This one's derived from a post I made on my blog and is more or less similar, and is a paper review.
The paper in question is http://www.sciencedirect.com/science/ar ... 0811003564

It is stuck behind a paywall so that is far from ideal, but nonetheless, here goes...

Journal reference - Labelle et al, Direct Signaling between Platelets and Cancer Cells Induces an Epithelial-Mesenchymal-Like Transition and Promotes Metastasis, Cancer Cell. http://www.sciencedirect.com/science/ar ... 0811003564

Abstract

Summary

Interactions of cancer cells with the primary tumor microenvironment are important determinants of cancer progression toward metastasis but it is unknown whether additional prometastatic signals are provided during the intravascular transit to the site of metastasis. Here, we show that platelet-tumor cell interactions are sufficient to prime tumor cells for subsequent metastasis. Platelet-derived TGFβ and direct platelet-tumor cell contacts synergistically activate the TGFβ/Smad and NF-κB pathways in cancer cells, resulting in their transition to an invasive mesenchymal-like phenotype and enhanced metastasis in vivo. Inhibition of NF-κB signaling in cancer cells or ablation of TGFβ1 expression solely in platelets protects against lung metastasis in vivo. Thus, cancer cells rely on platelet-derived signals outside of the primary tumor for efficient metastasis.

Highlights

► Platelet-tumor cell contacts induce a mesenchymal-like metastatic phenotype ► Platelet-derived TGFβ1 is necessary but not sufficient for efficient metastasis ► NF-κB signaling is also necessary but not sufficient and synergizes with TGFβ ► Signals provided outside the primary tumor microenvironment promote metastasis.

The paper is something of a landmark because it has showed how the mere interaction of platelets with cancer cells is sufficient to induce activation of EMT (Epithelial Mesenchymal Transition). It details how the presence of a protein called TGFß derived from platelets, in combination with direct contact between cancer cells and platelets, can activate the NF-kB and Smad signalling pathways that confer invasiveness to cancer cells, thus making metastasis possible.

Just for reference, here is the TGFß followed by the NF-kB pathway.




The main questions the study in the paper addressed were if platelets could stimulate metastasis and if so, by what means and methods. The first question was quite easy to address. They took colon carcinoma cells from a cell line called MC38GFP and breast cancer cells from a cell line called Ep5, they grouped cells from each of those lines into two groups each. One of each group was treated with platelets while the other wasn’t, and the cells were then injected into mice to look for the frequency of metastasis. and bingo, the platelet treated cells showed a higher frequency of metastasis.


Caption - Treatment with Platelets tends to vastly increase the number of metastatic foci compared to untreated cells.

The researchers then examined whether platelet treatment induced an EMT-like phenotype, and they did this by looking at the mRNA and protein concentrations of various genes and their products that are markers of EMT, such as MMP-9 (a matrix metalloproteinase) and found that the expression of such marker genes and proteins is highly upregulated. Some of the markers used were Snail, Vimentin, Fibronectin and PAI-1 for a mesenchymal phenotype, and E-cadherin expression as a marker of epithelial phenotypes (or the loss thereof).



Caption - (D) Relative fold change in mRNA expression in MC38GFP or Ep5 cells treated with buffer or platelets for 40 hr (n = 3). Values are normalized to Gapdh expression. (E) Detection of E-cadherin protein levels by immunoblotting of lysates ofMC38GFPorEp5cells treated as in (D). Amounts of platelets equal to those used to treat cells were also loaded as control (no cells). b-tubulin was used as loading control. (F) Zymography for MMP-9 in the conditioned medium of MC38GFP or Ep5 cells treated as in (D). Amounts of platelets equal to those used to treat cells were also loaded as control (no cells). (G) MC38GFP and Ep5 cells were added at the top of transwells coated with Matrigel and treated with buffer or platelets. The total number of cells that invaded to the bottom of the transwell was counted after 48 hr (n = 3). For (A), (B), (D), and (G) bars represent the mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 were determined by Student’s t test.

The question then would be how platelets could induce EMT, could TGFß be to blame? To find out, they carried out bioinformatics analysis of data from microarray experiments looking for differentially expressed genes when cells were treated with platelets. They found that expression of EMT genes was upregulated and there was increased expression of genes in the TGFß pathway.



Caption - Gene upregulation data from microarray analysis when platelet stimulation is induced. Gene enrichment analysis using Gene Ontology functional categorization is presented in the table. You can see how the upregulated genes are all associated with EMT and with TGF-beta dependent activation processes.

This indicated to them that platelets induced the EMT phenotype through the TGFß pathway. They then wanted to find out if TGFß alone was responsible or if direct contact with platelets also had something to do with said upregulation.

To do this, they set up a rather cute experiment where they used a PAI-1 reporter gene to assay TGFß activation (this is possible because PAI-1 is downstream in that pathway and can be used as a surrogate marker)

They assayed levels of activation when platelets AND TGFß were added as opposed to TGFß alone. They observed more PAI-1 activation in the former than the latter, thus indicating that the presence of platelets and TGFß together act synergistically in activating the pathways involved. The central role of TGFß in the process was confirmed by blocking TGFß using an inhibitory antibody and a small molecule, which led to loss of PAI-1 expression.

The question then, of course, was why the presence of both platelets and TGFß would have more effect in EMT activation compared to TGFß alone. What other pathways would be activated such that the added effect could be accounted for?

To test this, they used reporter based assays for multiple pathways involved in cancer, and found that the releasate from platelets (platelet free) activated the JNK pathway, while the presence of cells and the releasate activated the JNK and NF-kB pathways.

Now this is where things got really interesting. Firstly, they confirmed whether NF-kB was actually able to account for the results of cell-inclusive treatment experiments by using Ep5 cells with mutant NF-kB and a reporter with reference to a control with a normal NF-kB and the corresponding reporter.

They found that mutant cells didn’t show NF-kB activation when treated with platelets, and that these cells had the same metastatic potential as cells that were treated with TGFß alone, thus fully implicating this pathway in platelet contact induced EMT.

These results were further validated when treatment with an NF-kB inhibitor also downregulated the expression of several key markers of EMT, such as MMP-9, in cells with intact NF-kB signalling.

They found that inhibiting cells with the NF-kB inhibitor switched off a reporter in that pathway, but not one in the other pathway, indicating that TGFß activation was independent of NF-kB activation, while the effects were synergistic.

And finally, here’s the piece de resistance of the paper; they showed that blocking TGFß secretion in megakaryocytes and platelets or wrecking the TGFß pathway was enough to prevent metastasis, they did this using mice in which TGFß expression was knocked out where seeding with cancer cells prevented metastasis to the lungs. They also showed that even cells pre-treated with wild type platelets for a while before introduction into TGFß fl/fl mice wasn’t enough to trigger metastasis.

This basically confirms that platelet derived TGFß signalling is absolutely necessary, while NF-kB signalling in synergy with it renders tumour cells potentially more metastatic, but isn’t per se sufficient for metastasis.

They note that this could have therapeutic implications, since TGFß inhibition in platelets doesn’t have physiological effects on normal cells, and if this could be replicated in humans it might serve as a brilliant therapeutic strategy.

However, as always, blocking metastasis, it would appear, would only really be useful in tumours where metastasis hasn’t occurred, how established metastatic disease should be dealt with is still a very open, and problematic question.

Oh, I can really use this in my every day random discussions with people.

Grace wrote:Oh, I can really use this in my every day random discussions with people.

Here's the dummies' guide version if you want it.

Platelets are a kind of blood cell. Cancer is really a problem because tumours tend to metastasize to other parts of the body where they cannot be adequately treated, and left unchecked they kill the patient. Metastasis requires cells to migrate from the original tumour to other parts. Platelets are required for this. Platelets enable cancer cells to do so by inducing what is called a mesenchymal phenotype in originally epithelial cells, which is, surprisingly enough, called an Epithelial-Mesenchymal Transition.

The induction is done through the TGF-beta pathway and the NF-kB pathways. The paper in question details the evidence.

The implications are that blocking platelet derived TGF-beta from inducing EMT could potentially serve as a viable therapeutic strategy to prevent metastasis, thus improving outcomes.



Any more dumbing-down required?

Hey G4L, I read this part:

The paper is something of a landmark because it has showed how the mere interaction of platelets with cancer cells is sufficient to induce activation of EMT (Epithelial Mesenchymal Transition). It details how the presence of a protein called TGFß derived from platelets, in combination with direct contact between cancer cells and platelets, can activate the NF-kB and Smad signalling pathways that confer invasiveness to cancer cells, thus making metastasis possible.

So, if I'm reading this right, ( ) exposure to platelets 'tells' or triggers the process that cancer cells use to "squeeze through" epithelial cells & metastasize?

I wonder if this is evolution at work: cancers need access to blood or lymph vessels to metastasize and 'expand to new territory', so have they evolved a mechanism to 'know' when they've 'made it to the road'?

AlohaChris wrote:Hey G4L, I read this part:

The paper is something of a landmark because it has showed how the mere interaction of platelets with cancer cells is sufficient to induce activation of EMT (Epithelial Mesenchymal Transition). It details how the presence of a protein called TGFß derived from platelets, in combination with direct contact between cancer cells and platelets, can activate the NF-kB and Smad signalling pathways that confer invasiveness to cancer cells, thus making metastasis possible.

So, if I'm reading this right, ( ) exposure to platelets 'tells' or triggers the process that cancer cells use to "squeeze through" epithelial cells & metastasize?

Yes.

AlohaChris wrote:I wonder if this is evolution at work: cancers need access to blood or lymph vessels to metastasize and 'expand to new territory', so have they evolved a mechanism to 'know' when they've 'made it to the road'?

It is evolution at work, yes, but not with any prior intent, it is just that cells which undergo EMT can survive when dissociated from cells and can actively migrate. There might be a selective pressure on cells to metastasize thanks to factors like Hypoxia et cetera in the primary tumour, since tumours are often sites of extensive necrosis and inflammation.

However, metastasis by itself is roughly rather inefficient; it takes loads of cells to produce viable secondary tumours.

EDIT - Fixed open quote tag.

GenesForLife wrote:
Here's the dummies' guide version if you want it.

Ooh, goodie!

The implications are that blocking platelet derived TGF-beta from inducing EMT could potentially serve as a viable therapeutic strategy to prevent metastasis, thus improving outcomes.

Okay, I got that bit.

Now back to this ...

Platelets are a kind of blood cell. Cancer is really a problem because tumours tend to metastasize to other parts of the body where they cannot be adequately treated, and left unchecked they kill the patient. Metastasis requires cells to migrate from the original tumour to other parts. Platelets are required for this. Platelets enable cancer cells to do so by inducing what is called a mesenchymal phenotype in originally epithelial cells, which is, surprisingly enough, called an Epithelial-Mesenchymal Transition.

Any more dumbing-down required?

Now you mention it ... What are "epithelial cells" and what is a "mesenchymal phenotype"? Dummy version please

Epithelial cells are those that comprise the walls of body cavities, bascially, katja.

Mesenchymal cells are basically like embryonic cells in morphology, and have migratory capabilities that epithelial cells lack, which sit anchored to a basement membrane. These cells are derived from the mesenchyme, which is loosely differentiated connective tissue and is derived from the mesoderm. (the mesoderm is one of the three layers of cells in a human embryo, the others being the ectoderm and the endoderm) .

GenesForLife wrote:There might be a selective pressure on cells to metastasize thanks to factors like Hypoxia et cetera in the primary tumour, since tumours are often sites of extensive necrosis and inflammation.

However, metastasis by itself is roughly rather inefficient; it takes loads of cells to produce viable secondary tumours.

Cancers, it seems, are behaving much like single-celled organisms! Bacteria will seek to move away from a hostile environment (hypoxia, necrosis) to a more suitable one with better resources. That's creepy.

A good read, and thanks for the version for dummies made reading the other version easier.. Understanding the process of metastasis is a key to unlocking better treatments, cancers in situ can be cut or burned or poisoned, but not when they spread effectively.

GenesForLife wrote:I wonder if this is evolution at work ...

I wonder how it could be. How would cancers generally, that do not reproduce outside of thier host body, and which die with their host body, evolve over time? Where is the evolutionary pressures to change & survive, to pass on genes? Surely the whole life cycle is lived out in the host, without a chance for adaptation to influence any succeeding generation. Any evolutionary advance within a cancer, ends when the organism dies.

chairman bill wrote:

GenesForLife wrote:I wonder if this is evolution at work ...

I wonder how it could be. How would cancers generally, that do not reproduce outside of thier host body, and which die with their host body, evolve over time? Where is the evolutionary pressures to change & survive, to pass on genes? Surely the whole life cycle is lived out in the host, without a chance for adaptation to influence any succeeding generation. Any evolutionary advance within a cancer, ends when the organism dies.

There are cancers that outlast their host, I had the (hmmm) ? pleasure.. of seeing the now famous dog/wolf sexually transmitted cancer while working in remote northern australia, this cancer is hundreds of years old and still 'alive' in many dogs and dingos in the region. Australia also hosts another infectious cancer that of tasmanian devils which seems to be passed between individuals via territorial or mating fights.

But are the cancers involved in this study, of that type?

Infectious cancer in dogs:

A mysterious contagious cancer which plagues dogs throughout the world may be the first truly transmittable cancer known, a new study suggests.

The cancer cells themselves move directly from dog to dog, acting "parasitically" on each infected animal, the researchers say.

Canine transmissible venereal tumour (CTVT) spreads between dogs through sex or other forms of contact, such as licking and biting, they believe.

The same cancer appears to infect dogs throughout the world and probably originated from a cancer in a single wolf, or a dog closely related to a wolf, which lived between 250 and 1000 years ago, the researchers say.

more here in New Scientist article

GenesForLife wrote:Epithelial cells are those that comprise the walls of body cavities, bascially, katja.

Mesenchymal cells are basically like embryonic cells in morphology, and have migratory capabilities that epithelial cells lack, which sit anchored to a basement membrane. These cells are derived from the mesenchyme, which is loosely differentiated connective tissue and is derived from the mesoderm. (the mesoderm is one of the three layers of cells in a human embryo, the others being the ectoderm and the endoderm) .

Thanks! Yay, I've learned something new

chairman bill wrote:But are the cancers involved in this study, of that type?

I do not think so, but we did not anticipate that cancer cells could live for such long periods and have many hosts, why I brought it up was whether they could evolve and it seems that is possible with some types at least that we have seen them evolve into a 'parasite'.

edit bit of a derail.. sorry.

chairman bill wrote:

GenesForLife wrote:I wonder if this is evolution at work ...

I wonder how it could be. How would cancers generally, that do not reproduce outside of thier host body, and which die with their host body, evolve over time? Where is the evolutionary pressures to change & survive, to pass on genes? Surely the whole life cycle is lived out in the host, without a chance for adaptation to influence any succeeding generation. Any evolutionary advance within a cancer, ends when the organism dies.

I think this refers to somatic evolution of cancer.

Katja is right, we tend to see a shift in allele frequencies in a population of cells in cancer, which is somatic evolution.