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Biochemical properties of the recurrent LMX 1b truncated mutant carried in a Taiwanese family with nail‐patella syndrome
Author(s) -
Wang W.M.,
Chen J.F.,
Liu S.T.,
Hsu Y.J.,
Liu Y.C.,
Huang S.M.
Publication year - 2014
Publication title -
british journal of dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.304
H-Index - 179
eISSN - 1365-2133
pISSN - 0007-0963
DOI - 10.1111/bjd.13051
Subject(s) - haploinsufficiency , biology , transcription factor , mutant , transfection , microbiology and biotechnology , wild type , reporter gene , gene , promoter , genetics , gene expression , phenotype
Summary Background Loss of the DNA ‐binding activity of a transcription factor is detrimental to its function in responsive gene regulation. We diagnosed a Taiwanese family with nail‐patella syndrome ( NPS ) whose members inherited the mutated LMX 1b transcription factor with no DNA ‐binding homeodomain. The loss‐of‐function variants cause haploinsufficiency of LMX 1b, leading to the clinical manifestation of NPS . The underlying molecular mechanism is unclear. Objectives To test whether the recurrent pathogenic truncated LMX 1b‐R198X reported in our patients might be a functional protein. Its biochemical properties were explored. Methods The luciferase reporter driven by the human interleukin ( IL )‐6 gene promoter was assayed to measure the transcriptional activity of LMX 1b. The nuclear localization of different enhanced green fluorescent protein‐tagged LMX 1b proteins was observed using fluorescence microscopy. Western blotting was employed to evaluate the expression of various transfected LMX 1b constructs. Results LMX 1b‐R198X enhanced the IL ‐6 promoter activity activated by the wild‐type LMX 1b and diminished the promoter activity induced by phorbol 12‐myristate 13‐acetate. LMX 1b‐R198X carried out its effect differentially in the expression of various human genes. The nuclear localization of the wild‐type LMX 1b was disrupted by the C‐terminus truncation. The protein stability exhibited by LMX 1b‐R198X appears to be much higher than that of the wild‐type protein. Conclusions We demonstrated that loss of function might not be the only way for mutated LMX 1b to cause haploinsufficiency as the main pathogenic mechanism for NPS . LMX 1b‐R198X has less nuclear localization and higher stability than the wild‐type protein; consequently, it might function as a competitor to sequester other effectors by protein–protein interaction to interfere with downstream transcriptional events.