PK11195 Effect on Steroidogenesis Is Not Mediated Through the Translocator Protein (TSPO)

Tu, Lan N.; Zhao, Amy H.; Stocco, Douglas M.; Selvaraj, Vimal

doi:10.1210/en.2014-1707

Cited by 77 publications

(88 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This result was again inconsistent with another early report that monoallelic disruption of TSPO in the R2C Leydig cell line obliterated its steroidogenic potential and caused phenotypic abnormality [7]. However, changes in phenotype or issues with viability were not observed in three independent clones of the MA-10:TspoD/D cells examined in the recent study [47], suggesting that TSPO deletion does not affect essential cellular functions. Moreover, when MA-10:TspoD/D cell clones were used to examine the steroidogenic ability of the TSPO-binding chemical PK11195, both control and TSPO-deficient cells showed identical increases in steroid hormone production [47].…”

Section: Box 2 the Mptcontrasting

confidence: 88%

“…However, changes in phenotype or issues with viability were not observed in three independent clones of the MA-10:TspoD/D cells examined in the recent study [47], suggesting that TSPO deletion does not affect essential cellular functions. Moreover, when MA-10:TspoD/D cell clones were used to examine the steroidogenic ability of the TSPO-binding chemical PK11195, both control and TSPO-deficient cells showed identical increases in steroid hormone production [47]. This finding indicated that the effect of PK11195 on steroidogenesis in MA-10 cells is not mediated through TSPO, suggesting that previous studies reporting the pharmacological link between TSPO and steroidogenesis in this cell line and at the same range of concentrations [5,6] were probably describing off-target effects.…”

Section: Box 2 the Mptmentioning

confidence: 72%

“…Another recent study demonstrated that complete disruption of TSPO in the MA-10 cell line (MA-10:TspoD/D) using CRISPR/Cas9-mediated mutagenesis did not have any effect on the viability of the cells or steroidogenesis [47]. This result was again inconsistent with another early report that monoallelic disruption of TSPO in the R2C Leydig cell line obliterated its steroidogenic potential and caused phenotypic abnormality [7].…”

Section: Box 2 the Mptmentioning

confidence: 82%

See 2 more Smart Citations

The changing landscape in translocator protein (TSPO) function

Selvaraj

Stocco

2015

Trends in Endocrinology & Metabolism

Self Cite

105

View full text Add to dashboard Cite

Translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), is an outer mitochondrial membrane protein. TSPO has been shown to cooperate with steroidogenic acute regulatory protein (StAR) and function in the transport of cholesterol into mitochondria. TSPO has also been considered as a structural component of the mitochondrial permeability transition pore (MPTP). However, recent advances have changed these views of TSPO's functions and have prompted a re-evaluation of established concepts. This review summarizes the history of TSPO, key elements of the debate, and functional experiments that have changed our understanding. Moving forward, we examine how this fundamental change impacts our understanding of TSPO and affects the future of TSPO as a therapeutic and diagnostic target.

show abstract

Section: Box 2 the Mptcontrasting

confidence: 88%

Section: Box 2 the Mptmentioning

confidence: 72%

Section: Box 2 the Mptmentioning

confidence: 82%

See 1 more Smart Citation

The changing landscape in translocator protein (TSPO) function

Selvaraj

Stocco

2015

Trends in Endocrinology & Metabolism

Self Cite

105

View full text Add to dashboard Cite

show abstract

“…The cells were passaged once and frozen for use in experiments. Generation and culture of TSPO deleted MA-10 cells (MA-10:Tspo ⌬/⌬ cells) has been previously described (8). Human colon cancer cell lines were obtained from ATCC and cultured using recommended methods.…”

Section: Tspomentioning

confidence: 99%

Mitochondrial Translocator Protein (TSPO) Function Is Not Essential for Heme Biosynthesis

Zhao

Mukai

et al. 2016

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

Function of the mammalian translocator protein (TSPO; previously known as the peripheral benzodiazepine receptor) remains unclear because its presumed role in steroidogenesis and mitochondrial permeability transition established using pharmacological methods has been refuted in recent genetic studies. Protoporphyrin IX (PPIX) is considered a conserved endogenous ligand for TSPO. In bacteria, TSPO was identified to regulate tetrapyrrole metabolism and chemical catalysis of PPIX in the presence of light, and in vertebrates, TSPO function has been linked to porphyrin transport and heme biosynthesis. Positive correlation between high TSPO expression in cancer cells and susceptibility to photodynamic therapy based on their increased ability to convert the precursor 5-aminolevulinic acid (ALA) to PPIX appeared to reinforce this mechanism. In this study, we used TSPO knock-out (Tspo ؊/؊ ) mice, primary cells, and different tumor cell lines to examine the role of TSPO in erythropoiesis, heme levels, PPIX biosynthesis, phototoxic cell death, and mitochondrial bioenergetic homeostasis. In contrast to expectations, our results demonstrate that TSPO deficiency does not adversely affect erythropoiesis, heme biosynthesis, bioconversion of ALA to PPIX, and porphyrin-mediated phototoxic cell death. TSPO expression levels in cancer cells do not correlate with their ability to convert ALA to PPIX. In fibroblasts, we observed that TSPO deficiency decreased the oxygen consumption rate and mitochondrial membrane potential (⌬⌿m) indicative of a cellular metabolic shift, without a negative impact on porphyrin biosynthetic capability. Based on these findings, we conclude that mammalian TSPO does not have a critical physiological function related to PPIX and heme biosynthesis.Mammalian translocator protein (TSPO), 2 previously known as the peripheral benzodiazepine receptor (1), is a highly conserved protein enriched in the outer mitochondrial membrane (2). Despite extensive efforts to characterize TSPO, its precise physiological function remains elusive (3, 4). High levels of TSPO expression in steroidogenic cells, its localization to the outer mitochondrial membrane, and increased steroid production upon pharmacological binding led to the primary prospective model that TSPO was a mitochondrial cholesterol transporter essential for steroidogenesis (5). In recent studies using precise genetic tools, we and others have systematically refuted the involvement of TSPO in this process (6 -10). Similarly, copurification of TSPO with putative members of the mitochondrial permeability transition pore (MPTP) (11) and effects mediated by TSPO binding drugs on modulating apoptosis (12, 13) resulted in a secondary model that TSPO was associated with MPTP function and cell death (14). Again, recent discovery of the molecular identity of MPTP (15) Binding of porphyrins to TSPO has been a consistent property reported in bacteria (18), plants (19), and animals (17). In Rhodobacter sphaeroides, TSPO was found localized to the outer membrane (18) and pl...

show abstract

“…Furthermore, in some cases, as reported for etifoxine on frog hypothalamic explants [93], the increase in steroidogenesis produced by TSPO ligand may be mediated by TSPO independent mechanisms [97].…”

Section: Tspo and The Control Of Neuroactive Steroid Levelsmentioning

confidence: 83%