SUMMARY Synovial sarcoma is a translocation-associated sarcoma where the underlying chromosomal event generates SS18-SSX fusion transcripts. In vitro and in vivo studies have shown that the SS18-SSX fusion oncoprotein is both necessary and sufficient to support tumorigenesis; however, its mechanism of action remains poorly defined. We have purified a core SS18-SSX complex and discovered that SS18-SSX serves as a bridge between activating transcription factor 2 (ATF2) and transducin-like enhancer of split 1 (TLE1), resulting in repression of ATF2 target genes. Disruption of these components by siRNA knockdown or treatment with HDAC inhibitors rescues target gene expression, leading to growth suppression and apoptosis. Together, these studies define a fundamental role for aberrant ATF2 transcriptional dysregulation in the etiology of synovial sarcoma.

Mutations in the NIPA1(SPG6) gene, named for "nonimprinted in Prader-Willi/Angelman" has been implicated in one form of autosomal dominant hereditary spastic paraplegia (HSP), a neurodegenerative disorder characterized by progressive lower limb spasticity and weakness. However, the function of NIPA1 is unknown. Here, we show that reduced magnesium concentration enhances expression of NIPA1 suggesting a role in cellular magnesium metabolism. Indeed NIPA1 mediates Mg 2؉ uptake that is electrogenic, voltage-dependent, and saturable with a Michaelis constant of 0.69 ؎ 0.21 mM when expressed in Xenopus oocytes. Subcellular localization with immunofluorescence showed that endogenous NIPA1 protein associates with early endosomes and the cell surface in a variety of neuronal and epithelial cells. As expected of a magnesiumresponsive gene, we find that altered magnesium concentration leads to a redistribution between the endosomal compartment and the plasma membrane; high magnesium results in diminished cell surface NIPA1 whereas low magnesium leads to accumulation in early endosomes and recruitment to the plasma membrane. The mouse NIPA1 mutants, T39R and G100R, corresponding to the respective human mutants showed a loss-offunction when expressed in oocytes and altered trafficking in transfected COS7 cells. We conclude that NIPA1 normally encodes a Mg 2؉ transporter and the loss-of function of NIPA1(SPG6) due to abnormal trafficking of the mutated protein provides the basis of the HSP phenotype.The NIPA1 [NT_078094] gene is named for "nonimprinted in Prader-Willi/Angelman" because it was thought to be located among about 30 imprinted genes linked to chromosome 15q11-q13 (SPG6 locus) involved in the Prader-Willi syndrome (1-5). However, NIPA1 has also been implicated in another distinct disorder termed autosomal dominant hereditary spastic paraplegia (HSP) 4 (OMIM 608145 and 600363). HSP comprises more than 30 genetic disorders whose predominant feature is a spastic gait (6). Mutations in at least six genes have been associated with autosomal dominant HSP including NIPA1(SPG6). This heterogenous group presents with progressive lower limb spasticity and weakness. In the absence of other clinical features these disorders are referred to as pure or uncomplicated HSP (6). Fink et al. (7,8) reported that uncomplicated HSP was linked to chromosome 15q, the region of NIPA1. Additional studies by this group identified a nucleotide substitution at position 134 of the NIPA1 cDNA that resulted in an amino acid substitution at position 45 of the NIPA1 protein (T45R) in SPG6-linked HSP kindred and in an unrelated kindred that was too small for linkage analysis (9). More recently, three different research groups have identified a missense substitution in NIPA1, G106R, in a number of large unrelated families (10 -12). The functional role of NIPA1 in Prader-Willi or HSP syndromes has not been determined.Magnesium is the second most abundant cation within the cell and plays an important role in many intracellular biochemical functions ...

Goytain, Angela, and Gary A. Quamme. Functional characterization of human SLC41A1, a Mg 2ϩ transporter with similarity to prokaryotic MgtE Mg 2ϩ transporters.

Purpose: Gene fusions involving neuregulin 1 (NRG1) have been noted in multiple cancer types and have potential therapeutic implications. Although varying results have been reported in other cancer types, the efficacy of the HER-family kinase inhibitor afatinib in the treatment of NRG1 fusionpositive pancreatic ductal adenocarcinoma is not fully understood. Experimental Design: Forty-seven patients with pancreatic ductal adenocarcinoma received comprehensive wholegenome and transcriptome sequencing and analysis. Two patients with gene fusions involving NRG1 received afatinib treatment, with response measured by pretreatment and posttreatment PET/CT imaging. Results: Three of 47 (6%) patients with advanced pancreatic ductal adenocarcinoma were identified as KRAS wild type by whole-genome sequencing. All KRAS wild-type tumors were positive for gene fusions involving the ERBB3 ligand NRG1. Two of 3 patients with NRG1 fusion-positive tumors were treated with afatinib and demonstrated a significant and rapid response while on therapy. Conclusions: This work adds to a growing body of evidence that NRG1 gene fusions are recurrent, therapeutically actionable genomic events in pancreatic cancers. Based on the clinical outcomes described here, patients with KRAS wildtype tumors harboring NRG1 gene fusions may benefit from treatment with afatinib. See related commentary by Aguirre, p. 4589

BackgroundIntracellular magnesium is abundant, highly regulated and plays an important role in biochemical functions. Despite the extensive evidence for unique mammalian Mg2+ transporters, few proteins have been biochemically identified to date that fulfill this role. We have shown that epithelial magnesium conservation is controlled, in part, by differential gene expression leading to regulation of Mg2+ transport. We used this knowledge to identify a novel gene that is regulated by magnesium.ResultsOligonucleotide microarray analysis was used to identify a novel human gene that encodes a protein involved with Mg2+-evoked transport. We have designated this magnesium transporter (MagT1) protein. MagT1 is a novel protein with no amino acid sequence identity to other known transporters. The corresponding cDNA comprises an open reading frame of 1005 base pairs encoding a protein of 335 amino acids. It possesses five putative transmembrane (TM) regions with a cleavage site, a N-glycosylation site, and a number of phosphorylation sites. Based on Northern analysis of mouse tissues, a 2.4 kilobase transcript is present in many tissues. When expressed in Xenopus laevis oocytes, MagT1 mediates saturable Mg2+ uptake with a Michaelis constant of 0.23 mM. Transport of Mg2+ by MagT1 is rheogenic, voltage-dependent, does not display any time-dependent inactivation. Transport is very specific to Mg2+ as other divalent cations did not evoke currents. Large external concentrations of some cations inhibited Mg2+ transport (Ni2+, Zn2+, Mn2+) in MagT1-expressing oocytes. Ca2+and Fe2+ were without effect. Real-time reverse transcription polymerase chain reaction and Western blot analysis using a specific antibody demonstrated that MagT1 mRNA and protein is increased by about 2.1-fold and 32%, respectively, in kidney epithelial cells cultured in low magnesium media relative to normal media and in kidney cortex of mice maintained on low magnesium diets compared to those animals consuming normal diets. Accordingly, it is apparent that an increase in mRNA levels is translated into higher protein expression.ConclusionThese studies suggest that MagT1 may provide a selective and regulated pathway for Mg2+ transport in epithelial cells.