Wnt pathways
One of our research interests is to delineate the Wnt signaling pathways that control early development. Three Wnt signaling pathways conserved from fly to human are known: Wnt/b-catenin (canonical), Wnt/cGMP/Ca2+ (non-canonical), and planar cell polarity (Wnt PCP) pathway. Disruption of Wnt pathways blocks development and induces early death. Abnormal activation of Wnt/b-catenin pathway, in particular, induces cancer. We established that Wnt signaling pathways are G-protein-coupled signaling pathways. Recently, my laboratory has demonstrated that inositol pentakisphoaphate, IP5, mediates Wnt3a-stimulated canonical signaling, operating at the level above GSK3b. Inositol phosphate 3 kinase (IP3K) and inositol phosphate multikinase (IPMK) are key enzymes to generate IP5 in cells. One of our research focuses is to understand the regulation and function of IPMK in Wnt canonical signaling.
The phosphoprotein scaffold Dishevelled is an essential component of both Wnt signaling and of the signalsome that constitutes the supermolecular “punctae” of assembled proteins often observed in fluorescence microscopy. Although replete with proteins that are known to dock to the three well-known domains (i.e., DIX, PDZ, and DEP) of the fly Dishevelled (Dsh) and the vertebrate isoforms of Dishevelled (i.e., Dvl1, Dvl2, and Dvl3), the C-terminal region beyond the DEP domain displays unique and interesting character. We are using biophysical, biochemical and cell biological methods to delineate the structural and functional importance of the C-terminal region of Dvl in Wnt signaling.
The role of Wnt/Frizzled pathways in differentiation and self-renewal of Human embryonic stem cells
Human embryonic stem cells (hESC) provide both a great model for analysis of cell signaling and development. Human ESC are totipotent and their therapeutic potential is highest if they can be provoked to defined stem cell populations that are homogenous and predictable in their growth and end-point differentiation (e.g., cardiac muscles cells, pancreatic beta cells, neural cell types). The inherent heterogeneity of hESC must be overcome if well-defined end-point populations are to be created, interrogated for their individual cell-type specific gene expression, and employed in therapeutics. Wnt ligands act on Frizzleds to guide cell development. We are using a novel method by which stimulation of each Frizzled can be achieved without a Wnt (which can activate more than one Frizzled type). We will characterize programmed cell differentiation and/or self-renewal of hESCs.
