Nuclear Localization of L-type Glutaminase in Mammalian Brain

Abstract

In mammals, there are two different genes encoding for glutaminase isoforms, named liver (LGA) and kidney (KGA) types. LGA has long been believed to be present only in liver mitochondria from adult animals. However, we have recently reported the presence of LGA mRNA in human brain. We now describe the expression of LGA mRNA in the brain of other mammals (cow, mouse, rabbit, and rat) and in different areas of human brain as assessed by Northern blot analysis. The presence of mRNA encoding for this isoform in rat brain was further confirmed by reverse transcriptase-PCR cloning and sequencing. Although it has been well accepted that glutaminase is a mitochondrial enzyme, using newly generated isoform-specific antibodies, we have found a differential intracellular immunolocalization of both glutaminase isoforms in rat and monkey brain. In both species, KGA protein was present in mitochondria, whereas LGA protein was localized in nuclei. Furthermore, subcellular fractionation and Western blot analysis revealed that brain LGA was enriched in nuclei where it was catalytically active. Nuclear glutaminase exhibited a kinetic behavior that resembles that of the liver-type enzyme with regard to the low phosphate concentration requirement; however, nuclear glutaminase was susceptible to glutamate inhibition, a property that is absent in the rat liver enzyme.

A Tale of Two Glutaminases: Homologous Enzymes with Distinct Roles in Tumorigenesis

“…The N-termini of the GLS variants begin with a 16-residue sequence generally predicted to localize the proteins to the mitochondria, and indeed, there is near predictive and experimental consensus that GLS is localized to this organelle (Table 1 & Table 2) [34][35][36][37][38][39][40][41][42][43][44][45]. To predict GLS localization, we utilized five freely available predictive algorithms, one of which predicted localization based upon the N-terminal sequence only (TargetP) [42], one of which used the whole protein sequence (SCLPred) [44] and the remaining three of which made predictions based on whole-protein genetic ontology (GO) calculations [41,43,45].…”

GLS2 is transcriptionally regulated by p73 and contributes to neuronal differentiation

“…3,4 Although early studies showed that GLS1 is ubiquitously expressed, 2 and that GLS2 is mainly expressed in the liver, 4 more recent observations indicate that the expression pattern is more complex. Indeed, GLS2 has also been detected in brain, 5 pancreas, 6 cancer cells, 7 and cells of the immune system. 8 Both isoforms have been identified in human and mouse brain.…”

“…At the subcellular level, GLS2 localizes to the inner mitochondrial membrane, while in neurons it has been observed in the nucleus. 5 The abundance of a particular glutaminase mRNA species may significantly change depending upon the tissue type and the developmental or metabolic state of the tissue; therefore, each transcript may represent a specific target for different stimuli. However, although GLS distribution has been extensively investigated, the regulation of GLS1/GLS2 expression is poorly understood.…”

Potentiation of excitotoxicity in HIV-1-associated Dementia and the significance of glutaminase

“…There are two loci in humans that yield structurally related but distinct glutaminase enzymes. Liver type glutaminase (LGA) is primarily expressed in periportal hepatocytes, although transcripts have been found in the brain (159). Kidney type glutaminase (KGA) is abundant not only in the kidney, but also the brain, intestine, liver, lymphocytes and various tumors (34).…”

“…Glutaminase is generally localized to the inner membrane of the mitochondria (172)(173)(174); although additional studies have recognized a nuclear population of glutaminase (159,167). Increase in amount, activity or release of glutaminase could facilitate uncontrolled generation of glutamate in the CNS extracellular space.…”