Heterogeneous RNA editing and influence of ADAR2 on mesothelioma chemoresistance and the tumor microenvironment

We previously observed increased levels of adenosine-deaminase-acting-on-dsRNA (Adar)-dependent RNA editing during mesothelioma development in mice exposed to asbestos. The aim of this study was to characterize and assess the role of ADAR-dependent RNA editing in mesothelioma. We found that tumors and mesothelioma primary cultures have higher ADAR-mediated RNA editing compared to mesothelial cells. Unsupervised clustering of editing in different genomic regions revealed heterogeneity between tumor samples as well as mesothelioma primary cultures. ADAR2 expression levels are higher in BRCA1-associated protein 1 wild-type tumors, with corresponding changes in RNA editing in transcripts and 3'UTR. ADAR2 knockdown and rescue models indicated a role in cell proliferation, altered cell cycle, increased sensitivity to antifolate treatment, and type-1 interferon signaling upregulation, leading to changes in the microenvironment in vivo. Our data indicate that RNA editing contributes to mesothelioma heterogeneity and highlights an important role of ADAR2 not only in growth regulation in mesothelioma but also in chemotherapy response, in addition to regulating inflammatory response downstream of sensing nucleic acid structures.

Calpastatin participates in the regulation of cell migration in BAP1-deficient uveal melanoma cells

AIM

To detect how BRCA-associated protein 1 (BAP1) regulates cell migration in uveal melanoma (UM) cells.

METHODS

Wound healing and transwell assays were performed to detect UM cell migration abilities. Protein chip, immunoprecipitations and surface plasmon resonance analyses were applied to identify BAP1 protein partners. Western blot and calpain activity assays were used to test the expression and function of calpastatin (CAST).

RESULTS

CAST protein was confirmed as a new BAP1 protein partner, and loss of BAP1 reduced the expression and function of CAST in UM cells. The overexpression of CAST rescued the cell migration phenotype caused by BAP1 loss.

CONCLUSION

BAP1 interacts with CAST in UM cells, and CAST and its subsequent calpain pathway may mediate BAP1-related cell migration regulation.

BAP1 Germline Mutation Associated with Bilateral Primary Uveal Melanoma

Purpose

To describe the occurrence of bilateral primary uveal melanoma in 2 patients with mutation on the gene encoding BRCA1-associated protein 1 (BAP1).

Methods

Retrospective chart review of patients with bilateral primary uveal melanoma and subsequent positive germline BAP1 mutation.

Results

There were 2 patients with bilateral uveal melanoma and BAP1 germline positivity. Neither patient demonstrated oculodermal melanocytosis. Patient 1 underwent enucleation of his right eye (OD) at the age of 44 years for a 9.6-mm-thick choroidal melanoma. He returned 4 years later with a 10.0-mm-thick choroidal melanoma in his left eye (OS) and was treated with plaque radiotherapy. He had a strong family history of cancer, and clinical testing for germline BAP1 mutation identified a pathogenic mutation in BAP1. At the 18-month follow-up, visual acuity was 20/200 OS without evidence of systemic metastasis. Patient 2 initially presented at age 54 years with extensive, diffuse iris melanoma OD, initially treated with plaque radiotherapy, but local recurrence after 3 years necessitated enucleation. Four years later, a 6.0-mm-thick ciliary body melanoma OS was found and successfully treated with plaque radiotherapy. Clinical testing for germline BAP1 mutation identified a pathogenic mutation in BAP1. At the 8-year follow-up, visual acuity was 20/40 OS without evidence of local recurrence or systemic metastasis. The patient expired secondary to an unrelated brain infarction.

Conclusion

Bilateral uveal melanoma is exceedingly rare. Patients with bilateral uveal melanoma, especially when coincident with remote systemic cancers or a family history of cancer, should be evaluated for germline BAP1 mutation. Lifelong monitoring for related systemic malignancies is advised.