Alternative titles; symbols
HGNC Approved Gene Symbol: TSPO
Cytogenetic location: 22q13.2 Genomic coordinates (GRCh38) : 22:43,151,559-43,163,242 (from NCBI)
TSPO has channel-like properties and is primarily located in the outer mitochondrial membrane. It is involved in a variety of functions, including immunologic responses, apoptosis, and steroidogenesis. The proapoptotic function of TSPO appears to involve modulation of the mitochondrial transition pore (MPTP), a channel formed by the voltage-dependent anion channel (VDAC; see 604492) and the adenine nucleotide transporter (ANT; see 103220). In steroidogenesis, TSPO appears to operate as a translocator to transfer cholesterol into mitochondria, where it is converted to pregnenolone (review by Veenman et al., 2007).
Benzodiazepines are psychoactive drugs with sedative, anxiolytic, and anticonvulsant properties. They exert these actions through receptors located in the central nervous system; however, some benzodiazepines also interact with a different type of receptor present mainly in the mitochondrial compartment of peripheral tissues. Riond et al. (1991) found that the peripheral receptor is similar in rat, Chinese hamster, and human. Based on these results, they screened a human cDNA library with oligonucleotide probes derived from the Chinese hamster sequence. One clone contained a full-length representation of human peripheral binding site (PBS) mRNA. The amino acid sequence of human benzodiazepine PBS deduced from the cDNA was 79% identical to that of rat Pbs.
Chang et al. (1992) found that the benzodiazepine receptor expressed in COS-1 cells had remarkably different affinities than did the endogenous human benzodiazepine receptor. They interpreted this finding as indicating that the host cell and/or posttranslational modification had important influences on function of the receptor protein.
Shoukrun et al. (2008) found that knockdown of TSPO with antisense TSPO or small interfering RNA in HT29 human colorectal cancer cells increased the rate of cell proliferation compared with controls and reduced the rate of apoptosis. In contrast, pharmacologic activation of TSPO reduced the tumorigenicity of HT29 xenografts in immunodeficient mice and increased their rate of survival. Shoukrun et al. (2008) noted that their results confirmed previous findings in mouse and rat, and they concluded that TSPO is a proapoptotic factor.
Reviews
Veenman et al. (2007) reviewed the roles of TSPO in immunologic responses, apoptosis, and steroidogenesis. They suggested that the involvement of TSPO in such disparate biologic functions may indicate a multidimensional role for TSPO in the host-defense response to disease and injury.
Using a cloned human PBR cDNA as probe, Lin et al. (1993) cloned the gene, which they found covers 13 kb and is divided into 4 exons, with exon 1 encoding only a short 5-prime untranslated segment.
3-Dimensional Structure
Jaremko et al. (2014) presented the 3-dimensional high-resolution structure of mammalian TSPO reconstituted in detergent micelles in complex with its high-affinity ligand PK11195. The TSPO-PK11195 structure is described by a tight bundle of 5 transmembrane alpha-helices that form a hydrophobic pocket accepting PK11195. Ligand-induced stabilization of the structure of TSPO suggested a molecular mechanism for the stimulation of cholesterol transport into mitochondria.
Using the cDNA of human BZRP as a probe, Riond et al. (1991) localized the BSRP gene to chromosome 22q13.3 by in situ hybridization. Chang et al. (1992) mapped the BZRP gene to chromosome 22 by hybridization to DNA from a somatic cell hybrid mapping panel. With a regional panel for chromosome 22, they localized the gene within band 22q13.31.
Bucan et al. (1993) mapped the mouse Bzrp gene to chromosome 15.
Bucan, M., Gatalica, B., Nolan, P., Chung, A., Leroux, A., Grossman, M. H., Nadeau, J. H., Emanuel, B. S., Budarf, M. Comparative mapping of 9 human chromosome 22q loci in the laboratory mouse. Hum. Molec. Genet. 2: 1245-1252, 1993. [PubMed: 8401507] [Full Text: https://doi.org/10.1093/hmg/2.8.1245]
Chang, Y. J., McCabe, R. T., Rennert, H., Budarf, M. L., Sayegh, R., Emanuel, B. S., Skolnick, P., Strauss, J. F., III. The human 'peripheral-type' benzodiazepine receptor: regional mapping of the gene and characterization of the receptor expressed from cDNA. DNA Cell Biol. 11: 471-480, 1992. [PubMed: 1326278] [Full Text: https://doi.org/10.1089/dna.1992.11.471]
Jaremko, L., Jaremko, M., Giller, K., Becker, S., Zweckstetter, M. Structure of the mitochondrial translocator protein in complex with a diagnostic ligand. Science 343: 1363-1366, 2014. [PubMed: 24653034] [Full Text: https://doi.org/10.1126/science.1248725]
Lin, D., Chang, Y. J., Strauss, J. F., III, Miller, W. L. The human peripheral benzodiazepine receptor gene: cloning and characterization of alternative splicing in normal tissues and in a patient with congenital lipoid adrenal hyperplasia. Genomics 18: 643-650, 1993. [PubMed: 8307574] [Full Text: https://doi.org/10.1016/s0888-7543(05)80367-2]
Riond, J., Mattei, M. G., Kaghad, M., Dumont, X., Guillemot, J. C., Le Fur, G., Caput, D., Ferrara, P. Molecular cloning and chromosomal localization of a human peripheral-type benzodiazepine receptor. Europ. J. Biochem. 195: 305-311, 1991. [PubMed: 1847678] [Full Text: https://doi.org/10.1111/j.1432-1033.1991.tb15707.x]
Shoukrun, R., Veenman, L., Shandalov, Y., Leschiner, S., Spanier, I., Karry, R., Katz, Y., Weisinger, G., Weizman, A., Gavish, M. The 18-kDa translocator protein, formerly known as the peripheral-type benzodiazepine receptor, confers proapoptotic and antineoplastic effects in a human colorectal cancer cell line. Pharmacogenet. Genomics 18: 977-988, 2008. [PubMed: 18806692] [Full Text: https://doi.org/10.1097/FPC.0b013e3283117d52]
Veenman, L., Papadopoulos, V., Gavish, M. Channel-like functions of the 18-kDa translocator protein (TSPO): regulation of apoptosis and steroidogenesis as part of the host-defense response. Curr. Pharm. Des. 13: 2385-2405, 2007. [PubMed: 17692008] [Full Text: https://doi.org/10.2174/138161207781368710]