ESPE Abstracts (2014) 82 FC11.2

Novel SOX2 Mutation: Identification of New Molecular Mechanisms of SOX2 Action and Interactions

Kyriaki S. Alatzogloua, Cynthia L. Andoniadoub, Daniel Kelbermanc, Hyoong-Goo Kimd, Edward Botse-Baidood, Jennifer Pedersen-Whited, Lawrence Laymand, Juan Pedro Martinez-Barberab & Mehul T. Dattania

aDevelopmental Endocrinology Research Group, UCL Institute of Child Health, London, UK; bNeural Development Unit, UCL Institute of Child Health, London, UK; cDevelopmental Biology Unit, Ulverscroft Vision Research Group, UCL Institute of Child Health, London, UK; dSection of Endocrinology, Diabetes and Metabolism, Department of Medicine, The Medical College of Georgia, Augusta, USA

Background: SOX2 is an early developmental transcription factor implicated in pituitary development; heterozygous SOX2 mutations have been reported in patients with a severe ocular phenotype and hypogonadotrophic hypogonadism (HH) with/without associated abnormalities. SOX2 physically interacts with β-catenin, a member of the Wnt-signalling pathway, via its carboxyl-terminus and it represses in vitroβ-catenin mediated activation.

Objective and Hypotheses: We report a novel SOX2 mutation (c.G261T, p.K87N) in a female patient with bilateral congenital anophthalmia and developmental delay, who first presented at the age of 21 years with primary amenorrhoea. She had hypogonadotrophic hypogonadism (FSH 1.0 IU/L, LH 0.6 IU/L, Oestradiol <15 pg/mL) and thinning of the corpus callosum on MRI. The mutation occurred in the high-mobility group (HMG) DNA-binding domain. We studied its functional consequences, revealing a distinct mechanism of action.

Method: In vitro luciferase reporter assays, immunostaining and electrophoretic mobility shift assay (EMSA).

Results: Luciferase reporter assay showed that, unlike other mutations affecting the HMG domain, mutant p.K87N SOX2 had comparable transactivation to wild type (WT) SOX2 and it retained its ability to bind to a consensus DNA probe on EMSA. Nuclear localisation was confirmed by immunostaining. However, co-transfection of p.K87N SOX2 with a constitutively active form of human β-catenin (S33Y) in the TOPFLASH reporter assay, failed to repress β-catenin mediated activation. Neither WT nor p.K87N SOX2 bind to a TCF/LEF consensus probe on EMSA. Therefore, failure to repress β-catenin mediated activation in vitro may result from altered direct interaction β-catenin.

Conclusion: We report a novel SOX2 mutation in the HMG domain that, unexpectedly, fails to repress β-catenin mediated activation suggesting that the HMG domain is critical for the interaction with β-catenin. We report, for the first time to our knowledge, that clinical phenotypes may result from altered interaction between SOX2 and β-catenin.