells and the dozen most abundant proteins from the blood. Then they collected only the smallest protein pieces, many of which are about a tenth the size of common human proteins. The researchers called this collection of degraded pieces the plasma degradome.

Using proteomics methods at EMSL, DOE's Environmental Molecular Sciences Laboratory on the PNNL campus, the team identified the protein fragments in the cancer and healthy degradomes. The fragments between samples differed significantly. For example, cancer blood held fragments from more than 70 different proteins that were chopped into more than 800 pieces. Healthy blood only held 50 different proteins cut up into more than 400 pieces. In addition, the complement of fragments overlapped some between the cancerous and healthy, but not entirely.

Broken brakes

Different sets of fragments could indicate that cancers found new ways to cut old proteins, but an analysis showed that this was not the case. The key distinction the researchers found was in how often certain proteins were cut at individual sites -- these differed tremendously. In addition, the proteins most likely to be chopped-up in the cancer samples seemed to fall into known cancer-related protein families.

"We were surprised because we expected random changes to the degradome," said lead author, PNNL biologist Yufeng Shen. "But instead we found a cluster of protein changes in very specific biological systems."

These biological systems included two proteases and their corresponding inhibitors -- plasmin and antiplasmin, thrombin and antithrombin -- which keep healthy cells growing properly.

When the researchers compared all the different pieces of plasmin found in the cancer samples to the healthy samples, two fragments stood out. The team found one of them, a cut-up Plg preactivation peptide, chopped seven times more often in the cancer sample than in the healthy sample. This would lead to an increase in plasmin activation in the cancer patients.

The other stand-out fragment arose from antiplasmin, and the scientists only found it in blood from cancer patients. Because antiplasmin normally prevents plasmin from destroying the environment around cells, the presence of the cut fragment meant plasmin was free to do damage.

The researchers found a similar situation with thrombin, a protease that helps blood vessels form. The cancer samples harbored fewer intact molecules of its inhibitor, antithrombin, allowing the cancer to build vessels to bring in nourishment.

AWOL Reserves

Normally, backup systems exist to deal with proteases that have gone wrong. But the scientists found evidence that the backup systems were damaged in the cancer samples as well. The team found fragments from three important backup systems: protein clusters that protect the extracellular matrix around cells; several key elements of the immune system that can scan for and kill cancer cells; and other proteins that normally suppress cells from turning cancerous.

Taken together, all these dysfunctional systems mean cells and their environment are helpless against attack by the activated proteases.

Because the team combined samples from early through late stage cancer patients, additional work is needed to determine whether either of these fragments would show up in blood before other symptoms of cancer do. If so, those fragments might serve as an early indicator of disease.

The degradome revealed many more differences than full-size proteins did. Looking through the degradome for changes between healthy and diseased samples might also provide new insights for other diseases, Shen said.
-end-
Reference: Yufeng Shen, Nikola Tolić, Tao Liu, Rui Zhao, Brianne O. Petritis, Marina A. Gritsenko, David G. Camp, Ronald; J. Moore, Samuel O. Purvine, Francisco J. Esteva, and Richard D. Smith, Blood Peptidome-Degradome Profile of Breast Cancer, PLoS ONE Oct. 18, 2010, DOI 10.1371/journal.pone.0013133 (http://dx.plos.org/10.1371/journal.pone.0013133).

Pacific Northwest National Laboratory is a Department of Energy Office of Science national laboratory where interdisciplinary teams advance science and technology and deliver solutions to America's most intractable problems in energy, national security and the environment. PNNL employs 4,700 staff, has an annual budget of nearly $1.1 billion, and has been managed by Ohio-based Battelle since the lab's inception in 1965. Follow PNNL on Facebook, LinkedIn and Twitter.

EMSL, the Environmental Molecular Sciences Laboratory located at Pacific Northwest National Laboratory, is a national scientific user facility sponsored by the Department of Energy's Office of Science, Biological and Environmental Research program. EMSL offers an open, collaborative environment for scientific discovery to researchers around the world. EMSL's technical experts and suite of custom and advanced instruments are unmatched. Its integrated computational and experimental capabilities enable researchers to realize fundamental scientific insights and create new technologies. EMSL's Facebook page.

DOE/Pacific Northwest National Laboratory

Related Breast Cancer Articles from Brightsurf:

Oncotarget: IGF2 expression in breast cancer tumors and in breast cancer cells
The Oncotarget authors propose that methylation of DVDMR represents a novel epigenetic biomarker that determines the levels of IGF2 protein expression in breast cancer.

Breast cancer: AI predicts which pre-malignant breast lesions will progress to advanced cancer
New research at Case Western Reserve University in Cleveland, Ohio, could help better determine which patients diagnosed with the pre-malignant breast cancer commonly as stage 0 are likely to progress to invasive breast cancer and therefore might benefit from additional therapy over and above surgery alone.

Partial breast irradiation effective treatment option for low-risk breast cancer
Partial breast irradiation produces similar long-term survival rates and risk for recurrence compared with whole breast irradiation for many women with low-risk, early stage breast cancer, according to new clinical data from a national clinical trial involving researchers from The Ohio State University Comprehensive Cancer Center - Arthur G.

Breast screening linked to 60 per cent lower risk of breast cancer death in first 10 years
Women who take part in breast screening have a significantly greater benefit from treatments than those who are not screened, according to a study of more than 50,000 women.

More clues revealed in link between normal breast changes and invasive breast cancer
A research team, led by investigators from Georgetown Lombardi Comprehensive Cancer Center, details how a natural and dramatic process -- changes in mammary glands to accommodate breastfeeding -- uses a molecular process believed to contribute to survival of pre-malignant breast cells.

Breast tissue tumor suppressor PTEN: A potential Achilles heel for breast cancer cells
A highly collaborative team of researchers at the Medical University of South Carolina and Ohio State University report in Nature Communications that they have identified a novel pathway for connective tissue PTEN in breast cancer cell response to radiotherapy.

Computers equal radiologists in assessing breast density and associated breast cancer risk
Automated breast-density evaluation was just as accurate in predicting women's risk of breast cancer, found and not found by mammography, as subjective evaluation done by radiologists, in a study led by researchers at UC San Francisco and Mayo Clinic.

Blood test can effectively rule out breast cancer, regardless of breast density
A new study published in PLOS ONE demonstrates that Videssa® Breast, a multi-protein biomarker blood test for breast cancer, is unaffected by breast density and can reliably rule out breast cancer in women with both dense and non-dense breast tissue.

Study shows influence of surgeons on likelihood of removal of healthy breast after breast cancer dia
Attending surgeons can have a strong influence on whether a patient undergoes contralateral prophylactic mastectomy after a diagnosis of breast cancer, according to a study published by JAMA Surgery.

Young breast cancer patients undergoing breast conserving surgery see improved prognosis
A new analysis indicates that breast cancer prognoses have improved over time in young women treated with breast conserving surgery.

Read More: Breast Cancer News and Breast Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.