A Functional Nuclear Localization Sequence in the C-terminal Domain of SHP-1

The Src homology 2 domain-containing protein tyrosine phosphatases SHP-1 and SHP-2 play an important role in many intracellular signaling pathways. Both SHP-1 and SHP-2 have been shown to interact with a diverse range of cytosolic and membrane-bound signaling proteins. Generally, SHP-1 and SHP-2 perform opposing roles in signaling processes; SHP-1 acts as a negative regulator of transduction in hemopoietic cells, whereas SHP-2 acts as a positive regulator. Intriguingly, SHP-1 has been proposed to play a positive regulating role in nonhemopoietic cells, although the mechanisms for this are not understood. Here we show that green fluorescent protein-tagged SHP-1 is unexpectedly localized within the nucleus of transfected HEK293 cells. In contrast, the highly related SHP-2 protein is more abundant within the cytoplasm of transfected cells. In accordance with this, endogenous SHP-1 is localized within the nucleus of several other nonhemopoietic cell types, whereas SHP-2 is distributed throughout the cytoplasm. In contrast, SHP-1 is confined to the cytoplasm of hemopoietic cells, with very little nuclear SHP-1 evident. Using chimeric SHP proteins and mutagenesis studies, the nuclear localization signal of SHP-1 was identified within the C-terminal domain of SHP-1 and found to consist of a short cluster of basic amino acids (KRK). Although the KRK motif resembles half of a bipartite nuclear localization signal, it appears to function independently and is absolutely required for nuclear import. Our findings show that SHP-1 and SHP-2 are distinctly localized within nonhemopoietic cells, with the localization of SHP-1 differing dramatically between nonhemopoietic and hemopoietic cell lineages. This implies that SHP-1 nuclear import is a tightly regulated process and indicates that SHP-1 may possess novel nuclear targets. The Src homology 2 domain-containing protein tyrosine phosphatases SHP-1 and SHP-2 play an important role in many intracellular signaling pathways. Both SHP-1 and SHP-2 have been shown to interact with a diverse range of cytosolic and membrane-bound signaling proteins. Generally, SHP-1 and SHP-2 perform opposing roles in signaling processes; SHP-1 acts as a negative regulator of transduction in hemopoietic cells, whereas SHP-2 acts as a positive regulator. Intriguingly, SHP-1 has been proposed to play a positive regulating role in nonhemopoietic cells, although the mechanisms for this are not understood. Here we show that green fluorescent protein-tagged SHP-1 is unexpectedly localized within the nucleus of transfected HEK293 cells. In contrast, the highly related SHP-2 protein is more abundant within the cytoplasm of transfected cells. In accordance with this, endogenous SHP-1 is localized within the nucleus of several other nonhemopoietic cell types, whereas SHP-2 is distributed throughout the cytoplasm. In contrast, SHP-1 is confined to the cytoplasm of hemopoietic cells, with very little nuclear SHP-1 evident. Using chimeric SHP proteins and mutagenesis studies, the nuclear localization signal of SHP-1 was identified within the C-terminal domain of SHP-1 and found to consist of a short cluster of basic amino acids (KRK). Although the KRK motif resembles half of a bipartite nuclear localization signal, it appears to function independently and is absolutely required for nuclear import. Our findings show that SHP-1 and SHP-2 are distinctly localized within nonhemopoietic cells, with the localization of SHP-1 differing dramatically between nonhemopoietic and hemopoietic cell lineages. This implies that SHP-1 nuclear import is a tightly regulated process and indicates that SHP-1 may possess novel nuclear targets. protein-tyrosine phosphatase green fluorescent protein phosphate-buffered saline normal goat serum nuclear localization signal signal transducer and activator of transcription Tyrosine phosphorylation plays a central role in the transduction of signals from the cell surface to the nucleus. Protein-tyrosine phosphatases (PTPs)1 act both as positive and negative regulators of signal transduction (1Neel B.G. Tonks N.K. Curr. Opin. Cell Biol. 1997; 9: 193-204Crossref PubMed Scopus (736) Google Scholar). Numerous PTPs have been identified so far, including the extensively studied SHP-1 (previously known as PTP1C, SHPTP-1, SHP, and HCP) and SHP-2 (previously termed SHPTP-2, Syp, PTP2C, and PTP1D) intracellular proteins (1Neel B.G. Tonks N.K. Curr. Opin. Cell Biol. 1997; 9: 193-204Crossref PubMed Scopus (736) Google Scholar, 2Feng G. Pawson T. Trends Genet. 1994; 10: 54-58Abstract Full Text PDF PubMed Scopus (169) Google Scholar, 3Neel B.G. Semin. Cell Biol. 1993; 4: 419-432Crossref PubMed Scopus (106) Google Scholar). SHP-1 is expressed at high levels in hemopoietic cells and moderately in many other cell types, especially malignant epithelial cells (4Plutzky J. Neel B.G. Rosenberg R.D. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 1123-1127Crossref PubMed Scopus (286) Google Scholar, 5Shen S.-H. Bastien L. Posner B.I. Chretien P. Nature. 1991; 352: 736-739Crossref PubMed Scopus (337) Google Scholar, 6Yi T. Cleveland J.L. Ihle J.N. Mol. Cell. Biol. 1992; 12: 836-846Crossref PubMed Scopus (306) Google Scholar), whereas SHP-2 is more widely distributed. Both proteins are structurally very similar, comprising two tandem Src homology 2 domains at the N terminus, a single central catalytic domain, and a C-terminal domain (7Hof P. Pluskey S. Dhe-Paganon S. Eck M. Shoelson S.E. Cell. 1998; 92: 441-450Abstract Full Text Full Text PDF PubMed Scopus (742) Google Scholar, 8Yang J. Liand X. Niu T. Meng W. Zhao Z. Zhou G.W. J. Biol. Chem. 1998; 273: 28199-28207Abstract Full Text Full Text PDF PubMed Scopus (104) Google Scholar). The Src homology 2 domains recruit SHP-1 and SHP-2 to tyrosine-phosphorylated molecules, enabling dephosphorylation to be performed by the catalytic domain (9Pei D. Wang J. Walsh C.T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 1141-1145Crossref PubMed Scopus (128) Google Scholar). Considering the conserved nature of SHP-1 and SHP-2, it is perplexing that when integrated into signaling pathways, both proteins perform opposing roles. Generally, SHP-1 acts as a negative regulator of signal transduction, terminating signals from a diverse range of signaling molecules, including the epidermal growth factor receptor (10Keilhack H. Tenev T. Nyakatura E. Godovac-Zimmermann J. Nielsen L. Seedorf K. Bohmer F.-D. J. Biol. Chem. 1998; 273: 24839-24846Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar), interleukin 3 receptor (11Yi T. Mui A.L.-F. Krystal G. Ihle J.N. Mol. Cell. Biol. 1993; 13: 7577-7586Crossref PubMed Google Scholar), c-kit (12Yi T. Ihle J.N. Mol. Cell. Biol. 1993; 13: 3350-3358Crossref PubMed Scopus (234) Google Scholar), colony-stimulating factor 1 receptor (13Chen H.E. Chang S. Trub T. Neel B.G. Mol. Cell. Biol. 1996; 16: 3685-3697Crossref PubMed Scopus (181) Google Scholar), B- and T-cell antigen receptors (14Pani G. Kozlowski M. Cambier J.C. Mills G.B. Siminovitch K.A. J. Exp. Med. 1995; 181: 2077-2084Crossref PubMed Scopus (240) Google Scholar, 15Pani G. Fischer K.-D. Rascan I.M. Siminovitch K.A. J. Exp. Med. 1996; 184: 839-852Crossref PubMed Scopus (180) Google Scholar), and the receptor-associated Janus-activated kinases (16Klingmuller U. Lorenz U. Cantley L.C. Neel B.G. Lodish H.F. Cell. 1995; 80: 729-738Abstract Full Text PDF PubMed Scopus (841) Google Scholar, 17Jiao H. Berrada K. Yang W. Tabrizi M. Platanias L.C. Yi T. Mol. Cell. Biol. 1996; 16: 6985-6992Crossref PubMed Scopus (254) Google Scholar, 18Yetter A. Uddin S. Krolewski J.J. Jiao H. Yi T. Platanias L.C. J. Biol. Chem. 1995; 270: 18179-18182Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar). In contrast, SHP-2 plays a positive role in many signaling systems and can act as an adapter protein, linking tyrosine kinases and Grb2 to activate the mitogen-activated protein kinase pathway (19Li W. Nishimura R. Kashishian A. Batzer A.G. Kim W.J.H. Cooper J.A. Schlessinger J. Mol. Cell. Biol. 1994; 14: 509-517Crossref PubMed Google Scholar,20Xiao S. Rose D.W. Sasoaka T. Maegawa H. Burke T.R. Roller P.P. Shoelson S.E. Olefsky J.M. J. Biol. Chem. 1994; 269: 21244-21248Abstract Full Text PDF PubMed Google Scholar). Recent studies show that the role of SHP-1 depends on the cell type (21Su L. Zhao Z. Bouchard P. Banville D. Fischer E.H. Krebs E.G. Shen S.-H. J. Biol. Chem. 1996; 271: 10385-10390Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, 22You M. Zhao Z. J. Biol. Chem. 1997; 272: 23376-23381Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar). SHP-1 has a positive effect on mitogenic signaling in several nonhemopoietic cell types, which concurs with its overexpression in certain tumor cells. Overexpression of a catalytically inactive mutant of SHP-1 in HEK293 cells strongly suppresses mitogen-activated pathways and results in decreased cell growth, DNA synthesis, and the transcription of early response genes (21Su L. Zhao Z. Bouchard P. Banville D. Fischer E.H. Krebs E.G. Shen S.-H. J. Biol. Chem. 1996; 271: 10385-10390Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar). Furthermore, transfection of HeLa cells with inactive SHP-1 reduces the signal transducer and activator of transcription (STAT)-DNA binding induced by interferon γ and epidermal growth factor (22You M. Zhao Z. J. Biol. Chem. 1997; 272: 23376-23381Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar). As yet, the molecular basis for the apparent opposite effects of SHP-1 in different cell systems has yet to be defined, although the phosphatase domain appears to be critical. It is widely assumed that SHP-1 and SHP-2 are cytoplasmic proteins and have similar intracellular distributions. In this paper we demonstrate a novel nuclear localization for SHP-1 in nonhemopoietic cells, whereas SHP-2 is distributed throughout the cytoplasm. We also show that the nuclear import of SHP-1 is dependent on a short region of basic amino acid residues in the C-terminal domain that resembles half of a bipartite nuclear localization sequence. In addition, we show that SHP-1 localization differs between nonhemopoietic and hemopoietic cells, with the SHP-1 protein being present almost entirely within the cytoplasm of hemopoietic cell lines. These results have implications regarding the function of SHP-1 in nonhemopoietic cells. All cell lines were obtained from the American Type Culture Collection and maintained at 37 °C in a humidified 5% CO2 incubator. HEK293, HeLa, and A549 cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, 2 mml-glutamine, 100 units/ml penicillin, and 100 μg of streptomycin (Life Technologies, Inc.). MCF-7 cells were maintained in the same growth medium supplemented with 10 μg/ml bovine insulin (Sigma). HL-60, U-937, and Jurkat cells were grown in RPMI 1640 medium (Life Technologies) supplemented with 10% fetal bovine serum, 2 mml-glutamine, 100 units/ml penicillin, and 100 μg of streptomycin. The day before transfection, 5 × 104 HEK293 cells were seeded per well of a 24-well plate. The medium was exchanged for complete medium lacking antibiotics, and the cells were transfected with 1 μg of plasmid DNA and 1 μl of LipofectAMINE 2000 in OptiMEM (Life Technologies) for 6 h according to the manufacturer's instructions. After a change to complete medium, the cells were grown for a further 24 h before processing for microscopy. Green fluorescent protein (GFP)-tagged SHP-1 and SHP-2 fusion constructs were generated using the strategy of overlapping recombination polymerase chain reaction (23Erlich H.A. PCR Technology. 1st ed. Stockton Press, New York1989Crossref Scopus (217) Google Scholar). Platinum Pfxpolymerase (Life Technologies) was used for all polymerase chain reactions. The SHP-1 coding sequence was amplified using a forward SHP-1 primer containing an XhoI site and a Kozak sequence (5′-ccctcgagcccacatggtgaggtggtttcaccg-3′) and a downstream joining primer (5′-cctcgcccttgctcaccatcttcctcttgagggaaccc-3′). GFP (enhanced GFP; CLONTECH) was amplified using a forward joining primer (5′-gggttccctcaagaggaagatggtgagcaagggcgagg-3′) and a reverse GFP primer containing an XhoI site (5′-ccctcgagttacttgtacagctcgtccat-3′). The two resulting products were mixed, and a secondary polymerase chain reaction was performed using the forward SHP-1 and reverse GFP primers. The product was ligated as an XhoI fragment into the expression vector MSCVpuro (CLONTECH). GFP-tagged SHP-2 was constructed in a similar manner using a forward SHP-2 primer (5′-ccctcgagccaccatgacatcgcggagatggtt-3′), joining primers (5′-cctcgcccttgctcaccattctgaaacttttctgctgttg-3′ and 5′-caacagcagaaaagtttcagaatggtgagcaaggagggcgagg-3′), and a reverse GFP primer. The method of overlapping recombination polymerase chain reaction was used to generate cDNAs encoding chimeric SHP-1/SHP-2 proteins from GFP-tagged SHP-1 and SHP-2 templates. SHP-2/1A, SHP-2/1B, and SHP-2/1C were constructed using the forward SHP-2 primer and reverse GFP primer with joining primers (SHP-2/1A, 5′-gtgcagatcctacctctgaaaggtggtaccatggccacatgtctg-3′ and 5′-catacatgtggccatggtaccacctttcagaggtaggatctgcac-3′; SHP-2/1B, 5′-caaacttctctacagccgaaaagaggggcagcggccagagaacaag-3′ and 5′-cttgttctctggccgctgcccctcttttcggctgtagagaagtttg-3′; and SHP-2/1C, 5′-ctatatggcggtccagcattatattgaaacaactaagaagaagctggaggtcctgcag-3′ and 5′-ctgcaggacctccagcttcttcttagttgtttcaatataatgctggaccgccatatag-3′). SHP-1/2 was constructed using the forward SHP-2 primer and reverse GFP primer with joining primers 5′-catcgcccagttcattgaaaccctacagcgcaggattgaagaag-3′ and cttcttcaatcctgcgctgtagggtttcaatgaactgggcgatg-3′. Each chimeric cDNA was cloned as an XhoI fragment into MSCVpuro. The basic residues in the C-terminal domain of GFP-tagged SHP-1 were mutated to alanines using the QuikChange site-directed mutagenesis kit (Stratagene). Oligonucleotides used were BD1 (5′-cagttcattgaaaccactgcggcggcgctggaggtcctgcagtcg-3′ and 5′-cgactgcaggacctccagcgccgccgcagtggtttcaatgaactg-3′), BD2 (5′-gaacaagagggaggaggcagtggcggcgcagcggtcagcagacaag-3′ and 5′-cttgtctgctgaccgctgcgccgccactgcctcctccctcttgttc-3′), and BD3, (5′gagcaagggttccctcgcggcggcgatggtgagcaagggcg-3′ and 5′cgcccttgctcaccatcgccgccgcgagggaacccttgctc-3′), where underlined nucleotides indicate mismatches. HeLa, A549, and MCF-7 cells were plated onto acid-washed glass coverslips at 50% confluence and incubated overnight. HL-60, U-937, and Jurkat cells were spun onto glass slides at 500 rpm for 5 min using a Cytospin 3 (Shandon). Cells were washed for 5 min in phosphate-buffered saline (PBS) and then fixed in 4% in for After a further in cells were incubated in 10% normal goat serum and for The cells were then incubated at °C with in and Cells were washed for 5 min in 10% and before goat was at a in and for 1 After in 10% and the cells were in and in fluorescent medium HEK293 cells were from the and plated onto slides at a of cells per After 24 the cells were washed in and fixed in 4% in for After a in the cells were in fluorescent medium and and GFP was at using an to a of of the cells were using a and was performed with The were using on a of the intracellular of PTPs an into function and is a of on the intracellular localization of SHP-1 and It is widely that both SHP-1 and SHP-2 are within the with proteins are well The localization of both SHP-1 and SHP-2 was by HEK293 cells with cDNAs encoding SHP protein with a C-terminal GFP SHP-1 was found to be localized within the nucleus of all transfected HEK293 cells In contrast, SHP-2 was distributed throughout the cytoplasm of all transfected cells with little nuclear evident. GFP protein was distributed throughout the cell 1 This nuclear cytoplasmic of GFP-tagged SHP-1 and SHP-2 appears to be for a of nonhemopoietic cells that have been A549, and not the that the nuclear localization of SHP-1 was of the of GFP the localization of endogenous SHP-1 was studied in several nonhemopoietic cell lines. Although SHP-1 is expressed in hemopoietic levels of expression have been in HeLa A549 and MCF-7 cell lines (4Plutzky J. Neel B.G. Rosenberg R.D. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 1123-1127Crossref PubMed Scopus (286) Google Scholar, 6Yi T. Cleveland J.L. Ihle J.N. Mol. Cell. Biol. 1992; 12: 836-846Crossref PubMed Scopus (306) Google Scholar). using an that endogenous SHP-1 is localized within the nucleus of cell This that the overexpression of SHP-1 of GFP to the C-terminal of SHP-1 was an to its Furthermore, of SHP-2 in HeLa cells using an that SHP-2 is localized throughout the cytoplasm 2 These results show that SHP protein has a with endogenous SHP-1 being localized within the nuclear of cells. we to SHP-1 localization differs between nonhemopoietic and hemopoietic cells. SHP-1 has been found to be present in the cytoplasm of cells Z. Shen S.-H. Fischer E.H. Proc. Natl. Acad. Sci. U. S. A. 1994; PubMed Scopus Google and J. Siminovitch K.A. S. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). of SHP-1 in HL-60, and Jurkat T-cell cell lines by that endogenous SHP-1 is present within the cytoplasm and from the nucleus SHP-1 localization differs dramatically between the nonhemopoietic and hemopoietic cell lines The of proteins to the nuclear is proteins an import signal nuclear localization signal to be to the nucleus M. J.A. 1991; PubMed Scopus Google Scholar). the fusion protein is the nuclear SHP-1 and SHP-2 are related proteins and structurally very have sequence at the amino acid with the tandem Src homology 2 domains and catalytic domain the of the region of SHP-1 for nuclear chimeric cDNAs were constructed with a C-terminal GFP expressed in HEK293 cells, the chimeric cDNAs encoding of SHP-2 with the C-terminal of SHP-1 and were found to be localized within the of transfected cells and from This that the C-terminal domain of SHP-1 the region of SHP-2 and the cytoplasmic SHP-2 to the nucleus. it was that the C-terminal domain of SHP-1 the signal sequence for nuclear This was by a cDNA encoding SHP-1 with the C-terminal domain by the region of SHP-2 The resulting protein was to the nucleus and within the of all transfected cells 5 the C-terminal domain of SHP-1 is for the nuclear import of Furthermore, the C-terminal domain acids to GFP the nucleus of transfected HEK293 cells with high that the C-terminal domain was for nuclear C-terminal domain of SHP-1 nuclear import. The localization of GFP-tagged of SHP-1 and SHP-2 is HEK293 cells were transfected with cDNAs encoding chimeric proteins comprising of SHP-1 and SHP-2 and proteins containing of SHP-2 with the C-terminal domain of SHP-1 were into the nucleus protein of SHP-1 with the C-terminal domain by that of SHP-2 was to the nucleus and in the cytoplasm The C-terminal domain of SHP-1 was also to GFP into the nucleus with high domains are well known to function as of the C-terminal domains of SHP-1 and SHP-2 that several basic and are present within SHP-1 not in SHP-2 6 BD1 is similar to the of the antigen BD2 and the bipartite of of two short of basic amino acids by residues 6 domains were for the nuclear import of domain was by the basic residues to of BD1 in a protein that the nucleus of BD2 in an SHP-1 protein that also the nucleus of transfected cells In contrast, of almost nuclear with the mutated SHP-1 protein within the This that of the SHP-1/2 chimeric protein and that the short KRK sequence was for nuclear import. it has been shown that in the basic cluster of the bipartite of have a effect on nuclear with in both required to nuclear the basis of the BD2 and domains of SHP-1 not a bipartite the amino acid sequence resembles bipartite from several nuclear proteins. of the nuclear import of SHP-1 whereas a protein lacking both BD2 and a similar the short KRK motif present at the C-terminal of SHP-1 is absolutely required and appears for nuclear of the C-terminal domain of The localization of GFP-tagged SHP-1 containing of the basic domains within the C-terminal domain is SHP-1 lacking BD1 BD2 nuclear whereas of nuclear import The SHP-1 protein containing in both BD2 and is also from the nucleus We have shown using GFP fusion proteins that SHP-1 is present within the nuclear of HEK293 cells, an that to a of transfected nonhemopoietic cells. In contrast, a GFP fusion of the related protein SHP-2 is localized throughout the cytoplasm. of SHP-1 in several nonhemopoietic cell the performed with GFP-tagged that the of SHP-1 was not by overexpression the of a GFP SHP-1 localized to the nucleus of nonhemopoietic cell lines that are known to of In contrast, endogenous SHP-2 was distributed throughout the cytoplasm in cell Furthermore, the localization of SHP-1 differs dramatically between nonhemopoietic and hemopoietic cells. The HL-60, U-937, and Jurkat cells SHP-1 that was confined within the cytoplasm. we have a novel nuclear import of the SHP-1 protein that appears to be to nonhemopoietic cells. The of chimeric proteins that the C-terminal domain of SHP-1 the signal required for the nuclear of mutagenesis that a short KRK sequence at the of the C-terminal domain was and for SHP-1 nuclear import. of this basic domain the of SHP-1 into the nuclear resulting in the of SHP-1 in the cytoplasm. Generally, are as in the of as by In a bipartite basic region can function independently to proteins to the nucleus. In BD2 and a bipartite of appears to nuclear import and implies that acts independently of Furthermore, of BD2 change to the intracellular of the BD2 and of although a bipartite not to function in this it be for a KRK sequence to nuclear import It be that BD2 and function to the nuclear import of with being the more half of the This is not T-cell is of a that a the bipartite nature of which In the region of the T-cell appears not to function in nuclear import J.A. Fischer E.H. J. Cell Biol. 1995; PubMed Scopus Google Scholar). in a and more both basic of the T-cell were shown to be required for nuclear import with basic region independently to a T. Tonks N.K. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). it the of SHP-1 is with further The of SHP-1 nuclear import is not The in SHP-1 between hemopoietic and nonhemopoietic cells implies that the of SHP-1 is in cell In hemopoietic cells, SHP-1 be from the nucleus the C-terminal be for SHP-1 to in the cytoplasm. This be by phosphorylation of amino acid residues within to the by of the by the other of SHP-1 may the region of the encoding the as two generated by to the nucleus and the other to the of the of a of residues J.A. Fischer E.H. J. Cell Biol. 1995; PubMed Scopus Google Scholar). other PTPs in two to intracellular including J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google and S. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). of the SHP-1 has been which the protein which differs from SHP-1 in its C-terminal J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The not possess the domain shown to nuclear import. This the of of the SHP-1 SHP-1 which in SHP-1 function by SHP-1 to at the used in studies was to the C-terminal domain of the protein and SHP-1 the localization of endogenous SHP-1 proteins in hemopoietic and nonhemopoietic cells is more to be to of the nuclear The import of SHP-1 into the nucleus of nonhemopoietic cells may as a by which SHP-1 function is SHP-1 be localized within the nucleus to with cytoplasmic signaling be nuclear It has been that SHP-1 can act as a positive regulator of cell signaling in nonhemopoietic HEK293 and HeLa cells. It was that this be to the dephosphorylation of tyrosine residues that have signaling roles. Here we show that in cell types, SHP-1 is present within the nucleus. Furthermore, we have that SHP-1 is from the nucleus of hemopoietic cell the that SHP-1 localization has been shown to be different within cell it be that SHP-1 its positive role by nuclear tyrosine-phosphorylated proteins. SHP-1 is in a of malignant nonhemopoietic cells, of nuclear SHP-1 dephosphorylation is in the role of SHP-1 in nuclear tyrosine-phosphorylated proteins have been for nuclear PTPs are the which are by tyrosine phosphorylation and to the nucleus 1997; PubMed Scopus Google Scholar). The tyrosine dephosphorylation that has been localized to the as yet the have not been identified M. J. 1996; PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). This a role for SHP-1 in regulating to novel nuclear of SHP-1 are