SHP-1 tyrosine phosphatase in human erythrocytes.
SHP-1 is a SH2-domain containing protein Tyr-phosphatase expressed in hematopoietic cell lines, which is hypothesized to play a negative role in signal transduction. In human erythrocytes, the phospho-Tyr level of proteins, mainly transmembrane band 3, is closely controlled by the antithetic activity of Tyr-protein kinases and phosphatases, resulting in a dephosphorylated state. Only after particular stimuli, as with oxidizing agents, diamide or pervanadate, or thiol alkylating compound, N-ethyl maleimide (NEM), Tyr-phosphorylation of band 3 can be triggered, inhibiting Tyr-phosphatase action and inducing erythrocyte membrane reorganization. We demonstrate that, in human erythrocytes, SHP-1 is present in membranes from resting cells, but in 5% of the protein amount. Interestingly, this amount increases up to threefold following NEM treatment of intact cells, whereas diamide and pervanadate do not alter the normal protein location. In addition, SHP-1 translocation from cytosol to membrane is not affected by band 3 P-Tyr level, because it is not mediated by the SH2-P-Tyr recruitment mechanism, and localizes into the cytoskeletal compartment. Band 3 is the target of SHP-1, which dephosphorylates Tyr 8, 21, and 904. These findings support the idea that, in human erythrocytes, the normal level of Tyr-phosphorylation of membrane protein, mainly band 3, must be downregulated. We hypothesize that the presence of both SHP-2 and SHP-1 ensures band 3 dephosphorylation in different conditions: SHP-2, through interaction of its SH2 domain/s to P-Tyr protein, is regulated by the band 3 Tyr-phosphorylation level; SHP-1 may be involved by simple membrane rearrangement.
Bragadin
Marcantonio
M
Dipartimento di Scienze Ambientali, Dorsoduro 2137, University of Padova, 30123 Venezia, Italy. bragadin@unive.it
Ion-Popa
Florina
F
Clari
Giulio
G
Bordin
Luciana
L
D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D021381:Protein Transport / Q000502:physiology; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000097:blood* / Q000502:physiology
D001457:Anion Exchange Protein 1, Erythrocyte; C454201:SLC4A1 protein, human; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6