Posts Tagged ‘gene’

Circulating tumor cell clusters more likely to cause metastasis than single cells

“While CTCs are considered to be precursors of metastasis, the significance of CTC clusters, which are readily detected using devices developed here at MGH, has remained elusive,” says Shyamala Maheswaran, PhD, of the MGH Cancer Center, co-senior author of the Cell paper. “Our findings that the presence of CTC clusters in the blood of cancer patients is associated with poor prognosis may identify a novel and potentially targetable step in the blood-borne spread of cancer.”

In their experiments the team used two versions of a microfluidic device called the CTC-Chip — both developed at the MGH Center for Engineering in Medicine — that captures CTCs from blood samples in ways that make the cells accessible for scientific testing. One version — the HBCTC-Chip — can efficiently capture extremely rare CTCs in a blood sample. Another version, the CTC-iChip, rapidly isolates CTCs in a way that does not rely on preidentified tumor antigens, allowing capture of cells with gene expression patterns that may be missed by the antibodies used in the HBCTC-Chip.

A series of experiments in animal models of breast cancer revealed that:

  • CTC clusters are made up of cells that probably were adjacent to each other in the primary tumor, not cells that proliferated after entering the bloodstream.
  • Although CTC clusters make up only 2 to 5 percent of all CTCs, they contributed to around half of lung metastases resulting from implanted breast tumors, indicating a metastatic potential 23 to 50 times greater than single CTCs.
  • CTC clusters injected into mice survived in greater numbers than did single CTCs, and metastases developing from clusters led to significantly reduced survival.
  • CTC clusters disappear from the animals’ bloodstreams more rapidly than do single CTCs, probably because they become lodged in capillaries where they give rise to metastases.

Analysis of blood samples taken at several points in time from a group of patients with different forms of advanced metastatic breast cancer found CTC clusters in the blood of 35 percent of patients and that the survival of those with more clusters in their blood was significantly reduced. Similar analysis of samples from a group of prostate cancer patients also found an association between the presence of CTC clusters and dramatically reduced survival.

RNA sequencing of both single and clustered CTCs from breast cancer patients identified several genes expressed at elevated levels in CTC clusters, one of which — a protein called plakoglobin — also was overexpressed in the primary tumors of patients with reduced survival. Analysis of blood and tissue samples from one patient revealed that plakoglobin was expressed in CTC clusters but not single CTCs and also was expressed in some portions of both the primary tumor and metastases. Plakoglobin is a component of two important structures involved in cell-to-cell adhesion, and the investigators found that suppressing its expression caused CTC clusters to fall apart, reducing their metastatic potential, and also disrupted cell-to-cell contact between breast cancer cells but not normal breast tissue.

“It is possible that therapeutically targeting plakoglobin or pathways involved in cell-to-cell adhesion within cancer cells could be clinically useful, especially in patients in whom CTC clusters are found,” says Nicola Aceto, PhD, of the MGH Cancer Center and lead author of the Cell paper. “We need to investigate that possibility along with determining whether further characterization of both single CTCs and CTC clusters will provide further insight into differences in their biology, drug responsiveness and their contribution to the process of metastasis.”

source : http://www.sciencedaily.com/releases/2014/08/140828135519.htm

How premalignant cells can sense oncogenesis, halt growth

Since the 1980s, scientists have known that mutations in a human gene called RAS are capable of setting cells on a path to cancer. Today, a team at Cold Spring Harbor Laboratory (CSHL) publishes experiments showing how cells can respond to an activated RAS gene by entering a quiescent state, called senescence.

CSHL Professor Nicholas Tonks and Benoit Boivin, now a University of Montreal Assistant Professor, co-led a team that traced the process in exquisite detail. They began by confirming that activation of mutant, oncogenic H-RAS, one of the human RAS oncogene variants, spurs cells to generate hydrogen peroxide (H2O2), a form of reactive oxygen species, or ROS. “Most people, when they think about ROS, think about the great damage they can do at high concentrations,” says Tonks. “But this research exemplifies how the controlled production of ROS in cells can play a beneficial role.”

The team showed how the production of ROS in response to oncogenic H-RAS enables cells to fine-tune signaling pathways, leading them to enter a senescent state. A key part of this process is the impact of ROS on a protein called PTP1B. Tonks discovered PTP1B some 25 years ago. It is an enzyme — one in a family of protein tyrosine phosphatases (PTPs), of which there are 105 in humans — that performs the essential biochemical task of removing phosphate groups from amino acids called tyrosines in other proteins. Adding and removing phosphates is one of the principal means by which signals are sent among proteins.

In cells with oncogenic H-RAS, ROS is produced in small quantities, sufficient to render PTP1B inactive. The team found that with the phosphate-removing enzyme unable to do its usual job, a key protein called AGO2 remains phosphorylated — with the consequence that it can no longer do what it normally does, which is engage the cell’s RNA interference machinery. In normal cells, the RNAi machinery represses a gene called p21. But in this specific condition — with H-RAS oncogenically activated, PTP1B inactivated by ROS, and RNAi disabled — p21 proteins begin to accumulate unnaturally, the team discovered.

“This is the key step — accumulation of p21 proteins effectively halts the cell cycle and enables the cell to enter the senescent state,” explains Ming Yang, a doctoral student in the Tonks lab. She and Astrid Haase, Ph.D., a postdoctoral investigator in the laboratory of CSHL Professor Greg Hannon, are the first two authors, respectively, on the team’s paper, published in Molecular Cell.

“This is confirmation of a hypothesis we presented five years ago,” Tonks says. “We knew that oncogenic RAS induced the production of ROS. We proposed that this would lead to regulation of PTPs, and using the example of PTP1B this is precisely what the team discovered in this work — showing also how inactivation of this PTP is part of a complex signaling cascade that can culminate in the induction of senescence.”

ROS have been linked to the pathogenesis of several diseases including Alzheimer’s, diabetes and heart failure. “By showing that PTP1B inactivation by oxidation prevents AGO2 from doing its job, we make a clear link between ROS and gene silencing which could also be observed in other pathologies” says Boivin. Hence, the role of PTP1B in keeping the RNAi machinery active could have important ramifications.

Entering senescence is not enough to arrest oncogenesis completely. Oncogenic mutations typically multiply as cancers evolve to promote their survival and proliferation. But the current work does show the potential importance of knowing the genetic background of a cancer patient, for there are windows of time — narrow though they may be — in which naturally occurring processes induce pauses in growth.

source : http://www.sciencedaily.com/releases/2014/08/140828135521.htm

RNA sequence could help doctors to tailor unique prostate cancer treatment programs

Colin Collins and Alexander Wyatt, and other researchers from the Vancouver Prostate Centre at the Vancouver Coastal Health Research Institute, matched 25 patients’ treatment outcomes with the RNA sequence of their prostate cancer tumors. They suggest that similarities between the RNA of some of the patients’ tumors could open up new avenues of treatment.

Prostate cancer is the fourth most common cancer worldwide, but can be effectively managed. Doctors normally recommend a combination of therapies, because patients’ reaction to treatment varies considerably. The side-effects of these treatments can be significant, so current research is focused around precision medicine — classifying patients on their tumor’s molecular changes, and only giving them the treatments that are expected to be most effective.

To investigate variations between the highest risk cases of prostate cancer, researchers conducted a range of genomic analyses, including sequencing the RNA in 25 patients’ prostate tumors. The RNA molecules direct which proteins the cell produces, so the RNA sequences show how tumor cells behave differently to normal cells.

Alexander Wyatt, Vancouver Prostate Centre, says: “Most genomic sequencing studies have focused on the DNA, which gives us important information about a tumor’s history. In our study we examined RNA, which tells us which genes are being used and are disrupted at the time the tumor was collected.”

They then matched up this data with the detailed follow-up information that they had for each of the patients. They were then able to see what sequence disruptions were associated with a positive reaction to different therapies, and they believe this could aid personalized medicine.

Alexander Wyatt says: “We were surprised by the sheer number of genomic differences between patients. This complexity may help explain why patients respond differently to treatment, and why some tumors grow faster than others. The more we understand tumor-to-tumor variability, the closer we come to accurately tailoring a patient’s management specifically for his own tumor. Overall, this is a very exciting time for cancer research, as global sequencing efforts mean we are advancing towards precision oncology.”

Another potential use of this information is that in certain groups, there was a similarity in the type of genes and pathways that were disrupted in the tumors. This might indicate an underlying cancer mechanism that could be exploited to create new cancer treatments.

Alexander Wyatt says: “Despite the enormous complexity between patients at the individual gene level, when we examined the functions of affected genes, clear commonalities between groups of patients emerged. Ultimately it may be possible to exploit this convergent biology.”

source : http://www.sciencedaily.com/releases/2014/08/140826091051.htm