Adam Lerner, M.D.
Professor of Medicine and Pathology
B.A. Amherst College
M.D. Yale University
PDE project: PDE4B, a cAMP phosphodiesterase (PDE) is up-regulated in murine thymocytes undergoing apoptosis following in vivo crosslinking of CD3 (EMBO 1996). Given that chronic lymphocytic leukemia cells (CLL) undergo apoptosis following treatment with the non-specific PDE inhibitor theophylline, we tested whether PDE4 might be the physiologic target of theophylline. Inhibition of PDE4 with rolipram reproducibly induces CLL apoptosis (Blood 1998) by a mitochondrial pathway involving BAD and PP2A (Blood 2003). Interestingly, PDE4 inhibitors also activate EPAC, a cAMP-activated Rap1 GDP exchange factor that is not expressed in any other circulating hematopoietic cell (Blood 2004). When activated in the absence of concurrent PKA activation, this pathway is antiapoptotic, suggesting that EPAC may be of pathophysiologic importance in this disease. PDE4 inhibitors confer their most dramatic apoptotic effects in conjunction with glucocorticoids such as hydrocortisone or dexamethasone (see Biochemical Pharmacology 69 (2005) 473–483). PDE4 inhibitor-mediated PKA activation augments glucocorticoid-induced GRE transactivation in primary human B-CLL cells and inhibition of PKA blocks glucocorticoid-mediated apoptosis in CLL. Currently, we are studying the mechanism by which PKA augments glucocorticoid-mediated apoptosis in primary B-CLL cells, as well as the physiologic role of EPAC in CLL biology (see recent review of this field in Biochem. J. (2006) 393, 21–41).
AND-34 project: I cloned AND-34 in the same study of anti-CD3-mediated thymocyte apoptosis described above. AND-34 has an SH2 domain as well as a domain with homology to the cdc25 domain of ras-family GDP-exchange factors (GEFs), a group of proteins that activate ras family members by facilitating release of GDP. AND-34 underwent tyrosine phosphorylation itself and associated with tyrosine phosphorylated proteins following addition of serum or adhesion of cells to fibronectin. We identified one of the proteins associated with AND-34 as p130Cas, a focal adhesion adapter protein (J. Immunol. 1999). We subsequently demonstrated that AND-34 binds to p130Cas through its GEF-like domain (JBC 2000). Despite its carboxy-terminal domain with homology to cdc25, AND-34′s principal biochemical activity is that of acting the Rho subfamily GTPases Rac and Cdc42 (J. Immunol 2003). This activity correlates with AND-34′s ability to induce both cyclin D1 promoter activation and antiestrogen resistance in breast cancer cell lines upon over expression (Cancer Research 2003).
Most recently, we have determined that AND-34 over-expression leads to Rac activation as a result of its ability to activate PI3K. Inhibition of PI3K blocked AND-34-mediated antiestrogen resistance (Mol. Cancer Research 2004) Our current research focuses on the target of AND-34′s SH2 domain and its role in breast cancer and B cell biology.