Mark J. Neveu

The CD28 and CTLA-4 Receptors Associate with the Serine/Threonine Phosphatase PP2A

CD28 and CTLA-4 are related members of a family of T lymphocyte cell surface receptors that function to regulate T cell activation. We have found that the cytoplasmic domains of both CTLA-4 and CD28 can associate with members of the PP2A family of serine/threonine phosphatases. The association of PP2A with CD28 was negatively regulated by tyrosine phosphorylation of the CD28 cytoplasmic domain. Inhibition of PP2A activity in Jurkat leukemia T cells by treatment with okadaic acid or by expression of a dominant-negative mutant enhanced T cell activation induced by CD28 engagement. Interactions between cell surface receptors such as CTLA-4 and CD28 and serine/threonine phosphatases may represent a novel mechanism for modulating the intracellular signal transduction pathways associated with cell activation.

Identification of the human cDNA for new survival/evasion peptide (DSEP): Studies in vitro and in vivo of overexpression by neural cells

We identified the human cDNA encoding a peptide that has been partially purified from the secretions of oxidatively stressed neural cell lines, murine adenocarcinoma cells, and group Abeta-hemolytic steptococci. We then genetically modified mouse and human neural cells to overexpress this peptide and found these modified cells to be remarkably hearty, surviving under conditions of severe oxidative stress, in xenocultures when exposed to activated macrophages, and as xenografts in the brain of rats that were not immunosuppressed. The peptide is called DSEP (dee-sep) for diffusible survival evasion peptide. Part of the survival advantage of DSEP overexpressors may be due to their attenuated response to all-trans-retinoic acid, which regulates differentiation and apoptosis of several cell types including neural and immune cells.

Multistage Hepatocarcinogenesis in the Rat as a Basis for Models of Risk Assessment of Carcinogenesis

Although biological processes are, in general, far more complex than chemical and physical phenomena, one goal of biology, toxicology, and pathology is the mathematical-statistical formulation of models that describe the mechanisms of normal and disease processes. However, as pointed out by several scientists (Whittemore, 1978; Moolgavkar, 1986; Alavanja et al., 1987), up to this time no mathematical-statistical model of a biological process has faithfully described all of the particulars of the biological phenomenon under consideration. This is especially true in the field of carcinogenesis (cf. Chu, 1987) where many models have been proposed in the past. With any model, however, its formulation is dependent on the level of knowledge of the biological mechanisms controlling the process, i.e., carcinogenesis. Recent advances in our understanding of the mechanisms of carcinogenesis as a multistage process have allowed, at least potentially, for a closer congruence between models representative of carcinogenesis and their pathogenesis.

Gene Activation and Deactivation during Multistage Hepatocarcinogenesis in the Rat

That the development of most cancer occurs as a result of two or more separate and distinct processes or stages is rapidly becoming more evident as careful studies of carcinogenesis in defined systems take place. In at least five different species of animals, multistage carcinogenic processes have been demonstrated in more than 15 different tissues1. In addition, there is significant epidemiologic evidence that more than a half dozen human cancers exhibit demonstrable stages in their development2. However, there is to date no uniform agreement as to the number and characteristics of distinctive stages or processes in the development of cancer.

Peptides for elucidating the signal tranduction pathways of CTLA-4 and CD28

CTLA-4, transiently expressed on the surface of activated T-cells, binds to antigen presenting cell ligands B7.1 and B7.2 with 100 fold higher affinity than its competitive receptor, CD28. CD28 promotes T-cell activation upon such binding, however, CTLA-4 bound to B7 ligands potently down regulates cytokine production. Upon binding of B7 to either CTLA-4 or CD28, intracellular signal transduction commences via their cytoplasmic tails. The cascade of proteins binding to these cytoplasmic tails and their signal transduction paths are poorly understood beyond initial recruitment of known signal transduction initiators. Peptides, incorporating a biotin tag, emulating these tails were synthesized as monomeric and dimeric constructs varying in states of phosphorylation. These peptides demonstrate functionality by binding to PI3-kinase and SHP-2 phosphatase, which are known to initially bind to these cytoplasmic tails and thought to be initiators of the signal transduction cascades [1]. Peptide characterizations, as demonstrated by Western blotting analysis, show appropriate functionality.