Visit our Expo - Redox and Inflammation signaling 2012

V. Phosphatases as key cell signaling intermediates Poster V, 1
SHP-1 tyrosine phosphatase in human erythrocytes.
Bragadin M.1, Clari G.2, Ion Popa F.2, Bordin L.2
1 Dept. of Environmental Sciences, Ca’ Foscari University of Venice, Calle Larga
S.Marta Dorsoduro 2137, Venice, Italy; e-mail: bragadin@unive.it
2 Dept. of Biological Chemistry, University of Padua, Viale G. Colombo 3, 35121 Padua,
Italy; e-mail: giulio.clari@unipd.it ; luciana.bordin@unipd.it
SHP-1 is a SH2-domain containing protein Tyr-phosphatase expressed in hematopoietic cell
lines, which is hypothesized to play a largely negative role in signal transduction. In human
erytrocytes, the phospho-Tyr level of proteins, mainly transmembrane band 3 protein, 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 erytrocyte
membrane reorganization.
We demonstrate that, in human red blood cells, SHP-1 is present in membranes from resting
cells, but in 5 percent of the protein amount. Interstingly, this amount increases up to
threefold following NEM treatement 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, since it is not mediated by the SH2-P-tyr recruiment
mechanism, and localizes into the cytoskeletal compartment. Band 3 is the target of SHP-1,
which dephosphorylates tyrosines located in acidic sequences such as Tyr 8,21 and 904.
All together, these findings support the idea that, in human erytrocytes, the normal level of
Tyr-phosphorylation of membrane protein, mainly band 3, must be down regulated. We
hypothesize that the simultaneous 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.
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