Murine leukemia virus spreading in mice impaired in the biogenesis of secretory lysosomes and Ca2+-regulated exocytosis.
BACKGROUND
Retroviruses have been observed to bud intracellularly into multivesicular bodies (MVB), in addition to the plasma membrane. Release from MVB is thought to occur by Ca(2+)-regulated fusion with the plasma membrane.


RESULTS
To address the role of the MVB pathway in replication of the murine leukemia virus (MLV) we took advantage of mouse models for the Hermansky-Pudlak syndrome (HPS) and Griscelli syndrome. In humans, these disorders are characterized by hypopigmentation and immunological alterations that are caused by defects in the biogenesis and trafficking of MVBs and other lysosome related organelles. Neonatal mice for these disease models lacking functional AP-3, Rab27A and BLOC factors were infected with Moloney MLV and the spread of virus into bone marrow, spleen and thymus was monitored. We found a moderate reduction in MLV infection levels in most mutant mice, which differed by less than two-fold compared to wild-type mice. In vitro, MLV release form bone-marrow derived macrophages was slightly enhanced. Finally, we found no evidence for a Ca(2+)-regulated release pathway in vitro. Furthermore, MLV replication was only moderately affected in mice lacking Synaptotagmin VII, a Ca(2+)-sensor regulating lysosome fusion with the plasma membrane.


CONCLUSIONS
Given that MLV spreading in mice depends on multiple rounds of replication even moderate reduction of virus release at the cellular level would accumulate and lead to a significant effect over time. Thus our in vivo and in vitro data collectively argue against an essential role for a MVB- and secretory lysosome-mediated pathway in the egress of MLV.
Chan
Wai-Tsing
WT
Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, United States of America.
Sherer
Nathan M
NM
Uchil
Pradeep D
PD
Novak
Edward K
EK
Swank
Richard T
RT
Mothes
Walther
W
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005089:Exocytosis; D022861:Hermanski-Pudlak Syndrome / Q000235:genetics; D006801:Humans; D009052:Leukemia Virus, Murine / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence / Q000379:methods; D012190:Retroviridae / Q000378:metabolism; D050857:Synaptotagmins / Q000378:metabolism; D013577:Syndrome
D050857:Synaptotagmins; D002118:Calcium