Anti-VPS4B monoclonal antibody Made to order

Ubiquitylation of membrane proteins triggers their endocytosis at the plasma membrane and subsequent lysosomal degradation through multivesicular bodies (MVBs). A dominant-negative mutant SKD1/Vps4B caused an accumulation of ubiquitylated membrane proteins in MVBs. We have identified 22 membrane proteins whose trafficking is potentially regulated by ubiquitylation. Nine of them, including transferrin receptor (TfR), are indeed ubiquitylated and/or accumulated in MVBs in the cells expressing mutant Vps4. While the recycling route and iron-regulated expression of TfR are well characterized, the mechanism by which the degradation of TfR is regulated is largely unknown. We show that an excess of iron enhances both TfR's ubiquitylation and degradation in lysosomes. Probably, the up-regulated expression of ferritin, an endogenous iron-chelating molecule, attenuated the iron-induced degradation of TfR. Exogenously introduced lysine-less TfR, compared to the wild-type one, showed resistance to the iron-induced ubiquitylation and degradation, when endogenous TfR, which most certainly heterodimerizes with exogenous ones, was depleted with siRNA. These data suggest that the iron-induced ubiquitylation and degradation of TfR along with MVB pathway physiologically plays an important role in iron homeostasis.

It is known that Lassa virus Z protein is sufficient for the release of virus-like particles (VLPs) and that it has two L domains, PTAP and PPPY, in its C terminus. However, little is known about the cellular factor for Lassa virus budding. We examined which cellular factors are used in Lassa virus Z budding. We demonstrated that Lassa Z protein efficiently produces VLPs and uses cellular factors, Vps4A, Vps4B, and Tsg101, in budding, suggesting that Lassa virus budding uses the multivesicular body pathway functionally. Our data may provide a clue to develop an effective antiviral strategy for Lassa virus.