Sphingosine kinase 2 regulates protein ubiquitination networks in neurons.

Two sphingosine kinase isoforms, sphingosine kinase 1 (SPHK1) and sphingosine kinase 2 (SPHK2), synthesize the lipid sphingosine-1-phosphate (S1P) by phosphorylating sphingosine. SPHK1 is a cytoplasmic kinase, and SPHK2 is localized to the nucleus and other organelles. In the cytoplasm, the SPHK1/S1P pathway modulates autophagy and protein ubiquitination, among other processes. In the nucleus, the SPHK2/S1P pathway regulates transcription. Here, we hypothesized that the SPHK2/S1P pathway governs protein ubiquitination in neurons. We found that ectopic expression of SPHK2 increases ubiquitinated substrate levels in cultured neurons and pharmacologically inhibiting SPHK2 decreases protein ubiquitination. With mass spectrometry, we discovered that inhibiting SPHK2 affects lipid and synaptic protein networks as well as a ubiquitin-dependent protein network. Several ubiquitin-conjugating and hydrolyzing proteins, such as the E3 ubiquitin-protein ligases HUWE1 and TRIP12, the E2 ubiquitin-conjugating enzyme UBE2Z, and the ubiquitin-specific proteases USP15 and USP30, were downregulated by SPHK2 inhibition. Using RNA sequencing, we found that inhibiting SPHK2 altered lipid and neuron-specific gene networks, among others. Genes that encode the corresponding proteins from the ubiquitin-dependent protein network that we discovered with mass spectrometry were not affected by inhibiting SPHK2, indicating that the SPHK2/S1P pathway regulates ubiquitination at the protein level. We also show that both SPHK2 and HUWE1 were upregulated in the striatum of a mouse model of Huntington's disease, the BACHD mice, indicating that our findings are relevant to neurodegenerative diseases. Our results identify SPHK2/S1P as a novel regulator of protein ubiquitination networks in neurons and provide a new target for developing therapies for neurodegenerative diseases.

Diaz Escarcega R ，Murambadoro K ，Valencia R ，Moruno-Manchon JF ，Furr Stimming EE ，Jung SY ，Tsvetkov AS ... -  《-》

Regulation and function of sphingosine kinase 2 in diseases.

Song DD ，Zhou JH ，Sheng R 《-》

Sphingosine kinase 2 and sphingosine-1-phosphate promotes mitochondrial function in dopaminergic neurons of mouse model of Parkinson's disease and in MPP+ -treated MN9D cells in vitro.

Dysregulation of sphingolipid metabolism has been shown to trigger the pathophysiology of many neurodegenerative disorders. The present study focuses on the role of one of the two sphingosine kinases, Sphk2 and its metabolite sphingosine-1-phosphate (S1P) signaling in Parkinson's disease (PD). Our study indicated a marked down regulation of Sphk2 expression in the substantia nigra region of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model and in the cellular PD model. Localization studies indicated that Sphk2 was predominantly present in mitochondria, proposing for its potential role in mitochondrial functions. Since mitochondrial dysfunction has been described to be the major pathological event in PD, the present study focused on the role of Sphk2/S1P signaling in promoting mitochondrial functions in the MPTP-induced mouse model of PD and in 1-methyl-4 phenylpyridinium (MPP(+))-treated MN9D cells. Our study demonstrated that inhibition of Sphk2 decreased the expression of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and its downstream targets nuclear respiratory factor 1 (NRF-1) and mitochondrial transcription factor A (TFAM) which are the key genes regulating mitochondrial function. In addition, there was also a significant reduction in the total cellular adenosine triphosphate (ATP) and superoxide dismutase 2 (SOD 2) with an associated increase in levels of reactive oxygen species (ROS) in the absence of Sphk2. Interestingly, it was found that treating the cells with exogenous S1P along with MPP(+) exerted a neuroprotective effect by activation of p-CREB, PGC-1α and NRF-1 in the MN9D cells. Moreover, the level of ATP was unaffected in the MPP(+)-treated cells in the presence of S1P. It was also observed that levels of ROS were significantly decreased in the MPP(+)-treated cells in the presence of exogenous S1P. Our study also demonstrated that S1P exerted its protective effect through the S1P1 receptor. Taken together, these results show that Sphk2/S1P has an important role to play in the survival of the dopaminergic neurons, in the pathogenesis of PD.

Sivasubramanian M ，Kanagaraj N ，Dheen ST ，Tay SS ... -  《-》

Loss of sphingosine kinase 1/S1P signaling impairs cell growth and survival of neurons and progenitor cells in the developing sensory ganglia.

Meng H ，Yuan Y ，Lee VM 《PLoS One》

Sphingosine-1-phosphate is a missing cofactor for the E3 ubiquitin ligase TRAF2.

Alvarez SE ，Harikumar KB ，Hait NC ，Allegood J ，Strub GM ，Kim EY ，Maceyka M ，Jiang H ，Luo C ，Kordula T ，Milstien S ，Spiegel S ... -  《-》