FOXC2disease-mutations identified in lymphedema-distichiasis patients cause both loss and gain of protein function

// Daniela Tavian 1 , Sara Missaglia 1 , Paolo E. Maltese 2 , Sandro Michelini 3 , Alessandro Fiorentino 3 , Maurizio Ricci 4 , Roberta Serrani 4 , Michael A. Walter 5,6 and Matteo Bertelli 2 1 Laboratory of Cellular Biochemistry and Molecular Biology, CRIBENS, Catholic University of the Sacred Heart, Milan, Italy 2 MAGI Non-Profit Human Medical Genetics Institute, Rovereto (TN), Italy 3 Department of Vascular Rehabilitation, San Giovanni Battista Hospital, Rome, Italy 4 Medicina Riabilitativa, Azienda Ospedaliero-Universitaria Ospedali Riuniti di Ancona, Torrette, Italy 5 Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada 6 Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, Alberta, Canada Correspondence to: Daniela Tavian, email: // Keywords : primary lymphedema, distichiasis, Foxc2 gene mutations, transcription factor, gain of function, Pathology Section Received : December 21, 2015 Accepted : May 22, 2016 Published : June 02, 2016 Abstract Dominant mutations in the FOXC2 gene cause a form of lymphedema primarily of the limbs that usually develops at or after puberty. In 90-95% of patients, lymphedema is accompanied by distichiasis. FOXC2 is a member of the forkhead/winged-helix family of transcription factors and plays essential roles in different developmental pathways and physiological processes. We previously described six unrelated families with primary lymphedema-distichiasis in which patients showed different FOXC2 mutations located outside of the forkhead domain. Of those, four were missense mutations, one a frameshift mutation, and the last a stop mutation. To assess their pathogenic potential, we have now examined the subcellular localization and the transactivation activity of the mutated FOXC2 proteins. All six FOXC2 mutant proteins were able to localize into the nucleus; however, the frameshift truncated protein appeared to be sequestered into nuclear aggregates. A reduction in the ability to activate FOXC1/FOXC2 response elements was detected in 50% of mutations, while the remaining ones caused an increase of protein transactivation activity. Our data reveal that either a complete loss or a significant gain of FOXC2 function can cause a perturbation of lymphatic vessel formation leading to lymphedema.