Sm. Bradykalnay et al., HOMOPHILIC BINDING OF PTP-MU, A RECEPTOR-TYPE PROTEIN-TYROSINE-PHOSPHATASE, CAN MEDIATE CELL-CELL AGGREGATION, The Journal of cell biology, 122(4), 1993, pp. 961-972
The receptor-like protein tyrosine phosphatase, PTPmu, displays struct
ural similarity to cell-cell adhesion molecules of the immunoglobulin
superfamily. We have investigated the ability of human PTPmu to functi
on in such a capacity. Expression of PTPmu, with or without the PTPase
domains, by recombinant baculovirus infection of Sf9 cells induced th
eir aggregation. However, neither a chimeric form of PTPmu, containing
the extracellular and transmembrane segments of the EGF receptor and
the intracellular segment of PTPmu, nor the intracellular segment of P
TPmu expressed as a soluble protein induced aggregation. PTPmu mediate
s aggregation via a homophilic mechanism, as judged by lack of incorpo
ration of uninfected Sf9 cells into aggregates of PTPmu-expressing cel
ls. Homophilic binding has been demonstrated between PTPmu-coated fluo
rescent beads (Covaspheres) and endogenously expressed PTPmu on MvLu c
ells. Additionally the PTPmu-coated beads specifically bound to a bact
erially expressed glutathione-S-transferase fusion protein containing
the extracellular segment of PTPmu (GST/PTPmu) adsorbed to petri dishe
s. Covaspheres coated with the GST/PTPmu fusion protein aggregated in
vitro and also bound to PTPmu expressed endogenously on MvLu cells. Th
ese results suggest that the ligand for this transmembrane PTPase is a
nother PTPmu molecule on an adjacent cell. Thus homophilic binding int
eractions may be an important component of the function of PTPmu in vi
vo.