SSSPTA is essential for serine palmitoyltransferase function during development and hematopoiesis

Abstract

Serine palmitoyltransferase complex (SPT) mediates the first and rate-limiting step in the de novo sphingolipid biosynthetic pathway. The larger subunits SPTLC1 and SPTLC2/SPTLC3 together form the catalytic core while a smaller third subunit either SSSPTA or SSSPTB has been shown to increase the catalytic efficiency and provide substrate specificity for the fatty acyl-CoA substrates. The in vivo biological significance of these smaller subunits in mammals is still unknown. Here, using two null mutants, a conditional null for ssSPTa and a null mutant for ssSPTb, we show that SSSPTA is essential for embryogenesis and mediates much of the known functions of the SPT complex in mammalian hematopoiesis. The ssSPTa null mutants are embryonic lethal at E6.5 much like the Sptlc1 and Sptlc2 null alleles. Mx1-Cre induced deletion of ssSPTa leads to lethality and myelopoietic defect. Chimeric and competitive bone marrow transplantation experiments show that the defect in myelopoiesis is accompanied by an expansion of the Lin − Sca1 + c-Kit + stem and progenitor compartment. Progenitor cells that fail to differentiate along the myeloid lineage display evidence of endoplasmic reticulum stress. On the other hand, ssSPTb null mice are homozygous viable, and analyses of the bone marrow cells show no significant difference in the proliferation and differentiation of the adult hematopoietic compartment. SPTLC1 is an obligatory subunit for the SPT function, and because Sptlc1 −/− and ssSPTa −/− mice display similar defects during development and hematopoiesis, we conclude that an SPT complex that includes SSSPTA mediates much of its developmental and hematopoietic functions in a mammalian model.

Sphingolipids in Hematopoiesis: Exploring Their Role in Lineage Commitment

“…On the other hand, the generation of CMPs was significantly depleted, indicating an important role of SPTLC1 in granulopoiesis. Building upon these findings, this group continued their investigation of SPT in hematopoiesis, and they also revealed a role for ssSPTa in myelopoiesis similar to that of SPTLC1 [133]. Specifically, the loss of ssSPTa, but not of ssSPTb, from adult HSCs using Mx-1-Cre mice led to specific impairment of myelopoiesis with increased Lin − Sca1 + c-Kit + stem cells, as well as increased progenitors.…”

“…Specifically, the loss of ssSPTa, but not of ssSPTb, from adult HSCs using Mx-1-Cre mice led to specific impairment of myelopoiesis with increased Lin − Sca1 + c-Kit + stem cells, as well as increased progenitors. [133]. Molecularly, the defect in myelopoiesis was accompanied by evidence of ER stress.…”

Solute Carrier Nucleoside Transporters in Hematopoiesis and Hematological Drug Toxicities: A Perspective

“…The importance of BA-regulated ER stress signaling in HSCs is further supported by seminal works from the Miharada lab which demonstrated that fetal HSCs exhibit low levels of adaptive responses to ER stress that significantly depend on BA chaperone activity for expansion and differentiation [203,204]. As such, the involvement of ER stress signaling in HSC homeostasis is gaining momentum in research, as seen in several new reports on this topic [205][206][207][208][209]. Importantly, the mechanism that allows ENT3 to regulate erythroid pool size introduces a new concept into the understanding of stress-adaptive ER stress signaling in HSCs [207].…”

“…As such, the involvement of ER stress signaling in HSC homeostasis is gaining momentum in research, as seen in several new reports on this topic [205][206][207][208][209]. Importantly, the mechanism that allows ENT3 to regulate erythroid pool size introduces a new concept into the understanding of stress-adaptive ER stress signaling in HSCs [207]. More intriguingly, the ENT3 loss-induced defects in ER stress signaling are not only evident in HSCs but were also observed along the erythroid line of differentiation including hematopoietic progenitors and precursors, which are major targets of anticancer nucleoside analogs.…”

Crystal structure of Sphingobacterium multivorum serine palmitoyltransferase complexed with tris(hydroxymethyl)aminomethane

“…Serine palmitoyltransferase (SPT) is a key enzyme in sphingolipid biosynthesis and catalyzes the pyridoxal 5 0 -phosphate (PLP)-dependent decarboxylative condensation of l-serine (l-Ser) with palmitoyl-CoA (PalCoA) to generate 3-ketodihydrosphingosine (Hanada, 2003). Eukaryotic SPT is a membrane-bound enzyme composed of two core subunits named SPTLC1 and SPTLC2/SPTLC3 (Buede et al, 1991;Nagiec et al, 1994;Hornemann et al, 2006) that are associated with the regulatory components ssSPTa/ssSPTb and ORMDL3 (Parthibane et al, 2021;Chauhan et al, 2016;Han et al, 2009;Gable et al, 2000;Breslow et al, 2010). SPT is essential for cell viability in eukaryotes, and alterations in SPT activity caused by mutations of either the SPTLC1 or the SPTLC2 gene are linked to neurodegenerative diseases such as hereditary sensory and autonomic neuropathy type I (HSAN1) in humans (Bejaoui et al, 2001;Dawkins et al, 2001;Hornemann et al, 2009;Rotthier et al, 2010).…”