The application of Proteomics to BHD research?

Genomic and clinical studies make up the majority of published research into BHD Syndrome. Proteomics is the large scale analysis of proteins (or the ‘proteome’) and can be used to identify differential transcription of proteins and their biological activity. There are currently no proteomic based studies being performed in the field of BHD research.Would its implementation help further our knowledge of the disease and support ongoing studies? A Chinese group based at the Beijing Proteome Research Centre, China have used proteomic analysis to provide comprehensive functional annotation of proteins implicated in liver development and disease (Sun et al, 2010), could a similar project be used to identify the ins and outs of the BHD kidney?

Sun A et al, 2010. Liverbase: a comprehensive view of human liver biology. J Proteome Res. Jan;9(1):50-8.

Overlap between TAZ and FLCN?

Makita et al, 2008 determined that TAZ is essential for developmental mechanisms involved in renal and pulmonary organogenesis and that its dysfunction may be a pathogenic mechanism in common human disease. Inactivation of TAZ in mice resulted in pathological changes in the kidney and lung that resemble the common human diseases polycystic kidney disease and pulmonary emphysema. After birth, only one-fifth of TAZ-deficient homozygotes grew to adulthood and demonstrated multicystic kidneys with severe urinary concentrating defects and polyuria. Furthermore, adult TAZ-deficient homozygotes exhibited diffuse emphysematous changes in the lung.

TAZ, a transcriptional co-activator with a PDZ-binding motif (also called WWTR1) is a 14-3-3-binding molecule. TAZ acts as a co-activator for several transcription factors as well as a modulator of membrane-associated PDZ domain-containing proteins, but its physiological roles remain unknown.

The coexistence of renal and pulmonary defects observed in TAZ-deficient mice hasn’t been observed before. TAZ may have a role in a pathway common to pulmonary and renal development and so further investigation could uncover a common mechanism for organogenesis and pathogenesis of human diseases. That said, is this phenotype limited to a single mouse model and due to the specific genetic background or could the similarities observed between this phenotype and BHD Syndrome suggest any mechanistic overlap between TAZ and FLCN?

Makita R et al, 2008. Multiple renal cysts, urinary concentration defects, and pulmonary emphysematous changes in mice lacking TAZ. Am J Physiol Renal Physiol. Mar; 294(3):F542-53.

How do you say ‘Birt-Hogg-Dube’ in French?

Eagle eyed visitors will by now have seen that we are currently utilising the Google Translate service to translate into several languages. At the moment, the site can be converted into French, Spanish, Dutch, German, Greek, Chinese and Japanese by clicking on the respective flag on the home page.

The site will open up in a new window and can be navigated in its entirety in the translated language. Because we are using a third party application we aren’t responsible for quality of the translated sites but welcome your feedback on the quality of the translations and suggestions for other languages. We hope that this function will allow us to appeal to a broader audience.

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Hong et al, 2010: What it tells us about Folliculin…

Last week I blogged about a newly published article in the journal Molecular Cancer (link). In it, the authors compared the growth (in vitro and in vivo) of a cell line containing a series of  wildtype or mutant FLCN transgenes; determining that wildtype FLCN suppressed xenograft tumour growth in vivo.

Gene expression profiling also showed that specific genes involved in angiogenesis, cadherin signalling and TGFβ signalling were differentially expressed in null or mutant FLCN expressing cell lines, compared to the wildtype. FLCN’s role in TGFβ signalling is the focus for the rest of the paper, rightfully so given the gravitas of TGFβ signalling in tumourigenesis. I also wonder whether the deregulation of angiogenesis and cadherin signalling are secondary adaptive measures that support tumourigenesis, or whether they occur downstream of the deregulation of TGFβ signalling in these tumours (or even both).

However, what I find particularly interesting is that when the authors examined how FLCN caused deregulation of TGFβ signalling, they showed that the phosphorylation status of downstream SMADs was unaffected by mutant FLCN, but that several downstream targets of TGFβ were, suggesting a role for FLCN in SMAD-independent TGFβ signalling. Whilst this finding is very exciting as it potentially places FLCN within a very specific signalling niche (potentially making it easier to examine), it may also prove to be a double edged sword since non-SMAD TGFβ signalling isn’t fully explored in itself, albeit because the SMADs themselves are so ubiquitous within the cell they’re a feature that can’t be ignored!

Paper Profile: Hong et al, 2010

One of the biggest challenges currently facing BHD researchers is elucidating the role of FLCN’s within the cell. There’s no real way of fixing something unless you know how everything should normally fit into place, whether it be a bike, a car or even a human!

A new article in the journal Molecular Cancer, by Seung-Beom Hong et al1 for me, is something to get quite excited about and I think that a lot of future research will look to this as it’s starting point.

Using an elegant combination of in vitro cell based assays, in vitro xenograft studies and gene expression profiles, the authors have successfully demonstrated that FLCN has an essential role in the regulation of components of TGF-β signalling and indeed confirm their deregulation in BHD-associated kidney tumours. This is a great step forward in understanding pathogenic mechanism underlying BHD syndrome and as such, throws up many new avenues for research that I’m sure will be followed up.

Regular readers will know that I usually dissect published information and try to look for synergy with other work in the area, and I’ll be doing so with all the data that this paper has generated in due course – I just thought I’d give everyone a heads up about its publication and why it’s so exciting.

1. Hong SB, Oh H, Valera VA, Stull J, Ngo DT, Baba M, Merino MJ, Linehan WM, Schmidt LS. Tumor suppressor FLCN inhibits tumorigenesis of a FLCN-null renal cancer cell line and regulates expression of key molecules in TGF-beta signaling. Mol Cancer. 2010 Jun 23;9(1):160.

Associating FLCN with colorectal cancer….thinking outside the box.

The development of renal cell carcinoma, fibrofolliculomas on the face and trunk and pneumothorax are the widely accepted ‘triad’ of symptoms associated with BHD Syndrome. It’s also important to consider that other clinical manifestations are associated (or at the very least, have been noted to co-occur) with BHD Syndrome in some cases. These include a range of benign and malignant tumours (detailed more fully by Menko et al, 2009*), but perhaps the association between colorectal cancer (CRC) and BHD syndrome is the most debated.

The earliest reports of BHD syndrome often described an association with CRC, but more recent genetic and clinical studies have provided conflicting data which only confuses matters further. A new article by Nahorski et al**, in the Journal of Medical Genetics, addresses this issue, and investigates the role of FLCN in sporadic CRC using combination of clinical and genetic methodologies. Their interesting results suggest that FLCN inactivation might contribute to colorectal tumourigenesis but you’ll have to read the paper yourself to find out the specifics (!). For me, this study represents an extremely informative investigation into an aspect of BHD Syndrome that’s ‘off the beaten trail’, since it doesn’t focus on the classic triad of symptoms previously mentioned, but is no less important, since identifying genotype-phenotype correlations could shed light on potential functional domains of the gene and in general adds to what we know about FLCN function.

Additionally, it’s important to keep in mind that the management and diagnosis of rarer diseases is often lead by current scientific findings (take the Menko* paper for example) and that providing medical professionals with a wider range of information about all the associated aspects of a disease is in the patient’s interest too.

*Menko FH et al, Birt-Hogg-Dubé syndrome: diagnosis and management. Lancet Oncol. 2009 Dec; 10(12):1199-206

**Nahorski M et al, Investigation of the Birt-Hogg-Dube tumour suppressor gene (FLCN) in familial and sporadic colorectal cancer. J Med Genet. 2010 Jun; 47(6):385-90.

Genetic variants in the Folliculin gene?

I attended the British Renal Society/Renal Association’s annual conference this week in Manchester, UK. It was well attended and addressed current clinical practice and basic research into a range renal disorders.  Unfortunately, there were no specific talks on BHD Syndrome but it was really interesting seeing how current renal genetics services were being integrated with established clinical pathways.

One specific talk on the subject of polycystic kidney disease highlighted the effect that certain genetic mutations can have on the phenotypic presentation of a disorder and I’d like to share that in the context of BHD.

We understand that BHD is a monogenic disorder, that is to say it’s caused by inactivation of a single gene, FLCN, which inevitably results in abnormal protein function within critical cell signalling pathways that underpin normal growth and development.

A range of causative pathogenic mutations have been identified (and even catalogued by Wei et al and Lim et al*). This has also lead to the development of a molecular diagnostic assay used to provide a positive diagnosis of BHD Syndrome.

It is essential to identify and characterise all mutations since some of these may act as pathogenic missense variants or hypomorphic alleles. Such mutations are not as immediately pathogenic as deleterious nonsense mutations but may be able to alter protein function if they arise within a highly conserved domain of the protein. They can account for milder phenotypes or even a disparity in the presentation of symptoms and significantly, rare missense variants can also be inherited and so give rise to familial disease.

*FLCN mutation databases by Wei et al:; and Lim et al:

A two-way street.

Amazingly, the BHD Research Blog has been going for nearly a year – my first post was way back in June 2009! It’s been an interesting period for me personally, expressing my opinion and thoughts on the ups and downs of BHD research and I hope to remain doing so for the foreseeable future. However what I can’t say is what’s going on in your lab right now and I think it’s something that would benefit all the scientists in the field…have you recently tried out a new FLCN antibody? Are you currently optimising a basic technique but having difficulties? This is what the BHD Resources forum was designed for. Go online and let people know if you’ve discovered something useful…by all means, don’t give away any confidential secrets, but a friendly ‘heads up’ could help out a BHD colleague!