January 22 2008 post. A blog reader and I recently had an interesting exchange about this transcription factor, which is so important in myeloma…in a negative sense, unfortunately. Our discussion gave me the incentive to read more about it. My good friend Sherlock (grazie!) sent me a study published in January (2008) in “Experimental Biology and Medicine,” titled “Nuclear Factor-kB Activation: From Bench to Bedside,” and co-authored by Prof. B. Aggarwal (abstract: http://tinyurl.com/2m6j2g).
This transcription factor, discovered in 1986, was called NF-kB “because it was found in the nucleus bound to an enhancer element of the immunoglobulin kappa light chain gene in B cells.” Okay, wrap your brain around that! But seriously, if you reread the quote slowly, it begins to make sense: it’s a thingie (protein complex or transcription factor) sticking to the “kappa” gene inside a B cell’s nucleus.
Under normal circumstances, our immune system needs NF-kB to fight off diseases and infections. And until it is needed, this transcription factor follows my cats’ example and takes a lot of very long naps. I don’t want to go into its mechanisms of action (complicated stuff!), at least not today. Let it suffice that, once it has accomplished its task, it settles back down for another nap.
The study informs us that NF-kB is present in every type of cell, not just B cells as was first thought. Researchers have in fact discovered that it is located in the cytoplasm (the watery environment surrounding the cell nucleus) of all types of animal (from the fruit fly to us) cells. Another important finding is that it moves, or translocates, to the cell nucleus only when activated. Otherwise, it stays in, or (once it has finished its task) goes back to, the cytoplasm.
Things change with cancer. That’s when NF-kB turns into Mr. Hyde: it goes bonkers for a variety of reasons and ends up being active ALL the time, or constitutively active. And when this happens, NF-kB remains inside the cell nucleus, that is, it doesn’t return to the cytoplasm. No more naptime!
Skipping the technical parts about heterodimers, polyubiquitination and nuclear localization sequences (!), let me get to what we are really interested in: how does this transcription factor get activated in cancer cells? The study provides an answer: “NF-kB is activated by many divergent stimuli, including proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), epidermal growth factor (EGF), T- and B-cell mitogens, bacteria and lipopolysaccharides (LPS), viruses, viral proteins, double-stranded RNA, and physical and chemical stresses.” Radiation and chemotherapy also activate NF-kB. Speaking of which, the study tells us also that "Cells that express constitutively activated NF-kB are resistant to various chemotherapeutic agents and radiation treatment.” Vicious circle?
Another key sentence: “In tumor cells, different types of molecular alterations may result in impaired regulation of NF-kB activation. In such cases, NF-kB loses its transient nature of activation and becomes constitutively activated. This leads to deregulated expression of NF-kB– controlled genes.” NF-kB, the study continues, plays a critical role in cancer cell survival, inflammation, growth and so on. It regulates genes that are implicated in cancer cell proliferation, including TNF-alpha, IL-6, to name just a couple that we know are essential growth factors in multiple myeloma. It also regulates some of the cell cycle-regulatory proteins such as cyclin D1, also involved in myeloma (see my page on Ursolic Acid or my December 4 2007 post for more info on this gene, which has recently been associated with disease activity and progression).
Activated NF-kB is also implicated in the control of anti-apoptotic genes, that is, genes that keep cancer cells healthy and alive, such as survivin and Bcl-2 (again, see my post on ursolic acid). Furthermore, it regulates matrix metalloproteinases, or MMPs, which are proteases (protein-dissolving enzymes) that, among other things, promote cancer cell growth and angiogenesis. Okay, so there is no question that constitutively active NF-kB is not a good thing.
That’s enough for today, but I would like to end with a question: if we systemically inhibit NF-kB in order to stop our cancer from progressing, doesn’t that leave us more susceptible to infections? (More on this topic SOON!)
February 2 2008 post ("the dual nature of NF-kB): This is the continuation of my January 22 post. From the Aggarwal (et al) NF-kB study, we know that when NF-kB “is found to persist in the nucleus, it is referred to as constitutive activation. […] The precise role of constitutive activation in tumors is not known but has been linked to resistance to apoptosis in human cutaneous T-cell lymphoma cells. It is tempting to believe that a similar mechanism accounts for the progression of all tumors that constitutively express NF-kB, but such a link has yet to be clearly identified.”
This entire section is interesting, actually, since it reports that another thing that has not been identified is the actual stimulus that renders NF-kB active all the time. What is clear, though, is that “Cells that express constitutively activated NF-kB are resistant to various chemotherapeutic agents and radiation treatment.”
And read this. In renal cell carcinoma (RCC) patients, “Serum C-reactive protein (CRP) elevation correlated with the increase in NF-kB activation; therefore, NF-kB may be a cause of the inflammatory paraneoplastic syndrome.” As we Myeloma Club members know, CRP reflects IL-6 activity and is thus an important marker for us. (My CRP, by the way, is within the normal range.) At any rate, I thought it interesting that this study reports a connection between high CRP and NF-kB. Well, well.
Another interesting quote: “Another virus that contributes to human cancer via NF-kB is the Epstein-Barr virus (EBV) implicated in Burkitt’s and Hodgkin’s lymphomas. The EBV nuclear antigen (EBNA)-2 and latent membrane protein (LMP)-1 enhance NF-kB activity thereby preventing apoptosis in EBV-transformed B cells.” While I was in grad school in Toronto, I tested positive for EBV. I was quite ill for about a month, tired all the time, etc., as I recall. Anyway, coincidentally (or…not?), a few years later I was diagnosed with MGUS. Well, I suppose it’s pointless to speculate, but this is not the first time I have read about the EBV-cancer link. Let’s proceed.
I found a fascinating study online (full study: http://tinyurl.com/2ntng6) titled “Good cop, bad cop: the different faces of NF-kB” that appeared in the January 2006 issue of “Cell Death and Differentiation.” It examines the different functions of this transcription factor, including that (drum roll!) of TUMOUR SUPPRESSOR. No kidding. NF-kB can promote both tumour growth and tumour suppression. Bad cop, good cop. How about that?
It is in this study that I read that NF-kB can be triggered by hundreds of “activators.” Hundreds? Parts of this study are barely intelligible, but I did manage to grasp a few basic concepts. The “classical” or “canonical” NF-kB pathway occurs when this transcription factor translocates, or moves, from the cytoplasm to the nucleus. This is when NF-kB gets activated by inflammatory cytokines such as tumour necrosis factor (TNF)-alpha and IL-1, in response, say, to a bacterial infection. The rest of that particular paragraph is not meant for non-scientific brains, for sure. So, skip, skip, skip! What matters is that at the end of this complicated process of activation, NF-kB ends up in the cell’s nucleus. This can occur in a matter of minutes. Amazing, eh? Then, once it has performed its good cop duties, under normal circumstances, NF-kB is escorted back (by a gene called IKB-alpha) to the cytoplasm, a process I mentioned briefly in my earlier post.
Then we have the “noncanonical” or “alternative” NF-kB pathway, which is activated by other kinases and, for instance, chemotherapy drugs. Some stimuli, such as UV-C (Short-wave ultraviolet radiation), activate NF-kB both by IKK-dependent and IKK-independent pathways. Ok, ok, my eyes are glazing over, too, and besides, I don’t want to get into too many details. Let’s stay focused on the main points.
Under certain conditions and in response to certain types of stimuli, it would appear that NF-kB can have proapoptotic effects. This “is consistent with the hypothesis that it is the mechanism of induction of NF-kB that determines its physiological function.” It’s all a matter of context, in other words. The important thing is that “If differences in the NF-kB response to a chemotherapeutic drug also occur in different tumors in patients or between patients with apparently the same type of cancer, the ability to more accurately diagnose NF-kB status could profoundly affect treatment choice and outcome.” (Apart from that unfortunate split infinitive, this is quite an interesting statement.)
We already know that NF-kB has pro-inflammatory effects. But the study shows that “NF-kB activity can also be required for the resolution of an inflammatory response. NF-kB activity in the later stages of inflammation has been associated with induction of anti-inflammatory genes and the induction of cell death. Moreover, inhibition of this late-stage NF-kB activity extended the length of the inflammatory response, inhibited the expression of p53 and Bax, and prevented apoptosis.” So sometimes NF-kB can reduce inflammation. I am not sure what late-stage NF-kB activity means, but the inhibition of the tumour-suppressing p53 gene is certainly not a good thing. More research needed.
Now read this shocker: “Because NF-B can perform a tumor suppressor function in some tissues, will its inhibition actually promote cancer in some situations?” Ouch!
The answer is: probably not, since treatment is “relatively short term,” and thus its inhibition of NF-kB would not have enough time to give rise to cancer. So the inhibition of NF-kB, the study states, seems to be the best approach to treating cancer. If the treatment were long-term, though, such as in the treatment of chronic inflammatory diseases, the “continuous suppression of NF-kB activity over a number of years could manifest itself in, for example, squamous cell carcinoma.”
This is a real head-scratcher. A "damned if you do, damned if you don’t" situation. I’d better stop here before my brain melts. But I have not finished with this topic. Not at all.