A Ribosomopathy Reveals Decoding Defective Ribosomes Driving Human Dysmorphism.

Ribosomal protein (RP) gene mutations, mostly associated with inherited or acquired bone marrow failure, are believed to drive disease by slowing the rate of protein synthesis. Here de novo missense mutations in the RPS23 gene, which codes for uS12, are reported in two unrelated individuals with microcephaly, hearing loss, and overlapping dysmorphic features. One individual additionally presents with intellectual disability and autism spectrum disorder. The amino acid substitutions lie in two highly conserved loop regions of uS12 with known roles in maintaining the accuracy of mRNA codon translation. Primary cells revealed one substitution severely impaired OGFOD1-dependent hydroxylation of a neighboring proline residue resulting in 40S ribosomal subunits that were blocked from polysome formation. The other disrupted a predicted pi-pi stacking interaction between two phenylalanine residues leading to a destabilized uS12 that was poorly tolerated in 40S subunit biogenesis. Despite no evidence of a reduction in the rate of mRNA translation, these uS12 variants impaired the accuracy of mRNA translation and rendered cells highly sensitive to oxidative stress. These discoveries describe a ribosomopathy linked to uS12 and reveal mechanistic distinctions between RP gene mutations driving hematopoietic disease and those resulting in developmental disorders.

Recurring mutations in RPL15 are linked to hydrops fetalis and treatment independence in Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a rare inherited bone marrow failure disorder linked predominantly to ribosomal protein gene mutations. Here the European DBA consortium reports novel mutations identified in the RPL15 gene in 6 unrelated individuals diagnosed with DBA. Although point mutations have not been previously reported for RPL15, we identified 4 individuals with truncating mutations p.Tyr81* (in 3 of 4) and p.Gln29*, and 2 with missense variants p.Leu10Pro and p.Lys153Thr. Notably, 75% (3 of 4) of truncating mutation carriers manifested with severe hydrops fetalis and required intrauterine transfusions. Even more remarkable is the observation that the 3 carriers of p.Tyr81* mutation became treatment-independent between four and 16 months of life and maintained normal blood counts until their last follow up. Genetic reversion at the DNA level as a potential mechanism of remission was not observed in our patients. In vitro studies revealed that cells carrying RPL15 mutations have pre-rRNA processing defects, reduced 60S ribosomal subunit formation, and severe proliferation defects. Red cell culture assays of RPL15-mutated primary erythroblast cells also showed a severe reduction in cell proliferation, delayed erythroid differentiation, elevated TP53 activity, and increased apoptosis. This study identifies a novel subgroup of DBA with mutations in the RPL15 gene with an unexpected high rate of hydrops fetalis and spontaneous, long-lasting remission.

Ribosome profiling uncovers selective mRNA translation associated with eIF2 phosphorylation in erythroid progenitors.

The regulation of translation initiation factor 2 (eIF2) is important for erythroid survival and differentiation. Lack of iron, a critical component of heme and hemoglobin, activates Heme Regulated Inhibitor (HRI). This results in phosphorylation of eIF2 and reduced eIF2 availability, which inhibits protein synthesis. Translation of specific transcripts such as Atf4, however, is enhanced. Upstream open reading frames (uORFs) are key to this regulation. The aim of this study is to investigate how tunicamycin treatment, that induces eIF2 phosphorylation, affects mRNA translation in erythroblasts. Ribosome profiling combined with RNA sequencing was used to determine translation initiation sites and ribosome density on individual transcripts. Treatment of erythroblasts with Tunicamycin (Tm) increased phosphorylation of eIF2 2-fold. At a false discovery rate of 1%, ribosome density was increased for 147 transcripts, among which transcriptional regulators such as Atf4, Tis7/Ifrd1, Pnrc2, Gtf2h, Mbd3, JunB and Kmt2e. Translation of 337 transcripts decreased more than average, among which Dym and Csde1. Ribosome profiling following Harringtonine treatment uncovered novel translation initiation sites and uORFs. Surprisingly, translated uORFs did not predict the sensitivity of transcripts to altered ribosome recruitment in presence or absence of Tm. The regulation of transcription and translation factors in reponse to eIF2 phosphorylation may explain the large overall response to iron deficiency in erythroblasts.

Seroreactivity to epidermodysplasia verruciformis-related human papillomavirus types is associated with nonmelanoma skin cancer.

DNA from epidermodysplasia verruciformis-related human papillomavirus (EV-HPV) types is frequently found in nonmelanoma skin cancer (squamous and basal cell carcinoma). Epidemiological studies that investigate the relation between EV-HPV infection and nonmelanoma skin cancer are scarce. We designed a case-control study in which we looked for HPV infection in 540 cases with a history of skin cancer and 333 controls. By measuring seroreactivity to L1 virus-like particles of EV-HPV types 5, 8, 15, 20, 24, and 38 and the genital type HPV16 and by estimating the skin cancer relative risk among HPV seropositives, we analyzed whether EV-HPV serorecognition is associated with nonmelanoma skin cancer. Seroreactivity to five of the six EV-HPV types tested (HPV5, 8, 15, 20, and 24) was significantly increased in the squamous cell carcinoma cases. After adjusting for age and sex, the estimated squamous cell carcinoma relative risk was significantly increased in HPV8 and HPV38 seropositives [odds ratio (OR) = 14.7 (95% confidence interval (CI), 1.6-135) and OR = 3.0 (95% CI, 1.1-8.4), respectively]. The estimated relative risk for nodular and superficial multifocal basal cell carcinoma was also significantly increased in the HPV8 seropositives [OR = 9.2 (95% CI, 1.1-78.2) and OR = 17.3 (95% CI, 2.1-143), respectively] and in the HPV20 seropositives [OR = 3.2 (95% CI 1.3-7.9) and OR = 3.4 (95% CI 1.2-9.5), respectively]. The relative risk of developing malignant melanoma was not increased among HPV seropositives, and no associations were found for HPV16. Restricted analyses among the HPV seropositives only, to exclude distortion by interindividual differences in seroresponsiveness, underscored the significance of our findings. Restricted analyses among patients with skin cancer only, however, revealed that EV-HPV seropositivity was not significantly more present in patients with nonmelanoma skin cancer than in those with melanoma skin cancer. Taken together, our results indicate that EV-HPV serorecognition is nonspecifically associated with nonmelanoma skin cancer and suggest that EV-HPV-directed seroresponses are induced upon skin cancer formation, rather than upon infection.