SHP‐1 Tyrosine Phosphatase in Human Erythrocytes

Abstract

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.

Sulphate and Chloride-Dependent Potassium Transport in Human Erythrocytes are Affected by Crude Venom from Nematocysts of the JellyfishPelagia noctiluca

“…NEM (0.5-2 mM) was previously shown to activate K-Cl cotransport in human, rabbit and sheep erythrocytes [31,32,33], activate the tetramer-to-dimer transition of spectrin (attributed to a weakened interaction between ankyrin and AE1/Band 3) [34], and alter the activity of protein phosphatase 1 and 2A (serine phosphatases) [35], calpain-1 [36] and the tyrosine phosphatase SHP1 (Src homology phosphatase-1) [37]. Band 3 is mainly phosphorylated at three tyrosine residues (8, 21, and 46) in the cytoplasmic domain [38].…”

Altered phosphorylation of cytoskeleton proteins in sickle red blood cells: The role of protein kinase C, Rac GTPases, and reactive oxygen species

“…RBCs in circulation retain a number of active protein kinases, including protein kinase C (PKC), protein kinase A (PKA), casein kinases I and II, Syk, Lyn, Hck-Fgr, and Fyn, as recently reviewed by Pantaleo et al [19]. Some of the phosphatases identified in RBCs include SHP-1 and SHP-2, which dephosphorylate tyrosine residues in band 3 [20], PTPH1, a tyrosine-phosphatase for protein 4.1R [21], and the protein phosphatases type 1 and type 2A (PP1 and PP2A), which dephosphorylate serine and threonine residues [22]. It appears that in the resting healthy erythrocyte, phosphatase activity exceeds kinase activity as overall protein phosphorylation levels are low [23,24].…”

SHP-1 Arrests Mouse Early Embryo Development through Downregulation of Nanog by Dephosphorylation of STAT3

“…SHP-1 is a 68 kDa protein tyrosine phosphatase comprising two SH2 domains, a tyrosine phosphatase catalytic domain, and a flexible C-terminal domain [24], [28]–[30]. It is an essential regulatory molecule in many signaling pathways involved in differentiation and proliferation [1], [2].…”