Development of hypomelanotic macules is associated with constitutive activated mTORC1 in tuberous sclerosis complex

• Published in: Molecular genetics and metabolism 2017-04, Vol.120 (4), p.384-391
• Main Authors: Møller, Lisbeth Birk, Schönewolf-Greulich, Bitten, Rosengren, Thomas, Larsen, Lasse Jonsgaard, Ostergaard, John R., Sommerlund, Mette, Ostenfeldt, Caroline, Stausbøl-Grøn, Brian, Linnet, Karen Markussen, Gregersen, Pernille Axél, Jensen, Uffe Birk
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution; Cells, Cultured; Down-Regulation; Female; Fibroblasts - cytology; Fibroblasts - metabolism; Humans; Hypomelanotic macules; Male; Mechanistic Target of Rapamycin Complex 1; mTOR; Multiprotein Complexes - genetics; Multiprotein Complexes - metabolism; Pedigree; RNA Splicing; Sequence Analysis, DNA; Silent substitution; Skin Diseases - genetics; Skin Diseases - metabolism; Skin Diseases - pathology; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism; TSC; TSC2; Tuberous Sclerosis - complications; Tuberous Sclerosis - genetics; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins - genetics
• ISSN: 1096-7192; 1096-7206
• DOI: 10.1016/j.ymgme.2017.02.008

TSC1 and TSC2 are genes mutated in the syndrome TSC (tuberous sclerosis complex). We describe a 3-generation family with 17 affected members, all presenting classic TSC features except renal manifestations. The disease segregates with a silent substitution in TSC2, c.4149C>T, p.(Ser1838Ser), which leads to the formation of an active donor splice site, resulting in three shorter alternatively spliced transcripts with premature stop codons. However a small amount of normal spliced transcript is apparently produced from the mutated allele, which might explain the milder phenotype. The gene products of TSC1/2 form a complex which at energy limiting states, down-regulates the activity of the regulator of protein synthesis, the mammalian target of rapamycin complex1 (mTORC1). As expected, in contrast to cultured control fibroblasts, starvation of cultured patient fibroblasts obtained from a hypomelanotic macule did not lead to repression of mTORC1, whereas partial repression was observed in patient fibroblasts obtained from non-lesional skin. The findings indicate that the development of hypomelanotic macules is associated with constitutive activated mTORC1, whereas mild deregulation of mTORC1 allows the maintenance of normal skin. Furthermore, the finding establishes the pathogenic effect of the “silent” c.4149C>T substitution and emphasizes the need for awareness when interpreting silent substitutions in general. •Development of hypomelanotic macules in TSC is associated with constitutive activated mTORC1.•Mild deregulation of mTORC1 allows the maintenance of normal skin.•The silent substitution, c.4149C>T must indeed be pathogenic leading to TSC.