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Nuclear Hormone Receptors and Steroid Hormone Signaling

by Kevin Ahern, PhD
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    00:01 So as I noted earlier, not all signaling systems work through membrane receptors.

    00:05 Some examples of those that work internal to the cell - the steroid hormone receptor which works by the process of a steroid hormone diffusing its way across the membrane ultimately to the receptor in the cytoplasm.

    00:17 The thyroid hormone receptor also works in a fashion as I will describe here through the transport system that gets things into the nucleus.

    00:25 Vitamin D has a little bit different route that it gets there.

    00:27 It gets into the cell not through the receptor but through action of a vitamin D transport protein that grabs the vitamin D and the cell membrane and then transports it to the receptor in the cytoplasm, where that then takes the vitamin D into the nucleus to exert its effects.

    00:42 And at last the retinoic acid/retinoid receptor has a transport system that also gets retinoic acid ultimately into the nucleus for controlling gene expression.

    00:50 Each of these nuclear hormone receptors is depicted schematically here.

    00:55 They have an N-terminal region that’s shown on the left and a C-terminal region that’s shown on the right.

    01:00 And that N-terminal region has a DNA binding domain that is specific to binding a specific sequence within a DNA molecule.

    01:09 Another part of the protein has a ligand binding domain, that’s the part that binds to the receptor hormone.

    01:16 It is the binding of that receptor hormone that causes the overall receptor to exert the control on gene expression that it controls.

    01:23 So these receptor hormones bind to specific sequences in DNA molecules as I said, that are known as hormone response elements that occur in the DNA.

    01:33 And these are specific for each of the individual transcription factors that I’ve described here.

    01:38 Now nuclear hormone signaling helps to control processes of metabolism, inflammation, immune function, water and salt balance, sexual characteristics and response to illness and injury.

    01:50 That’s a pretty wide variety of things that’s needed for a body to be able to respond to.

    01:55 Steroid signaling uses intracellular non-membrane receptors as I’ve noted.

    02:00 There are five classes of steroid receptors that are broken down into two groups - the corticosteroids and the sex hormones.

    02:08 Signaling mostly affects the gene expression so it tends to be much slower in its effects than those processes that affect enzyme activities.

    02:18 So let’s look at the process of steroid signaling going on in the cell.

    02:22 Steroid hormone is released into the blood, that’s the first messenger.

    02:25 And it travels to its target.

    02:27 At its target it crosses the lipid bilayer of the target cell without interaction of other proteins.

    02:33 Inside the cytoplasm it binds to an internal receptor.

    02:36 And that internal receptor has its shape changed as a result of binding of the hormone.

    02:42 This converts the receptor into what’s known as a transcription factor.

    02:47 The transcription factor goes into the nucleus and binds to the hormone response element in the DNA, affecting its transcription.

    02:55 So the movement of the transcription factor into the nucleus with the hormone bound to it causes a different set of genes to be made than was being made before the receptor protein went into the nucleus.

    03:07 So this is shown schematically in the figure I’m showing you here.

    03:10 We see for example a cell, shown as a rectangle in grey.

    03:15 We see inside of it, a receptor protein that’s bound to another molecule and we see the nucleus.

    03:21 So here’s the phospholipid bilayer that surrounds that cell.

    03:24 And there is the receptor bound to a protein known as Hsp70.

    03:29 Now Hsp stands for heat shock protein 70.

    03:32 And heat shock proteins have quite a variety of functions, but one of the functions the heat shock protein 70 has here is that it’s preventing the receptor protein from going into the nucleus.

    03:43 It’s keeping it in the cytoplasm.

    03:45 Well here’s the steroid hormone that arrives in the blood, it crosses the lipid bilayer on its own, it interacts with the receptor protein.

    03:54 And binding of the hormone to the receptor protein causes the receptor protein to let go of Hsp70.

    04:02 Well since Hsp70 was what was keeping the protein from going into the nucleus, the protein that is the receptor carrying the steroid hormone now moves into the nucleus and goes and activates transcription of genes that have hormone response elements that are linked to them.

    04:18 In this way, the gene expression of the cell has been changed.


    About the Lecture

    The lecture Nuclear Hormone Receptors and Steroid Hormone Signaling by Kevin Ahern, PhD is from the course Hormones and Signal Transduction. It contains the following chapters:

    • Nuclear Hormone Receptors
    • Steroid Hormone Signaling
    • Steroid Hormone Signaling

    Included Quiz Questions

    1. None of the answers are true.
    2. All of the answers are true.
    3. They transmit signals through the lipid bilayer.
    4. They are protein kinases.
    5. They act more rapidly than GPCRs.
    1. All of the answers are true.
    2. None of the answers are true.
    3. They cause steroid hormone receptors to release heat shock proteins.
    4. They cause the steroid hormone receptor to carry them to the nucleus.
    5. They stimulate transcriptional activity of their receptors.

    Author of lecture Nuclear Hormone Receptors and Steroid Hormone Signaling

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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