Telomerase RNA Mutated in Autosomal Dyskeratosis Congenita Reconstitutes a Weakly Active Telomerase Enzyme Defective in Telomere Elongation

Abstract

Dyskeratosis congenita (DC) is a rare multi-system syndrome characterized by naildystrophy, abnormal skin pigmentation and mucosal leukoplakia. The gene mutated in the Xlinkedform of human DC encodes for dyskerin, a nucleolar pseudourydilase that is involved inrRNA maturation. Dyskerin is also involved in telomerase function through its interaction withthe telomerase RNA (hTR). Mutations in dyskerin result in low levels of hTR, decreasedtelomerase activity and telomere shortening. Autosomal dominant DC is characterized bymutations in hTR, supporting the hypothesis that the DC phenotype may be caused by impairedtelomere maintenance. Several mutations have been identified in different regions of hTR inpatients affected by autosomal dominant DC. Recent reports have shown that co-expression ofwild-type hTR with hTR harboring mutations found in the pseudoknot domain does not affecttelomerase activity in vitro. However, these studies did not assess the consequences of mutanthTR expression at the telomeres. Here we provide the first direct in vivo evidence that a mutanthTR carrying the GC to AG double substitution in the pseudoknot at nucleotides 107-108 foundin patients affected by autosomal dominant DC does not behave as a dominant-negative fortelomere maintenance. Rather it reconstitutes a weakly active telomerase enzyme, which isdefective in telomere elongation.