One small molecule that regulate gene expression plays a big role in keeping human safe from the machinations of cancer. In human lung cancer cells, low levels of the microRNA, miR-125a-5p, which enables the death of aberrant cells like cancer cells, correlates with high levels of the protein TIMP-1, which is already associated with a poor prognosis in patients with cancer.
Conversely, when they decrease TIMP-1 levels in these highly lethal cancer cells, tumor spread goes down while rates of cell death go up along with expression of miR-125a-5p, says Dr. Mumtaz V. Rojiani, cancer biologist in the Department of Medicine at the Medical College of Georgia and a member of the Molecular Oncology and Biomarkers Program at the Georgia Cancer Center at Augusta University.
While increasing microRNA levels is technically difficult, further delineating how cancer hijacks these normal body systems may help identify new treatment targets. TIMP-1 has a positive role in a healthy body to balance levels of enzymes the body makes to ease cell movement for things like wound healing or reproduction.
The healthy body and cancer make these enzymes, matrix metalloproteinases, or MMPs, to break down the surrounding matrix that helps keep cells stable. While it's critical to positives like wound healing, when the matrix breakdown is usurped by cancer, it also gives cancer cells this freedom to move.
In cancer, TIMP-1 levels rise dramatically and it has a distinctive role enabling both growth of new blood vessels and inhibition of apoptosis, a cell's natural inclination to die if something unfixable is wrong. In cancer, what the tumor cells do is start secreting a lot more of these enzymes so they can break down the matrix and start migrating and metastasizing.
Classically, TIMP-1 should be inhibiting MMPs but over the years it has been found to have other functions that actually increase tumor aggressiveness. In their studies of TIMP-1 expression in human lung cancer cells, they saw this aggressive response. It turned out that TIMP-1 is like a two-faced individual smiling at cancer sometimes and other times cutting it off.
Increased levels of two-faced TIMP-1 have been found in increased tumor spread and poor prognosis in breast, gastric and colorectal cancers as well as the non-small cell lung cancer the MCG scientists studied, which accounts for about 85 percent of all lung cancers and has a five-year survival rate of under 20 percent.
TIMP-1 overexpression also is associated with increased upregulation of Bcl-2, a protein which can prevent apoptosis, or cell death. To make bad matters worse, a key way chemotherapy works is by inducing apoptosis and TIMP-1 has been associated with potentially deadly drug resistance.
However, with high expression of miR-125a-5p, TIMP-1 becomes the target. One result is increased expression of the gene p53, a known tumor suppressor, which enables cell death.
When ressearchers knocked down TIMP-1 expression, it significantly increased expression of miR-125a-5p. Conversely, when they restored higher levels of TIMP-1, miR-125a-5p expression went down. The look of the cancer cells changed with the level of TIMP-1. At high levels they looked more like cells unshackled from their current location and able to migrate and invade. When they decreased TIMP-1 levels, the cells pretty much stayed put.
Adding more synthetic miR-125a-5p to the cancer cells, and the lung cancer cells moved more toward a stationary normal look and cell death increased. When they inhibited miR-125a-5p, the cells were ready to roam. Looking at the biopsies of lung cancer patients, they found as expected TIMP-1 expression much higher in the lung cancer tissue than nearby healthy tissue. But they also saw an inverse relationship between high levels of TIMP-1 and miR-125a-5p levels. In fact, tumor cells had almost no miR-125a-5p.
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