Hanson D, Stevens A, Murray PG, Black GC, Clayton PE

Mutations in CUL7, OBSL1 and CCDC8, leading to disordered ubiquitination, cause one of the commonest primordial growth disorders, 3-M syndrome. This condition is associated with (1) abnormal p53 function, (2) GH and/or IGF1 resistance, which may relate to failure to recycle signalling molecules, and (3) cellular IGF2 deficiency. However the ...

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exact molecular mechanisms that may link these abnormalities generating growth restriction remain undefined. Here we have used immunoprecipitation/mass spectrometry (IP/MS) and transcriptomic studies to generate a 3-M 'interactome', to define key cellular pathways and biological functions associated with growth failure seen in 3-M. We identified 189 proteins which all interacted with CUL7, OBSL1 and CCDC8, from which a network including 176 of these proteins was generated. To strengthen the association to 3-M syndrome, these proteins were compared to an inferred network generated from the genes that were differentially expressed in 3-M fibroblasts compared to controls. This resulted in a final 3-M network of 131 proteins, with the most significant biological pathway within the network being mRNA splicing/processing. We have shown using an exogenous insulin receptor (INSR) minigene system that alternative splicing of exon 11 is significantly changed in HEK293 cells with altered expression of CUL7, OBSL1 and CCDC8 and in 3-M fibroblasts. The net result is a reduction in expression of the mitogenic INSR isoform in 3-M syndrome. From these preliminary data we hypothesise that disordered ubiquitination could result in aberrant mRNA splicing in 3-M however further investigation is required to determine if this contributes to growth failure.

Date: Apr. 07, 2014

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