Evaluation of the role of DKC1 overexpression in breast cancer

Dyskerin is part of the pseudouridylation complex and catalyzes the isomerization of uridines on ribosomal RNA (rRNA) into pseudouridines, guided by small nucleolar RNAs (snoRNAs). It is also part of the telomerase complex stabilizing the telomerase RNA component (hTR). Loss of function mutations in DKC1 cause X-linked Dyskeratosis Congenita (X-DC), a ribosomopathy characterized by failure of proliferating tissues and increased cancer susceptibility. Several human tumors show increased dyskerin expression and worse prognosis. Besides the role of dyskerin as tumor suppressor, literature lacks studies analyzing the function of its increased expression in tumors. In this work, we studied the effects of higher dyskerin expression generating stable DKC1 overexpression cell lines. We found that increasing dyskerin levels confers a more aggressive phenotype and increased translational efficiency independently on the translation initiation modality in untransformed mammary epithelial cells (MCF10A). Furthermore, DKC1 overexpression lead to an up-regulation of the snoRNAs pool, without any changes in the global pseudouridylation level of rRNA. Among the snoRNAs, three significantly up-regulated snoRNAs are known to target uridines on rRNA. We quantified the percentage of pseudouridines (Ψ) through a LC/MS based method on U1492 on 18S rRNA, U4975 and U1445 on 28S rRNA respectively. Our results show no significant changes in pseudouridine levels in these sites, although basing on the in vitro translation results, a biological role of the slight changes we detected cannot be excluded. Finally, patients harboring tumors with higher dyskerin expression have worse prognosis, lower disease-free survival and advanced lymph node status respect of patients expressing low dyskerin levels. Tumors with higher dyskerin expression, have higher levels of SNORA64, SNORA70 and SNORA67. In conclusion, our work indicates for the first time that dyskerin may act as an oncogene in breast cancer, promoting neoplastic transformation from early stage and providing ribosomes with a major translation efficiency.