Are you asking about direct phosphorylation of p50/p65 or anywhere upstream of these factors in the TNFalpha signaling pathway?

If I understand your question, then let me explain how this works. NFkB is a transcription factor with 3 subunits. One typical combination of subunits is IkB, p50 and p65, but others exist as well. NFkB is at rest (unactivated) in the cytosol but is activated by the interaction of IKK with the IkB subunit of the NFkB complex. This action requires that IKK phosphorylate IkB. This also results in the degradation of IkB. Once this occurs the p65 and p50 dimer that is left is free to translocate to the nucleus where it initiates gene expression of its gene targets.

With regard to my previous answer please realize that IKK is: I kappa kinase.

Thanks- my question was about the direct phosphorylation of p65 and p50.

The role of IKKs and IkappaB phosphorylation is pretty well known.

On the other hand, there seems to be little hard data on the mechanisms involved in translocating p50/p65 into the nucleus, following IkappaB degradation; hence my query about phosphorylation.

You might check out the PTMs documented at the Human Protein Resource Database

http://www.hprd.org/ptms?hprd_id=01241&isoform_id=01241_1&isoform_name=Isoform_1

http://www.hprd.org/ptms?hprd_id=01238&isoform_id=01238_1&isoform_name=

You'll have to go through the references to see if any of these PTMs have been shown to affect nuclear translocation.

Subhadeep,

Yes. The p65 subunit of NFkb can be phosphorylated by IKK-alpha at Ser536 (Cll Signaling Technology is selling the antibodies). On the other hand, MSK1 also phosphorylates p65 subunit at Ser 276 (this happens in the nucleus probably through an ERK-mediated pathway). There are other upstream kinases that been reported to phosphorylate p65 subunit. I suggest you have a look at the following paper for more information:

Viatour et al. Trends Biochem Sci. 2005 Jan;30(1):43-52.

Phosphorylation of NF-kappaB and IkappaB proteins: implications in cancer and inflammation

http://www.sciencedirect.com/science/article/pii/S0968000404002993

Thanks to Mitra, Daniel and Constantinos for your links. This has been really helpful!