Arginine‐ but not alanine‐rich carboxy‐termini trigger nuclear translocation of mutant keratin 10 in ichthyosis with confetti

Abstract

Ichthyosis with confetti (IWC) is a genodermatosis associated with dominant‐negative variants in keratin 10 (KRT10) or keratin 1 (KRT1). These frameshift variants result in extended aberrant proteins, localized to the nucleus rather than the cytoplasm. This mislocalization is thought to occur as a result of the altered carboxy (C)‐terminus, from poly‐glycine to either a poly‐arginine or ‐alanine tail. Previous studies on the type of C‐terminus and subcellular localization of the respective mutant protein are divergent. In order to fully elucidate the pathomechanism of IWC, a greater understanding is critical. This study aimed to establish the consequences for localization and intermediate filament formation of altered keratin 10 (K10) C‐termini. To achieve this, plasmids expressing distinct KRT10 variants were generated. Sequences encoded all possible reading frames of the K10 C‐terminus as well as a nonsense variant. A keratinocyte line was transfected with these plasmids. Additionally, gene editing was utilized to introduce frameshift variants in exon 6 and exon 7 at the endogenous KRT10 locus. Cellular localization of aberrant K10 was observed via immunofluorescence using various antibodies. In each setting, immunofluorescence analysis demonstrated aberrant nuclear localization of K10 featuring an arginine‐rich C‐terminus. However, this was not observed with K10 featuring an alanine‐rich C‐terminus. Instead, the protein displayed cytoplasmic localization, consistent with wild‐type and truncated forms of K10. This study demonstrates that, of the various 3′ frameshift variants of KRT10, exclusively arginine‐rich C‐termini lead to nuclear localization of K10.

Discovery of heterozygous KRT10 alterations in MAUIE cases underlines the importance of regular skin cancer screening in ichthyosis with confetti

“…Almost 20% of patients develop nonmelanoma skin cancer (NMSC) in early adulthood, for unknown reasons. In all of the patients, heterozygous variants in either keratin (KRT) 10 or KRT1 genes have been found that lead to a shifted reading frame and translation into an aberrant carboxyl‐terminus of the protein 1–3…”

“…This switches the cellular localization of K10 from cytoplasm to nucleus (data not shown). 3 These results permit the deceased patients previously diagnosed with MAUIE to be reclassified as having IWC. However, both individuals also displayed alopecia and developed aggressive cSCC.…”

“…In all of the patients, heterozygous variants in either keratin (KRT) 10 or KRT1 genes have been found that lead to a shifted reading frame and translation into an aberrant carboxyl-terminus of the protein. [1][2][3] Two patients, male and female, with the characteristic clinical features of IWC including development of pale spots on congenital erythrodermic skin, 2 were formerly described as having MAUIE (micropinnae, alopecia universalis, ichthyosis, ectropion). 4,5 In addition, and untypical for IWC, they had developed numerous cutaneous squamous cell carcinomas (cSCCs).…”

“…The woman had a splice-site variant (c.1374-1G>C) that has been repeatedly described in IWC patients. 3 The man had a novel 14-bp deletion (c.1403_1417delinsA) ( Table 1). No further unknown or rare variants in KRT10/KRT1 were identified to explain the more severe phenotype in both patients, owing to compound heterozygosity.…”

“…B. Burger iD , 1 A. Ghosh iD , 1,2 C.K.Y. Ng iD , 3 S. Piscuoglio iD , 1,4 I. Spoerri iD , 1 P.H. Itin iD , 1,5 K. Greer 6 and D. Elbaum 7…”