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J. Exp. Med.,
Volume 187, Number 4, February 16, 1998 547-560
By

From the * Department of Medicine, Division of Rheumatology, Immunology, and Allergy, Brigham & Women's Hospital, Boston, Massachusetts 02115; and the Proteins subject to proteolysis or phosphorylation during apoptosis are commonly precipitated
by autoantibodies found in the serum of patients with systemic lupus erythematosus (SLE). We screened a panel of murine monoclonal and human monospecific sera reactive with known autoantigens for their ability to selectively precipitate phosphoproteins from apoptotic Jurkat T
cell lysates. Sera known to recognize the U1-small nuclear ribonucleoprotein (snRNP) complex (confirmed by their ability to precipitate U1-snRNA) selectively precipitated a phosphoprotein complex (pp54, pp42, pp34, and pp23) from apoptotic lysates. Monoclonal antibodies reactive with U1-snRNP proteins precipitated the same phosphoprotein complex from apoptotic lysates. The phosphorylation and/or recruitment of these proteins to the U1-snRNP
complex is induced by multiple apoptotic stimuli (e.g., Fas ligation, gamma irradiation, or UV irradiation), and is blocked by overexpression of bcl-2. The U1-snRNP-associated phosphoprotein
complex is immunoprecipitated by monoclonal antibodies reactive with serine/arginine (SR)
proteins that comprise a structurally related family of splicing factors. The association of phosphorylated SR proteins with the U1-snRNP complex in cells undergoing apoptosis suggests a
mechanism for regulation of alternative splicing of apoptotic effector molecules.
Department of Biochemistry, University
of Nijmegen, 6500 HB Nijmegen, The Netherlands
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