Signal Transduction in Immune Cells

Sangdun Choi

Division of Biology, 147-75, California Institute of Technology, Pasadena, CA 91125, USA

e-mail: schoi@caltech.edu

The objective of my research interests is to bring molecular biological approaches and contemporary functional genomics to bear on the study of signaling networks in mice and humans. The immediate objective is to study regulation of gene expressions and signaling pathways that will enhance gene discoveries and provide critical information for the completion of signal transduction in immune response.

My interest is in deciphering complex biological systems and networks using immune cells. For example, transcriptional analysis of the mouse primary B cell single/double ligand screen with 33 ligands was carried out. The data suggested interesting crosstalk in the signaling pathways downstream of the proliferative ligands such as anti-IgM, CD40L, LPS, IL-4 and CpG. B cells derived from human Bcl2 transgenic mice have sustained survival in culture. While signaling parameters measured in Bcl2 transgenic B cells showed similar intracellular calcium flux, phosphorylation of a panel of signaling proteins and chemotaxis, expression changes in glycolysis genes were observed.

We have analyzed transcriptional and cytokine changes after the addition of single or double ligands in the macrophage cell line RAW264.7. A time series examining the combinational effects of LPS/IFNγ, LPS/2MA, LPS/PGE2, LPS/ISO, LPS/C5a, LPS/CpG, LPS/PAM2, LPS/PAM3, LPS/polyIC and LPS/Taxol enabled identification of the signal networks causing non-additive effects related with Toll-like receptors and G protein coupled receptors. In addition, we found that caspase 6 is involved in enhanced T cell proliferation lacking the p85β subunit of phosphoinositide 3-kinase.

We have examined the effects on macrophage RAW and J774 cells transfected with lentiviral shRNA, siRNA or antisense oligonucleotide to develop RNA interference as a gene knockdown tool. Silencing the expression of multiple Gb subunits (Gβ1/2) in macrophage using RNA silencing machinery eliminates signaling mediated by all four families of G-proteins (Gs, Gi, Gq and G12). All GPCR-mediated cellular responses induced by PGE2, ISO, C5a or UTP were modulated but not by LPS.

In current biology, biological processes of interest are studied as complex systems of functionally interacting macromolecules. Systems biological approaches along with typical biochemical/molecular biological tools are ideal for identification of the genes and to describe the signaling pathways so that complex biological phenomena can be understood coordinately. Network perturbation as well as parallel acquisition of diverse parameters relevant for genomics will increase our understanding of how cell functions are influenced to cause illnesses such as cancers or maintain health and will guide the search for ways to repair the altered functions.