StAR Enhances Transcription of Genes Encoding the Mitochondrial Proteases Involved in Its Own Degradation

Steroidogenic acute regulatory protein (StAR) is essential for steroid hormone synthesis in the adrenal cortex and the gonads. StAR activity facilitates the supply of cholesterol substrate into the inner mitochondrial membranes where conversion of the sterol to a steroid is catalyzed. Mitochondrial import terminates the cholesterol mobilization activity of StAR and leads to mounting accumulation of StAR in the mitochondrial matrix. Our studies suggest that to prevent mitochondrial impairment, StAR proteolysis is executed by at least 2 mitochondrial proteases, ie, the matrix LON protease and the inner membrane complexes of the metalloproteases AFG3L2 and AFG3L2: SPG7/paraplegin. Gonadotropin administration to prepubertal rats stimulated ovarian follicular development associated with increased expression of the mitochondrial protein quality control system. In addition, enrichment of LON and AFG3L2 is evident in StAR-expressing ovarian cells examined by confocal microscopy. Furthermore, reporter studies of the protease promoters examined in the heterologous cell model suggest that StAR expression stimulates up to a 3.5-fold increase in the protease gene transcription. Such effects are StAR-specific, are independent of StAR activity, and failed to occur upon expression of StAR mutants that do not enter the matrix. Taken together, the results of this study suggest the presence of a novel regulatory loop, whereby acute accumulation of an apparent nuisance protein in the matrix provokes a mitochondria to nucleus signaling that, in turn, activates selected transcription of genes encoding the enrichment of mitochondrial proteases relevant for enhanced clearance of StAR

Transcriptional activation of LON Gene by a new form of mitochondrial stress: A role for the nuclear respiratory factor 2 in StAR overload response (SOR)

High output of steroid hormone synthesis in steroidogenic cells of the adrenal cortex and the gonads requires the expression of the steroidogenic acute regulatory protein (StAR) that facilitates cholesterol mobilization to the mitochondrial inner membrane where the CYP11A1/P450scc enzyme complex converts the sterol to the first steroid. Earlier studies have shown that StAR is active while pausing on the cytosolic face of the outer mitochondrial membrane while subsequent import of the protein into the matrix terminates the cholesterol mobilization activity. Consequently, during repeated activity cycles, high level of post-active StAR accumulates in the mitochondrial matrix. To prevent functional damage due to such protein overload effect, StAR is degraded by a sequence of three to four ATP-dependent proteases of the mitochondria protein quality control system, including LON and the m-AAA membranous proteases AFG3L2 and SPG7/paraplegin. Furthermore, StAR expression in both peni-ovulatory ovarian cells, or under ectopic expression in cell line models, results in up to 3-fold enrichment of the mitochondrial proteases and their transcripts. We named this novel form of mitochondrial stress as StAR overload response (SOR). To better understand the SOR mechanism at the transcriptional level we analyzed first the unexplored properties of the proximal promoter of the LON gene. Our findings suggest that the human nuclear respiratory factor 2 (NRF-2), also known as GA binding protein (GABP), is responsible for 88% of the proximal promoter activity, including the observed increase of transcription in the presence of StAR. Further studies are expected to reveal if common transcriptional determinants coordinate the SOR induced transcription of all the genes encoding the SOR proteases. (C) 2015 Elsevier Ireland Ltd. All rights reserved

Snord 3A: a molecular marker and modulator of prion disease progression.

Since preventive treatments for prion disease require early identification of subjects at risk, we searched for surrogate peripheral markers characterizing the asymptomatic phases of such conditions. To this effect, we subjected blood mRNA from E200K PrP CJD patients and corresponding family members to global arrays and found that the expression of Snord3A, a non-coding RNA transcript, was elevated several times in CJD patients as compared to controls, while asymptomatic carriers presented intermediate Snord3A levels. In the brains of TgMHu2ME199K mice, a mouse model mimicking for E200K CJD, Snord 3A levels were elevated in an age and disease severity dependent manner, as was the case for brains of these mice in which disease was exacerbated by copper administration. Snord3A expression was also elevated in scrapie infected mice, but not in PrP(0/0) mice, indicating that while the expression levels of this transcript may reflect diverse prion etiologies, they are not related to the loss of PrP(C)'s function. Elevation of Snord3A was consistent with the activation of ATF6, representing one of the arms of the unfolded protein response system. Indeed, SnoRNAs were associated with reduced resistance to oxidative stress, and with ER stress in general, factors playing a significant role in this and other neurodegenerative conditions. We hypothesize that in addition to its function as a disease marker, Snord3A may play an important role in the mechanism of prion disease manifestation and progression

Identification of Snord3A and Aldh1A1 as disease specific markers.

<p>a: Gene expression heat map representing the levels of transcripts expressed in blood from E200KCJD patients, carriers and non-carriers control. b: Snord3A expression level in microarrays of patients and healthy mutation carriers as compared to non-carrier controls. C: Aldh1A1 expression level in patients and healthy mutation carriers as compared to non-carrier controls (P value <0.005).</p

Expression of Snord3A in scrapie-infected brain’s.

<p><u>Main picture</u>: Total RNA from brains of scrapie infected mice (6 and 24 months old mice, 4 in each group) and age matched wt controls were amplified for Snord3A by real time PCR as described. Relative RNA expression levels were normalized in reference to UBC. Relative Snord3A expression level in scrapie infected mice is indicated by fold change versus age-matched controls. <u>Insert</u>: Immunoblotting of PrP^Sc in brains of infected mice (2 young, two old). (** P value <0.001).</p

Elevation of Snord3A expression in Tg MHu2M E199K MEFs and in copper treated mice.

<p>Total RNA from brains of TgMHu2ME199K and wild-type mice as described, as well as from designated MEFs were amplified for Snord3A by Real time PCR. Relative RNA expression levels were normalized in reference to UBC and <i>β-actin</i> (Respectively). a: Scheme of accumulation of PrP and MEF survival during copper treatment (as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054433#pone.0054433-Canello2" target="_blank">[32]</a>). b: Snord3A levels in designated MEFs (wt: cells from wt mice; tg: cells from TgMHu2ME199K mice; KO: cells from PrP^0/0 mice. c: Snord3A levels in TgMHu2ME199K and wild-type mice brain after 75 days of copper treatment versus age-matched control (** P value <0.001).</p

Differential gene expression profile of E200KCJD patients and carriers compared with non carriers control.

<p>Differential gene expression profile of E200KCJD patients and carriers compared with non carriers control.</p

Elevation of Snord3aA expression in Tg MHu2M E199K mice brains is disease dependent.

<p>Total RNA extracted from brains of TgMHu2ME199K (tg), PrP ^0/0 (ko) and wt mice, od designated ages were reverse transcribed into cDNA and amplified by Real Time PCR as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054433#s4" target="_blank">Materials and methods</a>. Each group comprised 4–7 mice. Gene expression changes are depicted in relevance to those measured at 3 months old wt mice. Relative expression levels were normalized in reference to UBC. (** P value <0.001).</p

XX Ovarian Dysgenesis Is Caused by a PSMC3IP/HOP2 Mutation that Abolishes Coactivation of Estrogen-Driven Transcription

XX female gonadal dysgenesis (XX-GD) is a rare, genetically heterogeneous disorder characterized by lack of spontaneous pubertal development, primary amenorrhea, uterine hypoplasia, and hypergonadotropic hypogonadism as a result of streak gonads. Most cases are unexplained but thought to be autosomal recessive. We elucidated the genetic basis of XX-GD in a highly consanguineous Palestinian family by using homozygosity mapping and candidate-gene and whole-exome sequencing. Affected females were homozygous for a 3 bp deletion (NM_016556.2, c.600_602del) in the PSMC3IP gene, leading to deletion of a glutamic acid residue (p.Glu201del) in the highly conserved C-terminal acidic domain. Proteasome 26S subunit, ATPase, 3-Interacting Protein (PSMC3IP)/Tat Binding Protein Interacting Protein (TBPIP) is a nuclear, tissue-specific protein with multiple functions. It is critical for meiotic recombination as indicated by the known role of its yeast ortholog, Hop2. Through the C terminus (not present in yeast), PSMC3IP also coactivates ligand-driven transcription mediated by estrogen, androgen, glucocorticoid, progesterone, and thyroid nuclear receptors. In cell lines, the p.Glu201del mutation abolished PSMC3IP activation of estrogen-driven transcription. Impaired estrogenic signaling can lead to ovarian dysgenesis both by affecting the size of the follicular pool created during fetal development and by failing to counteract follicular atresia during puberty. PSMC3IP joins previous genes known to be mutated in XX-GD, the FSH receptor, and BMP15, highlighting the importance of hormonal signaling in ovarian development and maintenance and suggesting a common pathway perturbed in isolated XX-GD. By analogy to other XX-GD genes, PSMC3IP is also a candidate gene for premature ovarian failure, and its role in folliculogenesis should be further investigated