No abstract

VAP proteins (human VAPB/ALS8, Drosophila VAP33, and C. elegans VPR-1) are homologous proteins with an amino-terminal major sperm protein (MSP) domain and a transmembrane domain. The MSP domain is named for its similarity to the C. elegans MSP protein, a sperm-derived hormone that binds to the Eph receptor and induces oocyte maturation. A point mutation (P56S) in the MSP domain of human VAPB is associated with Amyotrophic lateral sclerosis (ALS), but the mechanisms underlying the pathogenesis are poorly understood. Here we show that the MSP domains of VAP proteins are cleaved and secreted ligands for Eph receptors. The P58S mutation in VAP33 leads to a failure to secrete the MSP domain as well as ubiquitination, accumulation of inclusions in the endoplasmic reticulum, and an unfolded protein response. We propose that VAP MSP domains are secreted and act as diffusible hormones for Eph receptors. This work provides insight into mechanisms that may impact the pathogenesis of ALS.

Despite nearly two decades since the discovery of gene fusions involving TFE3 or TFEB (“TFE”) in sporadic renal cell carcinoma (RCC), the molecular mechanisms underlying the renal-specific tumorigenesis remains largely unclear. The recent publication of the TCGA Network's clear cell kidney cancer paper provides further evidence for the importance of gene fusions by identifying 5 tumors harboring SFPQ-TFE3 fusions that otherwise lacked the common clear cell RCC associated mutation. Herein, we review key molecular features of TFE-fusion RCC, including candidate signaling pathways contributing to oncogenesis and a detailed overview of gene fusion isoforms based on an updated knowledge of TFE genetic organization. A total of 5 TFE3 gene fusions (PRCC-TFE3, ASPSCR1-TFE3, SFPQ-TFE3, NONO-TFE3, CLTC-TFE3) and 1 TFEB gene fusion (MALAT1-TFEB) have been identified in RCC tumors and characterized at the mRNA transcript level, with considerable heterogeneity in exon structure across different tumors, even for the same fusion partners. Common to all TFE3 and TFEB fusion isoforms is the retention of the wild-type protein C-terminus, including domains for DNA-binding, dimerization, and nuclear localization, but interestingly, not transcriptional activation. Despite this, the most widely accepted model explaining TFE-fusion oncogenesis remains the introduction of a constitutively active promoter leading to dysregulated TFE transcriptional activity. A multitude of molecular pathways well-implicated in carcinogenesis are regulated in part by TFE3 and/or TFEB protein, including activation of TGFβ and ETS transcription factors, E-cadherin expression, CD40L-dependent lymphocyte activation, mTORC1 signaling, insulin-dependent metabolism regulation, folliculin signaling, and Rb-dependent cell cycle arrest. Determining which pathways are most important will be critical to discovering the most promising therapeutic targets for this disease. Useful to this goal is a panel of cell lines derived from different TFE3-fusion RCC patient tumors, representing multiple fusion isoforms.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to biallelic inactivation of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH).Individuals with HLRCC are at risk to develop cutaneous and uterine leiomyomas and an aggressive form of kidney cancer. Pseudohypoxic drive-the aberrant activation of cellular hypoxia response pathways despite normal oxygen tension-is considered to be a likely mechanism underlying the etiology of this tumor. Pseudohypoxia requires the oxygen-independent stabilization of the ␣ subunit of the hypoxia-inducible transcription factor (HIF-1␣). Under normoxic conditions, proline hydroxylation of HIF-1␣ permits VHL recognition and subsequent targeting for proteasomal degradation. Here, we demonstrate that inactivating mutations of FH in an HLRCC-derived cell line result in glucose-mediated generation of cellular reactive oxygen species (ROS) and ROS-dependent HIF-1␣ stabilization. Additionally, we demonstrate that stable knockdown of FH in immortalized renal epithelial cells results in ROS-dependent HIF-1␣ stabilization. These data reveal that the obligate glycolytic switch present in HLRCC is critical to HIF stabilization via ROS generation.Patients with hereditary leiomyomatosis and renal cell cancer (HLRCC) harbor germ line mutations of the FH gene, which encodes the tricarboxylic acid cycle enzyme fumarate hydratase, and affected individuals are at risk for the development of leiomyomas of the skin and uterus (fibroids) as well as kidney cancer (11,25,37). Genetic analysis of tumor samples indicates that FH acts as a tumor suppressor gene (37). The renal tumors that develop in HLRCC patients are notable for their aggressiveness, and effective systemic therapies are lacking at this time. Hence, identification of the molecular mechanisms that underlie the pathogenesis of this disease is needed to facilitate the development of targeted therapeutic strategies. Moreover, such studies may provide further insight into the role of mitochondrial metabolism in both normal and aberrant cellular physiology.FH catalyzes the enzymatic step of the tricarboxylic (TCA) cycle that hydrates fumarate to form malate. Proposed mechanisms for HLRCC tumor formation include apoptotic resistance, oxidative stress, and pseudohypoxic drive (10). Of these, most reports to date support a role for pseudohypoxic drive, based specifically on studies of hypoxia-inducible transcription factor 1␣ (HIF-1␣) expression. Pseudohypoxia is defined as the aberrant activation of hypoxia response pathways under normal oxygen conditions. HIF-1␣ expression is elevated both in HLRCC tumor specimens and in normoxic cells in which FH expression has been transiently suppressed with small interfering RNA (siRNA) (16). HIF-2␣ expression is also elevated in HLRCC tumor samples, although to a lesser extent than is HIF-1␣. In addition, there is clear evidence of upregulated transcription of HIF target genes in HLRCC tumor samples and in FH siRNA-treated cells (16,30). Fur...