Involvement of PBRM1 in VHL disease-associated clear cell renal cell carcinoma and its putative relationship with the HIF pathway.

Von Hippel-Lindau (VHL) disease is the main cause of inherited clear-cell renal cell carcinoma (ccRCC) and is caused by germline mutations in the VHL tumor suppressor gene. Bi-allelic VHL alterations lead to inactivation of pVHL, which plays a major role by downstream activation of the hypoxia inducible factor (HIF) pathway. Somatic VHL mutations occur in 80% of sporadic ccRCC cases and the second most frequently mutated gene is polybromo 1 (PBRM1). As there is currently no data regarding PBRM1 involvement in VHL disease-associated ccRCC, the aim of the present study was to assess the PBRM1 mutational status, and PBRM1 and HIF expression in VHL disease-associated ccRCC series compared with a sporadic series. PBRM1 gene was screened by Sanger sequencing for 23 VHL-disease-associated ccRCC and 22 sporadic ccRCC cases. Immunohistochemical studies were performed to detect the expression of PBRM1, HIF1 and HIF2 for all cases. In VHL-associated tumors, 13.0% (n=3/23) had PBRM1 somatic mutations and 17.4% (n=4/23) had a loss of PBRM1 nuclear expression. In sporadic cases, 27.3% (n=6/22) showed PBRM1 somatic mutations and 45.5% (n=10/22) had a loss of PBRM1 nuclear expression. Loss of PBRM1 was associated with an advanced tumor stage. HIF1-positive tumors were observed more frequently in the VHL-associated ccRCC than in the sporadic series. Furthermore, in the VHL cohort, PBRM1 expression appeared to be associated more with HIF1 than with HIF2. Given that hereditary tumors tend to be less aggressive, these results would suggest that co-expression of PBRM1 and HIF1 may have a less oncogenic role in VHL-associated ccRCC.

HLA-B27 alters BMP/TGFß signalling in Drosophila, revealing putative pathogenic mechanism for spondyloarthritis.

OBJECTIVES: The human leucocyte antigen (HLA)-B27 confers an increased risk of spondyloarthritis (SpA) by unknown mechanism. The objective of this work was to uncover HLA-B27 non-canonical properties that could explain its pathogenicity, using a new Drosophila model. METHODS: We produced transgenic Drosophila expressing the SpA-associated HLA-B*27:04 or HLA-B*27:05 subtypes, or the non-associated HLA-B*07:02 allele, alone or in combination with human ß2-microglobulin (hß2m), under tissue-specific drivers. Consequences of transgenes expression in Drosophila were examined and affected pathways were investigated by the genetic interaction experiments. Predictions of the model were further tested in immune cells from patients with SpA. RESULTS: Loss of crossveins in the wings and a reduced eye phenotype were observed after expression of HLA-B*27:04 or HLA-B*27:05 in Drosophila but not in fruit flies expressing the non-associated HLA-B*07:02 allele. These HLA-B27-induced phenotypes required the presence of hß2m that allowed expression of well-folded HLA-B conformers at the cell surface. Loss of crossveins resulted from a dominant negative effect of HLA-B27 on the type I bone morphogenetic protein (BMP) receptor saxophone (Sax) with which it interacted, resulting in elevated mothers against decapentaplegic (Mad, a Drosophila receptor-mediated Smad) phosphorylation. Likewise, in immune cells from patients with SpA, HLA-B27 specifically interacted with activin receptor-like kinase-2 (ALK2), the mammalian Sax ortholog, at the cell surface and elevated Smad phosphorylation was observed in response to activin A and transforming growth factor ß (TGFß). CONCLUSIONS: Antagonistic interaction of HLA-B27 with ALK2, which exerts inhibitory functions on the TGFß/BMP signalling pathway at the cross-road between inflammation and ossification, could adequately explain SpA development.

The endoplasmic reticulum unfolded protein response varies depending on the affected region of the tissue but independently from the source of stress.

Accumulation of unfolded proteins and calcium dyshomeostasis induces endoplasmic reticulum (ER) stress, which can be resolved by the unfolded protein response (UPR). We have previously reported that activation of the PERK/ATF4 branch of the UPR, by overexpressing Presenilin in part of the vestigial domain of Drosophila wing imaginal discs, induces both a caspase-dependent apoptosis and a Slpr/JNK/Dilp8-dependent developmental delay that allows compensation of cell death in the tissue. Recently, dDad1 depletion in Drosophila in engrailed-expressing cells of wing imaginal discs was also reported to activate the PERK/ATF4 branch but induced Mekk1/JNK-dependent apoptosis. Here, we assessed whether the stressed cell location in the wing imaginal disc could explain these differences in response to chronic ER stress or whether the stress source could be responsible for the signaling discrepancy. To address this question, we overexpressed a Rhodopsin-1 mutant prone to aggregate either in vestigial- or engrailed-expressing cells. We observed similar responses to the Presenilin overexpression in the vestigial domain and to the dDad1 depletion in the engrailed domain. Therefore, the consequences of a PERK/ATF4 branch activation depend on the position of the cell in the Drosophila wing imaginal disc, suggesting interactions of PERK signaling with developmental pathways involved in the determination or maintenance of wing domains.