Differential expression of proteins belonging to the dystrophin family was analysed in peripheral nerves. In agreement with previous reports, no full-size dystrophin was detectable, only Dp116, one of the short dystrophin products of the Duchenne muscular dystrophy (DMD) gene. We used specific monoclonal antibodies to fully investigate the presence of utrophin, a dystrophin homologue encoded by a gene located on chromosome 6q24. Evidence is presented here of the presence of two potential isoforms of full-length utrophin in different nerve structures, which may differ by alternative splicing of the 3′-terminal part of the utrophin gene according to the specificities of the monoclonal antiobodies used. One full-length utrophin was co-localized with Dp116 in the sheath around each separate Schwann cell-axon unit, but the other utrophin isoform was found to be perineurium-specific. We also highlighted a potential 80 kDa utrophin-related protein. The utrophin distribution in peripheral nerves was re-evaluated and utrophin isoforms were detected at the protein level. This preliminary indication will require more concrete molecular evidence to confirm the presence of these two utrophin isoforms as well as the potential 80 kDa utrophin isoform, but the results strongly suggest that each isoform must have a specialized role and function within each specific nervous structure.

Resistance to castration is a crucial issue in the treatment of metastatic prostate cancer. Kinase inhibitors (KIs) have been tested as potential alternatives, but none of them are approved yet. KIs are subject of extensive metabolism at both the hepatic and the tumor level. Here, we studied the role of PXR (Pregnane X Receptor), a master regulator of metabolism, in the resistance to KIs in a prostate cancer setting. We confirmed that PXR is expressed in prostate tumors and is more frequently detected in advanced forms of the disease. We showed that stable expression of PXR in 22Rv1 prostate cancer cells conferred a resistance to dasatinib and a higher sensitivity to erlotinib, dabrafenib, and afatinib. Higher sensitivity to afatinib was due to a ~ 2-fold increase in its intracellular accumulation and involved the SLC16A1 transporter as its pharmacological inhibition by BAY-8002 suppressed sensitization of 22Rv1 cells to afatinib and was accompanied with reduced intracellular concentration of the drug. We found that PXR could bind to the SLC16A1 promoter and induced its transcription in the presence of PXR agonists. Together, our results suggest that PXR could be a biomarker of response to kinase inhibitors in castration-resistant prostate cancers.

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer in adults. Among the altered pathways leading to HCC, an increasing role is attributed to abnormal epigenetic regulation. Members of the Heterochromatin Protein (HP1) 1 family are key players in chromatin organisation, acting as docking sites for chromatin modifiers. Here, we inactivated HP1a in HepG2 human liver carcinoma cells and showed that HP1a participated in cell proliferation. HP1a-depleted cells have a global decrease in DNA methylation and consequently a perturbed chromatin organisation, as exemplified by the reactivation of transcription at centromeric and pericentromeric regions, eventhough the protein levels of chromatin writers depositing methylation marks, such as EZH2, SETDB1, SUV39H1, G9A and DNMT3A remained unaltered. This decrease was attributed mainly to a low S-Adenosyl Methionine level, a cofactor involved in methylation processes. Furthermore, we showed that this decrease was due to a modification in the Methionine adenosyl transferase 2A RNA level, which modifies the ratio of MAT1A/MAT2A, two enzymes that generate SAM. Importantly, HP1a reintroduction into HP1a-depleted cells restored the MAT2A protein to its initial level. Finally, we demonstrated that this transcriptional deregulation of MAT2A in HP1a-depleted cells relied on a lack of recruitment of HP1b and HP1g to MAT2A promoter where an improper non-CpG methylation site was promoted in the vicinity of the transcription start site where HP1b and HP1g bound. Altogether, these results highlight an unanticipated link between HP1 and the SAM synthesis pathway, and emphasise emerging functions of HP1s as sensors of some aspects of liver cell metabolism.

Repression of retro‐transposons is essential for genome integrity during germ cell development and is tightly controlled through epigenetic mechanisms. In primordial germ cells, Prmt5 is involved in retro‐transposon repression by methylating Piwi proteins, which is part of the piRNA pathway. Here, we show that in mice, genetic inactivation of coprs (which is highly expressed in testis and encodes a histone‐binding protein required for the targeting of Prmt5 activity) affects the maturation of spermatogonia to spermatids. Mass spectrometry analysis revealed the presence of Miwi in testis protein lysates immunoprecipitated with an anti‐Coprs antibody. The observed deregulation of Miwi and pachytene pre‐piRNAs levels, and the de‐repression of LINE1 repetitive sequences observed in coprs ‐/‐ mice, suggest that Coprs is implicated in genome surveillance mechanisms.

Chromatin organization is essential for appropriate interpretation of the genetic information. Here, we demonstrated that the chromatin associated proteins HP1 are dispensable for cell survival but are essential within hepatocytes to prevent liver tumor development. Molecular characterization of pre-malignant HP1-Triple KO livers revealed that HP1 are essential for the maintenance of the structural organization of heterochromatin but surprisingly, not for several well known heterochromatin functions such as the maintenance of the genome stability nor the regulation of major satellite repeat expression within liver. We further show that some specific retrotransposons, mainly of the ERV family, get reactivated in HP1-TKO livers correlating, in some cases, with the activation of the adjacent genes. We present evidence that this reactivation of ERV relies on the HP1-dependent ability of the corepressor TRIM28 to regulate KRAB-ZFP repressive activity. Intriguingly, we found that in contrast to the observation in young animals, the HP1-dependent maintenance of ERV silencing becomes independent of TRIM28 in old animals. Finally, we showed that HP1 are also essential directly or indirectly for the regulation of single genes with most of them having well characterized functions in liver homeostasis such as regulation of the redox and endoplasmic reticulum equilibrium, lipid metabolism and steroid biosynthesis.Altogether, our findings indicate that HP1 proteins, through the modulation of multiple chromatin-associated events both within the heterochromatic and euchromatic compartments, act as guardians of liver homeostasis to prevent tumor development.