Regulation of surface coat exchange by differentiating African trypanosomes.
African trypanosomes (Trypanosoma brucei) have a digenetic lifecycle that alternates between the mammalian bloodstream and the tsetse fly vector. In the bloodstream, replicating long slender parasites transform into non-dividing short stumpy forms. Upon transmission into the fly midgut, short stumpy cells differentiate into actively dividing procyclics. A hallmark of this process is the replacement of the bloodstream-stage surface coat composed of variant surface glycoprotein (VSG) with a new coat composed of procyclin. Pre-existing VSG is shed by a zinc metalloprotease activity (MSP-B) and glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC). We now provide a detailed analysis of the coordinate and inverse regulation of these activities during synchronous differentiation. MSP-B mRNA and protein levels are upregulated during differentiation at the same time as proteolysis whereas GPI-PLC levels decrease. When transcription or translation is inhibited, VSG release is incomplete and a substantial amount of protein stays cell-associated. Both modes of release are still evident under these conditions, but GPI hydrolysis plays a quantitatively minor role during normal differentiation. Nevertheless, GPI biosynthesis shifts early in differentiation from a GPI-PLC sensitive structure to a resistant procyclic-type anchor. Translation inhibition also results in a marked increase in the mRNA levels of both MSP-B and GPI-PLC, consistent with negative regulation by labile protein factors. The relegation of short stumpy surface GPI-PLC to a secondary role in differentiation suggests that it may play a more important role as a virulence factor within the mammalian host.
Department of Biomolecular Chemistry, University of Wisonsin-Madison, 1300 University Avenue, Madison, WI 53706, USA.
Amy E
AE
Gruszynski
Frederick J
FJ
van Deursen
Maria C
MC
Albareda
Alexander
A
Best
Kshitiz
K
Chaudhary
Laura J
LJ
Cliffe
Laura
L
del Rio
Joe Dan
JD
Dunn
Louise
L
Ellis
Krystal J
KJ
Evans
Juliana M
JM
Figueiredo
Nicholas A
NA
Malmquist
Yusuf
Y
Omosun
Jennifer B
JB
Palenchar
Sara
S
Prickett
George A
GA
Punkosdy
Giel
G
van Dooren
Qian
Q
Wang
Anant K
AK
Menon
Keith R
KR
Matthews
James D
JD
Bangs
D000818:Animals; D005786:Gene Expression Regulation; D054800:Glycosylphosphatidylinositol Diacylglycerol-Lyase; D008018:Life Cycle Stages; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D045726:Metalloproteases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics / Q000378:metabolism*
D008562:Membrane Glycoproteins; D015800:Protozoan Proteins; D014643:Variant Surface Glycoproteins, Trypanosoma; C053277:procyclic acidic repetitive protein, Trypanosoma; D045726:Metalloproteases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054800:Glycosylphosphatidylinositol Diacylglycerol-Lyase