Kenneth B. Marcu Professor
Departments of Biochemistry and Cell Biology, Microbiology & Pathology
PhD, SUNY @ Stony Brook (1975)
Gene function and regulation in innate and adaptive immunity and neoplasia
The research interests of my laboratory are: (1) the regulation and mechanisms of action of the inhibitor of NF-kB kinase (IKK) complex, which is essential for the activation of the NF-kB transcription factor family (pivotal regulators of stress-like responses, innate and adaptive immunity and the survival of normal and malignant cells); (2) the molecular basis of immunoglobulin heavy chain (Igh) class switch recombination (CSR) in adpaptive immune responses and the mechanisms of action of the 'Activated Induced Deaminase' (AID) protein in CSR and Ig gene somatic hypermutation (SHM).
NF-kB/Rel transcription factors are nuclear regulators of gene expression programs, which orchestrate a host of cellular stress-like responses. In most normal cells, NF-kBs are tethered to their IkB inhibitors and only become transiently activated in response to a variety of extracellular stress-like stimuli including viral and bacterial infections, oxidative and DNA damaging agents, hyperosmotic shock, chemotherapeutics, pro-inflammatory and survival cytokines. The universal mechanism for activating cytoplasmically dormant NF-k B/Rel transcription factors requires that their IkB inhibitors first be phosphorylated by cellular kinases, which targets them for ubiquitination and subsequent destruction by the Proteosome complex. The NF-kB inducing IKK (IkB Kinase) signalsome complex is the final receiver and integrator of the stress-like responses culminating in NF-kB activation. The IKKs consist of two serine/threonine kinases (IKKa and IKKb) and a con-catalytic regulatory/docking protein (NEMO/IKKg). In contrast to this paradigm in most physiologically normal cells, the IKKs and therefore NF-kBs are constitutively activated in a variety of malignant, cancerous cells in the absence of extracellular NF-kB activating stimuli. Malignant cells acquire resistance to oncoprotein induced stress-like stimuli that normally cause senescence or programmed cell death, in part because constitutive NF-kB activation ensures the expression of a variety of survival factors. Thus, inhibition of IKK activity should provide a specific way of dampening the debilitating effects of chronic inflammatory and immune-like reactions commonly observed in a variety of human maladies including arthritis, septic shock, asthma and autoimmune diseases and could also antagonize malignant progression. We are engaged in a variety of projects on the NF-kB activating IKK complex including: (1) elucidating mechanism(s) of action of IKKa and how they differ from IKKb, (2) defining the novel roles of IKKa and its differentially spliced forms to induce NF-kB transcriptional competence, (3) defining how NF-kB activation reprograms cellular gene expression on a genomic scale, (4) identifying and validating novel IKK/NF-kB target genes.
Immunoglobulin heavy chain (Igh) class switch-recombination (CSR) exchanges m heavy chain constant regions (CH) of primary response IgM antibodies for g, e or a constant regions of secondary response IgG, IgE and IgA antibodies respectively. CSR is differentially controlled by specific cytokines and is also co-dependent on site specific transcription and RNA splicing. CSR occurs between tandemly repetitious S (switch) region DNA sequences positioned 5' of each CH gene segment. CSR generally occurs as a function of B lymphocyte maturation in the germinal centers of peripheral lymphoid organs and can be temporally associated with somatic hypermutation (SHM) of functionally rearranged immunoglobulin variable region genes. We have developed retroviral substrates harboring Igh S sequences, whose parental and rearrranged derivatives can be genetically selected in culture and quantitatively assayed by PCR based detection strategies. AID (activated induced deaminase), a novel mature B cell specific cytidine deaminase, has been shown to be essential for CSR and SHM and appears to function like a DNA mutagen, which invokes the DNA double strand break repair pathway. AID may also play a role in the genesis of chromosomal rearrangements in lymphoid malignancies. We are elucidating the mechanisms of action, targeting and regulation of AID in CSR and SHM.
Selected recent publications:
Ballantyne, J., Henry, D.L., Briere, F., Mueller, J., Kehry, M., Snapper, C. and Marcu, K.B. (1998) Efficient recombination of a switch substrate retrovector in CD40 activated B lymphocytes: Implications for the regulation of the IgCH switch-recombinase. J. Immunol. 161, 1336-1347.
Geleziunas, R. Lin, X., Ferrell, E., Cunningham, T., Connelly, M.A., Marcu, K.B. and Greene, W.C. (1998) HTLV-1 Tax activation of NF-kB is mediated through the TNF- a inducible NIK and IKKa /CHUK cellular kinases. Mol. Cell Biol. 18, 5157-5165.
McKenzie, F.R., Connelly, M.A., Balzarano, D., Müller, J.R., Geleziunas, R. and Marcu, K.B. (2000) Functional isoforms of IKKa (IkB-kinase-a) lacking leucine zipper and helix-loop-helix domains reveal that IKKa and IKKb have different activation requirements. Mol. Cell. Biol. 20: 2635-2649.
Li, J., Peet, G.W., Balzarano, D., Li, X., Massa, P., Barton, R. and Marcu, K.B. (2001) Novel NEMO/IKKg and NF-kB target genes at the pre-B to immature B cell transition. J. Biol. Chem. 276: 18579-18590.
Li, X., Massa, P., Hanidu, A., Peet, G.W., Aro, P., Savitt, A., Mische, S. Li, J. and Marcu, K.B. (2002) IKKa, IKKb and NEMO/IKKg are each required for the NF-kB mediated inflammatory response program. J. Biol. Chem. 277: 45129-45140.
Greeve, J., Philipsen, A., Krause, K., Klapper, W., Heidorn, K., Castle, B.E., Janda, J., Marcu, K.B. and Parwaresch,, R. (2003) Expression of activation-induced cytidine deaminase in human B cell non-Hodgkin`s-lymphomas. Blood (in press)