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Cadherins

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Cadherins

Postby Hodag » Tue Dec 15, 2009 10:34 pm

The action of cadherins are, by their nature, calcium-dependent. I have read a lot of articles, but none of them seem to indicate whether the Ca2+ required is intracellular, extracelluar, or a bit of both (I am guessing both).

My question revolves around what happens if you chelate extracellular calcium with EDTA or citrate. Does that inhibit the action of cadherins and, if so, what Ca2+ concentration is the threshold below which the cadherins do not function.

Similarly, if I have two cells attached by a5b1 and a2b1 integrins, which are Ca-independent, they still need to "talk" across the gap junction. If I have chelated all the extracellular calcium, does this inhibit their Ca-dependent signalling across the gap junction?

I am hoping to find a very much below physiological concentration of extracellular Ca that will inhibit the cadherin binding, but will still allow the signal transduction pathway to function, however I am having trouble finding information on threshold Ca concentrations.

If anybody can point me to a few journal articles that discuss threshold requirements for various CAM functions, that would be great!
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Re: Cadherins

Postby MrMistery » Wed Dec 16, 2009 2:01 am

Hodag wrote:The action of cadherins are, by their nature, calcium-dependent. I have read a lot of articles, but none of them seem to indicate whether the Ca2+ required is intracellular, extracelluar, or a bit of both (I am guessing both).


You are guessing wrong. Only extracellular calcium is required. Here's why: http://www.ks.uiuc.edu/Research/cadherin/ Basically without bound calcium the cadherin is not stiff enough.

Hodag wrote:My question revolves around what happens if you chelate extracellular calcium with EDTA or citrate. Does that inhibit the action of cadherins and, if so, what Ca2+ concentration is the threshold below which the cadherins do not function.

Add enough EDTA => cells no longer stick to each other. You can see this effect in cultured cells. The reason is precisely the cadherin adhesion. About the concentration, I donno, but people have surely looked at it when they figured out the Kd for the Ca binding to cadherins. If you know the Kd, you know what concentration to use. Look it up on pubmed.

Hodag wrote: Similarly, if I have two cells attached by a5b1 and a2b1 integrins, which are Ca-independent, they still need to "talk" across the gap junction. If I have chelated all the extracellular calcium, does this inhibit their Ca-dependent signalling across the gap junction?

Not all cells have gap junctions. But if your cells do have gap juctions depleting the extracellular calcium shouldn't harm that, since in the case of a gap junction you basically have the cytoplasm of the two cells connected through a narrow tunnel. So it doesn't matter how much Ca is outside, unless the signaling depends on the extracellular calcium concentration. What i mean is if you have for example two smooth muscle cells: in that case a the spike of Calcium comes mostly from outside the cell, and then it can go through a gap junction to neighboring cells. If you have no Ca outside, then obviously signaling through gap junctions will be impeded. So it all depends on the cell type and the kind of signaling you are interested in studying.

Best,
Andrei
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Re: Cadherins

Postby Hodag » Wed Dec 16, 2009 2:37 am

Andrei,

Thanks for the reply, it is mostly good news. :)

Now I just need to find the concentrations, but PubMed has not been my friend on this one. Normally I live and die by Reference Manager searches but so far nothing helpful. I will have look at the link you provided; perhaps I can go from there.

I think the required concentration I need is between 0.1mM and 0.2mM, but that is somewhat reading between the lines for studies that didn't really address it in this way. Hopefully I can dig some more and find a nice table in a publication.
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