Principal Investigator: Dr François FOULQUIER
Grant Title: TMEM165, a new key player in Golgi glycosylation and skeletal
development.
Abstract:
Congenital Disorders of Glycosylation (CDG) are a rapidly growing diseasefamily due to genetic defects of protein and lipid glycosylation. In 2012, wereported a novel disorder in this group namely TMEM165-CDG (OMIMentry #614727). These patients present a peculiar phenotype including
major skeletal dysplasia and hyposialylation and hypogalactosylation of Nglycosylproteins. TMEM165 is a transmembrane protein of 324 aminoacids belonging to a well conserved but uncharacterized family ofmembrane proteins named UPF0016 (Uncharacterized Protein Family0016; Pfam PF01169). Extremely conserved in the eukaryotic reign, wewanted to investigate the molecular mechanisms by which TMEM165 deficiencies lead to
Golgi glycosylation abnormalities is enigmatic.
As GDT1 is the ortholog of TMEM165 in yeast, both gdt1Δ null mutant yeasts and TMEM165
depleted cells were used. Strong galactosylation defects on N-glycoproteins were observed inTMEM165 deficient cells. We highlighted thatTMEM165∆ TMEM165
the observed Golgi glycosylation defects due toGdt1p/TMEM165 deficiency result in fact from
Ca2+/Mn2+Ca2+/Mn2+Mn2+
CytosolGolgi manganese homeostasis defect (figure 1).
We discovered that in both yeasts andmammalian Gdt1p/TMEM165 deficient cells,
Ca2+Mn2+ supplementation could restore a normal
[Mn ]
Golgi
glycosylation. We also showed that the GPP130[Mn2+]
Mn2+ sensitivity was altered in TMEM165
UDP-GalUDP-Galdepleted cells. To go deeper in the molecularmechanisms, we investigated the sensitivity ofGalactosyl
TMEM165 for Mn2+. When exposed to highGalactosyltransferase
transferase
Mn2+ concentrations, we demonstrated that
Figure 1: Schematic representation of the impact of TMEM165 was degraded into lysosomes.
TMEM165 deficiency on Golgi Mn2+ homeostasis andRemarkably, the variant p.E108G recently
N-glycosylation defects.
identified in a novel TMEM165-CDG patient,
was found to be insensitive to Mn2+ supplementation. Moreover, this mutation abolished thefunction of TMEM165, suggesting that a transport function may be necessary for its regulation.
Altogether this grant allowed us to identify the Golgi protein TMEM165 as a novel cytosolic
Mn2+ sensor in mammalian cells and pointed the crucial importance of the cytosolical ELGDK
motif in both Mn2+ sensitivity and function. Moreover, we demonstrated that the observed
Golgi glycosylation deficiencies in Gdt1p/TMEM165 deficient cells result from a defective
Golgi Mn2+ homeostasis then providing novel insights into the mechanism of thegalactosylation defect observed in TMEM165-deficient cells. These findings also support thepotential use of therapeutic trials of Mn2+ in TMEM165 deficient patients.
ATPTMEM165

SPCA1ADP+PiATP

ADP+Pi

SPCA12+

1_ Potelle S, Morelle W, Dulary E, Duvet S, Vicogne D, Spriet C, Krzewinski-Recchi MA, Morsomme P, Jaeken J, MatthijsG, De Bettignies G, Foulquier F. (2016) Glycosylation abnormalities in Gdt1p/TMEM165 deficient cells result from a defectin Golgi manganese homeostasis. Hum Mol Genet. 25, 1489-500.
2_ Potelle S, Dulary E, Climer L, Duvet S, Morelle W, Vicogne D, Spriet C, Krzewinski-Recchi MA, Peanne R, De Bettignies
G, Matthijs G, Marquardt T, Lupashin V, Foulquier F. (2016) Characterization of TMEM165 as a novel Golgi manganesesensitive protein involved in Congenital Disorders of Glycosylation. Submitted to Hum Mol Genet.