How does Protein Kinase get inside the nucleus?

[BlondeCookie]

Quick question. How does Protein Kinase get inside the nucleus? Via the pores? Via diffusion?

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[el.harpo]

Quick question. How does Protein Kinase get inside the nucleus? Via the pores? Via diffusion?

I dont think it could diffuse across a double membrane (with a hydrophobic interior) being a cytoplasmic (hydrophilic) enzyme. Other than that the only major mechanism of transport that we learned for the nucleus was through nuclear pores. So, if I had to guess, I would say it crossed the membrane through the nuclear pores.

 

[NilamPatel]

correct me if i am wrong but don't protein kinases phosphorylize other proteins and most use a cascade system or 2nd messanger to do so?

 

[BlondeCookie]

I dont think it could diffuse across a double membrane (with a hydrophobic interior) being a cytoplasmic (hydrophilic) enzyme. Other than that the only major mechanism of transport that we learned for the nucleus was through nuclear pores. So, if I had to guess, I would say it crossed the membrane through the nuclear pores.

The nucleus has a double membrane?! I forgot about that! Thanks for the reminder. Does anything diffuse across the nuclear membrane or any double membrane organelle for that matter? Speaking of which, the only other double membrane organelle is the mitochondria. Correct???

Nilam, yes you are right. Protein kinases also function in a G-protein/cAMP 2nd messenger pathway in which the protein kinases phosphorylate many other protein kinases.

 

[strangelight]

correct me if i am wrong but don't protein kinases phosphorylize other proteins and most use a cascade system or 2nd messanger to do so?

Yeah, that's what I was thinking too...

 

[NilamPatel]

i believe steroid hormones are lipid soluable (hydrophobic) so they cross membranes and change transcription...

 

[sweetstuff25]

I thot protein kinases only work in the cytoplasm? why do they need to go to the nucleus? lipid soluble molecules are the ones that affect transcriptional activity by going to the nucleus.

 

[BlondeCookie]

I thot protein kinases only work in the cytoplasm? why do they need to go to the nucleus? lipid soluble molecules are the ones that affect transcriptional activity by going to the nucleus.

OK everybody. There are two pathways in which protein kinases work.
1) In the cytoplasm: g-protein linked receptor/cAMP second messenger pathway. You know, the one where cAMP activates the 1st protein kinase, which in turn, activates the 2nd protein kinase, and then 3rd, 4th, etc.. Then, you get your enhanced cellular response for this pathway.

2) In the nucleus: protein kinase goes from the cytoplasm to the nucleus and modulates activity of transcription by binding to transcription factors. The altered gene expression is the cellular response for this pathway.

Holy cow! I just wanted to know how the protein kinases got inside the nucleus! Is it via the pores? Or via diffusion? And about steroids. Yeah, they can diffuse across the cell's plasma membrane easily because it's not a double membrane like the nucleus. So, how about that? Do you think that steroids can diffuse across the double membrane of the nucleus???

 

[totalcommand]

The proteins (like protein kinases) pass through the nuclear pores. Oftentimes, phosphorylation of the protein kinase itself is the signal to move the protein either in or out of the nucleus.

Protein kinases are sometimes involved in the 2nd messenger system, but that doesn't mean they have to be in the cytoplasm.

For example, CDK's, which control the cell cycle, often phosphorylate proteins in the nucleus that will allow DNA replication or growth to occur (RB is phosphorylated, releasing E2F, which allows entry into S phase from G1).

 

[riceman04]

The nucleus has a double membrane?! I forgot about that! Thanks for the reminder. Does anything diffuse across the nuclear membrane or any double membrane organelle for that matter? Speaking of which, the only other double membrane organelle is the mitochondria. Correct???

Nilam, yes you are right. Protein kinases also function in a G-protein/cAMP 2nd messenger pathway in which the protein kinases phosphorylate many other protein kinases.

recall that if something has a Nuclear Localization Sequence on it then it is allowed to enter the member if over 70 Kilo daltons (think)

 

[NilamPatel]

we have officially exhausted this thread

 

[TIGIBedHead]

Ok, so the two pathways you described are really parts of the same pathway. This is way beyond the scope of the MCAT, but cAMP activates PKA, which phosphorylates pre-existing enzymes that stimulate breakdown of glycogen into glucose, and inhibit glycogen production. This part of the pathway is responsible for the rapid effects of adrenaline (and is the enhanced cellular response you referred to).

The slower acting effects of adrenaline are directed by PKA phosphorylation of CREB, which is a transcriptional activator. So it is not the protein kinase, but rather its substrate, that crosses the lipid bilayer of the nucleus.

The only molecules that can pass the lipid bilayer into the nucleus are lipid soluble molecules, which include steroids. They diffuse through the pores of the nuclear membrane.