A new human dyskerin isoform with cytoplasmic localization

Background: The human DKC1 gene is causative of X-linked dyskeratosis congenita (X-DC), a syndrome characterized by mucocutaneous features, bone marrow failure, tumor susceptibility, perturbation of stem cell function, and premature aging. DKC1 is thought to produce a single protein, named dyskerin, which shows strict nucleolar localization and participates in at least two distinct nuclear functional complexes: the H/ACA small nucleolar ribonucleoproteic complex involved in RNA pseudouridylation and the active Telomerase complex.

Methods: By bioinformatics and molecular analyses we identified a DKC1 splice variant able to encode a truncated form of dyskerin, confirmed its active expression in diverse human tissues by RT-PCR, and showed by immunoblotting and immunocytochemistry experiments that it actually encodes a novel protein. Stably transfected clones over-expressing the new isoform were analyzed for growth, morphology and adhesion properties.

Results: Our results show that DKC1 encodes a new alternatively spliced mRNA able to direct the synthesis of a variant dyskerin with unexpected cytoplasmic localization. Intriguingly, when over-expressed in HeLa cells, the new isoform promotes cell to cell and cell to substratum adhesion, increases the cell proliferation rate and leads to cytokeratin hyper-expression.

Conclusions and general significance: Our results highlight a novel degree of complexity and regulation of the human DKC1 gene and reveal that it can play a further, unpredicted role in cell adhesion. The identification of a dyskerin cytoplasmic variant reinforces the view that other mechanisms, in addition to telomere instability, can significantly contribute to the pathogenesis of the X-DC, and suggests that DKC1 nucleolar and cytoplasmic functions might cumulatively account for the plethora of manifestations displayed by this syndrome.