The nontransmembrane tyrosine phosphatase PTP-1B localizes to the endoplasmic reticulum via its 35 amino acid C-terminal sequence.
We report the first intracellular characterization of an endogenous nontransmembrane protein tyrosine phosphatase (PTP). Using affinity-purified polyclonal antibodies, we have identified PTP-1B as a 50 kd serine phosphoprotein in immunoprecipitation and immunoblotting assays. Surprisingly, indirect immunofluorescence experiments indicate that PTP-1B is localized predominantly in the endoplasmic reticulum (ER). Subcellular fractionation is consistent with this localization and establishes that PTP-1B is tightly associated with microsomal membranes, with its phosphatase domain oriented towards the cytoplasm. The C-terminal 35 amino acids of PTP-1B are both necessary and sufficient for targeting to the ER. The finding of a tyrosine phosphatase on the ER suggests new possibilities for cellular events controlled by tyrosine phosphorylation.
Frangioni
J V
JV
Molecular Medicine Unit, Beth Israel Hospital, Boston, Massachusetts 02215.
Beahm
P H
PH
Shifrin
V
V
Jost
C A
CA
Neel
B G
BG
D000818:Animals; D000906:Antibodies / Q000302:isolation & purification; D001483:Base Sequence; D002458:Cell Fractionation; D002460:Cell Line; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D006367:HeLa Cells / Q000737:chemistry; D006801:Humans; D015151:Immunoblotting; D008565:Membrane Proteins / Q000032:analysis*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010957:Plasmids; D011233:Precipitin Tests; D021382:Protein Sorting Signals / Q000032:analysis*; D017027:Protein Tyrosine Phosphatases / Q000032:analysis* / Q000235:genetics / Q000276:immunology; D011817:Rabbits
D000906:Antibodies; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D017027:Protein Tyrosine Phosphatases