Human 53BP1 is primarily known as a key player in regulating DNA double strand break (DSB) repair choice; however, its involvement in other biological process is less well understood. Here, we report a previously uncharacterized function of 53BP1 at heterochromatin, where it undergoes liquid-liquid phase separation (LLPS) with the heterochromatin protein HP1α in a mutually dependent manner. Deletion of 53BP1 results in a reduction in heterochromatin centers and the de-repression of heterochromatic tandem repetitive DNA. We identify domains and residues of 53BP1 required for its LLPS, which overlap with, but are distinct from, those involved in DSB repair. Further, 53BP1 mutants deficient in DSB repair, but proficient in LLPS, rescue heterochromatin de-repression and protect cells from stress-induced DNA damage and senescence. Our study suggests that in addition to DSB repair modulation, 53BP1 contributes to the maintenance of heterochromatin integrity and genome stability through LLPS.

Melanoma is the most lethal skin cancer, with increasing incidence worldwide. The molecular events that drive melanoma development and progression have been extensively studied, resulting in significant improvements in diagnostics and therapeutic approaches. However, a high drug resistance to targeted therapies and adverse effects of immunotherapies are still a major challenge in melanoma treatment. Therefore, the elucidation of molecular mechanisms of melanomagenesis and cancer response to treatment is of great importance. Recently, many studies have revealed the close association of long noncoding RNAs (lncRNAs) with the development of many cancers, including melanoma. These RNA molecules are able to regulate a plethora of crucial cellular processes including proliferation, differentiation, migration, invasion and apoptosis through diverse mechanisms, and even slight dysregulation of their expression may lead to tumorigenesis. lncRNAs are able to bind to protein complexes, DNA and RNAs, affecting their stability, activity, and localization. They can also regulate gene expression in the nucleus. Several functions of lncRNAs are context-dependent. This review summarizes current knowledge regarding the involvement of lncRNAs in melanoma. Their possible role as prognostic markers of melanoma response to treatment and in resistance to therapy is also discussed

MicroRNAs (miRNAs), which are small non-coding RNA molecules that post-transcriptionally regulate the expression of target genes, control the vast majority of cellular events, including proliferation, differentiation, survival, senescence, autophagy, metabolism and genome stability. Even slight alterations in miRNA expression levels may induce the development of pathological states, including cancer. Several studies have already demonstrated the importance of miRNAs in the regulation of melanocytes. Upregulation of oncogenic miRNAs (oncomiRs), mainly by amplification and translocation of miRNA genes, and downregulation of oncosuppressor miRNAs (anti-oncomiRs) by deletion and other mutations, promoter methylation and abnormal processing contributes to melanoma initiation and progression. At each phase of melanoma progression, tumor cells exhibit distinct profiles of miRNA expression, as compared with normal melanocytes. Moreover, as miRNAs are stable molecules that can be identified in bodily fluids, such as blood and saliva, they can serve as potent non-invasive prognostic markers of disease progression and response to therapy. This review summarizes recent findings regarding miRNA-mediated control of melanocytes and melanoma development, and presents miRNAs as prognostic markers for this disease.

Background/Aim: MicroRNAs (miRNAs) transported in melanoma-derived exosomes function as intercellular messengers supporting tumor survival and progression. Hypoxia increases melanoma phenotypic plasticity, drug resistance, and metastasis. Materials and Methods: We determined the miRNA profiles in exosomes derived from melanoma cells grown under hypoxic and normoxic conditions by microarray analyses and reverse transcription-polymerase chain reaction (RT-PCR) in order to analyze the potential influence of vesicle-transported miRNAs on cancer-related pathways and transcriptional programs. Results: Despite phenotypical differences of the four cell lines used, their exosomes shared the majority of miRNAs. The levels of three miRNAs were higher in normoxic exosomes, whereas 15 miRNAs were significantly more abundant under hypoxic conditions. Pathway analysis pointed at several cellular processes contributing to proliferation, drug resistance, and modification of the tumor microenvironment, including immunosuppression. Conclusion: The miRNA-expression profiles of exosomes from patient-derived melanoma cells are modified by oxygen concentration and reflect the phenotypic changes of melanoma cells under different growth conditions.