Hi. In this video, we're going to be talking about phosphoinositide or phosphoinositol signaling pathways. So this pathway is confusing in the textbook because there seems to be all these different results that happen from them, but it's not very clear on why they're happening or what's activating it, or how all these different things are being activated. So I've tried to divide this into 2 groups, and this is because the phosphoinositide signaling pathway may also be seen as the inositol phospholipid pathway, same thing. Both of these can be activated by the G protein-coupled receptors or the receptor tyrosine kinase, so the enzyme-coupled receptors. So there are 2 main pathways, and they each activate this pathway for different functions. So let's first focus on the GPCR. So how the GPCR is activated is they activate, so once they are activated, the receptors activate this G protein called Gq, and this goes on to activate phospholipase C. Now, phospholipase C is important because when cleavage happens, it results in 2 products. The first is going to be called IP3, and the second is DAG. And if you're interested in what their names, they're listed right there. So IP3 goes on to cause calcium signaling in the cytoplasm, And DAG goes on to activate this protein called protein kinase C, which then goes on to activate a lot of other proteins when calcium is present. So they interact. So the IP3 brings calcium into the cell, and DAG activates proteins that are responsive to calcium. Does all make sense? And so the calcium surge in the cytoplasm triggers a lot of different events, things like egg development, muscle contraction, nerve cell secretion. So calcium is a big signaling molecule, and so this is one of these pathways that the inositol phospholipid pathway leads to the signaling of calcium. So here we have the example. So here, you've probably seen this picture before, but just want to show it to you again. So here you have this lipid, phospholipase C comes in and cleaves it. It forms DAG and IP3. IP3 travels down here and releases calcium, and DAG activates different proteins that are responsive to calcium to then go on and do a lot of different signaling things. Now, on the other hand, RTKs and other types of receptors like cytokine receptors will also activate phospholipase C for a different purpose. But this is still a very similar pathway. So phospholipase C, in this case, will recruit this PI 3-kinase to the membrane, PI 3 kinases. And then once this kinase is here, it can do a lot of things. So, first, it's a kinase, so it's going to add phosphates onto something, and so in this case it's going to add it onto a phosphoinositide lipid. So this is the same lipid that we talked about before. And, once this is phosphorylated, it leads to a bunch of signaling cascades, which can trigger cell division and prevent cell death. It also activates this protein called AKT, which activates a variety of other proteins. And PTEN phosphatase, remember, phosphatases are going to remove phosphates. So, this is how this is actually inactivated, is this PTEN phosphatase. So what this looks like is you have some type of receptor tyrosine kinase. You then get PI 3-kinase activation. You can get AKT activation, which is going to activate a lot of different things. And you can see that there's a ton of different other things that happen down here. You don't need to know these names. But just know these are signaling cascades. They're activating a lot of things. So that's how the RTKs activate the phosphoinositide signaling pathways. So with that, let's move on.
14. Cell Signaling
Phosphoinositide Signaling Pathways
14. Cell Signaling
Phosphoinositide Signaling Pathways - Online Tutor, Practice Problems & Exam Prep
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concept
PI Pathway
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Video transcript
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Problem
ProblemThe inositol signaling pathway can be activated by both GPCRs and RTKs.
A
True
B
False
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Problem
ProblemWhich of the following molecules removes phosphates from PI-3 kinase?
A
Phospholipase C
B
Phosphatidylinositol-3 kinase
C
PTEN Phosphatase
D
Protein Kinase C