Gentamicin-Induced Readthrough and Nonsense-Mediated mRNA Decay of SERPINB7 Nonsense Mutant Transcripts

Abstract

Nagashima-type palmoplantar keratosis (NPPK) is an autosomal recessive skin disorder with a high, unmet medical need that is caused by mutations in SERPINB7. Almost all NPPK patients carry the founder nonsense mutation c.796C>T (p.Arg266Ter) in the last exon of SERPINB7. Here we sought to determine whether topical nonsense-suppression (readthrough) therapy using gentamicin is applicable to NPPK. First, we demonstrated that gentamicin enhanced readthrough activity in cells transfected with SERPINB7 cDNA carrying the mutation and promoted full-length SERPINB7 protein synthesis in NPPK keratinocytes. We next conducted an investigator-blinded, randomized, bilaterally controlled compassionate use study of topical gentamicin in which five NPPK patients with c.796C>T were enrolled. Patients' self-reported improvement of hyperkeratosis was significantly greater on the gentamicin side than the control side (P = 0.0349). In two patients, hyperkeratosis was improved on the gentamicin side, as determined by a blinded-investigator assessment. These results indicate the therapeutic potential of topical gentamicin for NPPK. Unexpectedly, we also found that mutant SERPINB7 mRNAs harboring r.796c>u were degraded by nonsense-mediated mRNA decay. Furthermore, the truncated SERPINB7 protein was degraded via a proteasome-mediated pathway. These findings provide important insights into the mRNA/protein quality-control system in humans, which could be a potential therapeutic target for genetic diseases.

Treatment of hereditary hypotrichosis simplex of the scalp with topical gentamicin

“…In conclusion, we show that gentamicin may induce read-through across a nonsense mutation causing HSS, rescue corneodesmosin expression in cells of patients with HSS and clinically attenuate the clinical manifestations of the disease. Although systemic gentamicin treatment might be associated with nephrotoxicity and ototoxicity, these are less likely with topical administration to the skin as previously shown; 38 topical administration entails risk for contact allergic dermatitis. 39 The detection of trace amounts of gentamicin in the circulation of patients in the present trial and the fact that the drug restored hair growth in untreated areas suggest the need to assess the safety of gentamicin further in large, controlled, long-term (and possibly metronomic) studies.…”

“…Topical administration of gentamicin significantly improved hyperkeratosis. 38 Of note, both RDEB and NPPK are autosomal recessive conditions caused by complete or near-complete absence of protein biosynthesis; in contrast, HSS is a dominant disorder resulting from a putative toxic effect of a truncated protein. Hence, the consequences of gentamicin treatment are expected to be different in the two situations.…”

A Case of Malignant Melanoma Arising in Nagashima-type Palmoplantar Keratosis

“…According to the Human Genetic Variation Database and the 1000 Genomes browser, however, the frequency of mutant alleles carrying the most prevalent founder mutation, c.796C>T, is 0.091 in the Japanese population and 0.0152 in the Chinese population. Therefore, the estimated combined number of NPPK patients in these countries would be more than 0.3 million (9). Given that the estimated prevalence of MM in Japan is 0.0031% based on a national survey in 2014, there appears to be no significant difference in the incidence of MM between the patients with NPPK and the general population.…”

Hereditary palmoplantar keratoderma: A practical approach to the diagnosis

“…[67] Topical gentamicin for the treatment of Nagashima-type palmoplantar keratosis appears promising but needs clinical evaluation. [6869]…”