PTOV1 enables the nuclear translocation and mitogenic activity of flotillin-1, a major protein of lipid rafts.
PTOV1 is a mitogenic protein that shuttles between the nucleus and the cytoplasm in a cell cycle-dependent manner. It consists of two homologous domains arranged in tandem that constitute a new class of protein modules. We show here that PTOV1 interacts with the lipid raft protein flotillin-1, with which it copurifies in detergent-insoluble floating fractions. Flotillin-1 colocalized with PTOV1 not only at the plasma membrane but, unexpectedly, also in the nucleus, as demonstrated by immunocytochemistry and subcellular fractionation of endogenous and exogenous flotillin-1. Flotillin-1 entered the nucleus concomitant with PTOV1, shortly before the initiation of the S phase. Protein levels of PTOV1 and flotillin-1 oscillated during the cell cycle, with a peak in S. Depletion of PTOV1 significantly inhibited nuclear localization of flotillin-1, whereas depletion of flotillin-1 did not affect nuclear localization of PTOV1. Depletion of either protein markedly inhibited cell proliferation under basal conditions. Overexpression of PTOV1 or flotillin-1 strongly induced proliferation, which required their localization to the nucleus, and was dependent on the reciprocal protein. These observations suggest that PTOV1 assists flotillin-1 in its translocation to the nucleus and that both proteins are required for cell proliferation.
Santamaría
Anna
A
Unitat de Recerca Biomèdica, Hospital Vall d'Hebrón, Passeig Vall d'Hebrón 119-129, 00835 Barcelona, Spain.
Castellanos
Elisabeth
E
Gómez
Valentí
V
Benedit
Patricia
P
Renau-Piqueras
Jaime
J
Morote
Juan
J
Reventós
Jaume
J
Thomson
Timothy M
TM
Paciucci
Rosanna
R
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D049109:Cell Proliferation; D002478:Cells, Cultured; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing
D014408:Biomarkers, Tumor; D006133:Growth Substances; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; C425183:PTOV1 protein, human; D048868:Adaptor Proteins, Signal Transducing; C106354:flotillins