Signal transducer and activator of transcription 3 (Stat3) is a cytosolic transcription factor that relates signals from the cell membrane directly to the nucleus where it, in complex with other proteins, initiates the transcription of antiapoptotic and cell cycling genes, e.g., Bcl-x(L) and cyclin D1. In normal cells Stat3 transduces signals from cytokines such as IL-6 and growth factors such as the epidermal growth factor. Stat3 is constitutively activated in a number of human tumors. Antisense and dominant negative gene delivery result in apoptosis and reduced cell growth, thus this protein is an attractive target for anticancer drug design. As part of our research on the design of Src homology 2 (SH2) directed peptidomimetic inhibitors of Stat3, in this paper we describe structure-activity relationship studies that provide information on the nature of peptide-protein interactions of a high-affinity phosphopeptide inhibitor of Stat3 dimerization and DNA binding, Ac-Tyr(PO3H2)-Leu-Pro-Gln-Thr-Val-NH2, peptide 1. There is a hydrophobic surface on the SH2 domain that can accommodate lipophilic groups on the N-terminus. Of the amino acids tested, leucine provided the highest affinity at pY+1 and its main chain NH is involved with a hydrogen bond with Stat3, presumably Ser636. cis-3,4-Methanoproline is optimal as a backbone constraint at pY+2. The side chain amide protons of Gln are required for high-affinity interactions. The C-terminal dipeptide, Thr-Val, can be replaced with groups ranging in size from methyl to benzyl. We synthesized a phosphopeptide incorporating groups that provided increases in affinity at each position. Thus, hydrocinnamoyl-Tyr(PO3H2)-Leu-cis-3,4-methanoPro-Gln-NHBn, 50, was the highest affinity peptide, exhibiting an IC50 of 125 nM versus 290 nM for peptide 1 in a fluorescence polarization assay.

Phosphorylation and dephosphorylation are key events in protein expression and regulation and in signal transduction. Phosphopeptides are very useful reagents for the study of these processes, and have been used to great advantage in the study of phosphatase substrate specificity, SH2 domain ligand specificity, and protein–protein interactions. Furthermore, the advent of cell‐permeable peptide carriers, such as those from the antennapedia homeodomain and the HIV TAT transcription factor, has allowed the study of intracellular events, thus underscoring the utility of these reagents. In this paper we review methods for the synthesis of phosphopeptides with the emphasis on the preparation of phosphoamino acid building blocks. © 2001 John Wiley & Sons, Inc. Biopolymers (Pept Sci) 60: 3–31, 2001

Cloning of the t(14;18) translocation breakpoint resulted in the identification of a new putative oncogene, which mapped to 18q21, termed bcl-2. The t(14;18) resulted in inappropriately high levels of bcl-2 expression in follicular lymphoma. Prospective studies using mice transgenic for a human bcl-2-immunoglobulin minigene, intended to recreate the molecular features of the t(14;18), demonstrated that bcl-2 gene deregulation was oncogenic. Interestingly, overexpression of bcl-2 showed no demonstrable influence on rates of cellular proliferation. Rather, bcl-2 was found to extend cellular viability by blocking apoptosis. Recent studies with other oncogenes and tumor suppressor genes, such as c-myc and p53, have demonstrated that the deregulation of apoptosis may be of general significance in the development of multiple types of cancer and appears to be a critical event during multistep carcinogenesis. The selective induction of apoptosis in tumor cell populations is now being considered in the design of novel therapeutic interventions.

Autoantibodies to GluR3, an AMPA glutamate receptor subtype, may be a cause of chronic unilateral encephalitis (Rasmussen's syndrome). We report a woman with chronic left hemisphere encephalitis whose partial seizures, aphasia, and motor weakness are highly responsive to intermittent steroids and cyclophosphamide. Her serum and CSF were negative for antibodies to GluR3 by both immunoblot and immunocytochemical analysis of cells transfected with GluR3 cDNA, indicating that separate immune-mediated processes may be involved in some cases of chronic encephalitis.

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