DNA AND CELL BIOLOGY Volume 23, Number 3, 2004 © Mary Ann Liebert, Inc. Pp. 175–182 The Ability of Protein Tyrosine Phosphatase SHP-1 to Suppress NFkB Can Be Inhibited by Dominant Negative Mutant of SIRPa NICKOLAY NEZNANOV, 1 LUBOV NEZNANOVA, 1 ROMAN V. KONDRATOV, 2 DONALD M. O’ROURKE, 3 AXEL ULLRICH, 4 and ANDREI V. GUDKOV 2 ABSTRACT In contrast with hematopoietic cells and fibroblasts, which express mainly one form of protein tyrosine phos- phatase (PTP) SHP-1 or SHP-2, epithelial cells like A431, HeLa, and 293 express both forms of PTP. These two PTP regulate NFkB activity differently; SHP-1 inhibits and SHP-2 stimulates NFkB activation. In epi- thelial cells the process of NFkB activation depends on the combination of two PTP activities. The activity of PTP SHP-1 dominates in this tandem according to our data. The signal regulatory protein (SIRPa) is the adapter and the substrate of PTP SHP-1 and SHP-2. We investigated the role of SIRPa and its dominant neg- ative mutant in PTP activities in 293 cells. The overexpression of wild-type SIRPa suppresses the activities of both PTP, but has a stronger effect on PTP SHP-2, especially when this protein is overexpressed in 293 cells. In contrast with wild-type SIRPa, its dominant negative mutant acts predominantly against PTP SHP- 1, and can be detected in the complex with PTP SHP-1. The expression of dominant negative mutant of SIRPa has an effect similar to the expression of dominant negative PTP SHP-1 in the process of NFkB activation. 175 INTRODUCTION P TP SHP-1 (SH-PTP1, PTP1C, PTPN6, hematopoietic cells PTP (Matthews et al ., 1992; Yi et al., 1992) and PTP SHP-2 (SH-PTP2, PTP2C, PTPN11) (Ahmad et al., 1993) form a group of intracellularnontransmembranetyrosinephosphatases containingtwo SH2 domains and one catalyticdomain (Ahmad et al., 1993). SH2 domains direct the association of these PTP with specific phosphotyrosine containing sites on activated growth factor receptors and certain cytoplasmic signaling pro- teins (Pawson and Gish, 1992). PTP SHP-1 and SHP-2 are ac- tive in different signaling processes and provide dephosphory- lation of tyrosines of cell surface receptors (Lechleider et al., 1993), adaptor molecules (Kharitonenkov et al., 1997), and some cytoplasmic proteins in signaling cascades (Pawson, 1995). PTP SHP-1 and SHP-2 are involved in NFkB activation,but their effects on this process are different. PTP SHP-1 is a neg- ative regulator of NFkB activation. The activation of NFkB is higher in the cells from PTP SHP-1 deficient “motheaten” mu- tant mice (Khaled et al., 1998; Massa and Wu, 1998). These animals have a high percentage of early mortality due to dif- ferent inflammatory disorders (Sidman et al., 1984). In contrast with PTP SHP-1, PTP SHP-2 is a positive regulator of NFkB activation. NFkB activation by TNF and IL-1 was suppressed in the fibroblasts from the mice with knockout of both alleles of PTP SHP-2 gene (You et al., 2001). We can predict that the ability of different factors to stimulate NFkB should depend on correlation of activities of these PTP in the cells. The ability of PTP SHP-1 and SHP-2 to regulate NFkB activationmakes these phosphatases an attractive target for the treatment of inflam- mation and cancer. The recruitment and the activation of PTP in signaling re- quire the presence of adapter molecules. In some processes the role of these adapter moleculesplay inhibitoryreceptors,which contain within their cytoplasmic domains tyrosine residues re- 1 Department of Virology and 2 Molecular Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 3 Departments of Neurosurgery and Pathology & Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Penn- sylvania. 4 Department of Molecular Biology, Max-Planck-Institute fur Biochemie, Martinsried, Germany.