Associate Professor of Cell Biology
Seeley G Mudd 520
250 Longwood Avenue
Boston, MA 02115
Lab Size: Greater than 5
Our lab has two main interests: 1) Understanding the mechanisms involved in cell-cell signaling through the vertebrate Hedgehog pathway; and 2) Synthesizing and validating new chemical probes for microscopic imaging and functional assays of various biological molecules (nucleic acids, proteins, lipids), in cells and in animals.
1) Mechanisms of Hedgehog signaling
The Hedgehog pathway plays a critical role in developing embryos as well as in the maintenance of adult stem cells. Unregulated Hedgehog signaling is implicated in a large number of human cancers. We are using biochemistry, cell and chemical biology to elucidate how vertebrate cells send and respond to Hedgehog signals. The key questions of Hedgehog signaling that we are investigating are:
- How is the secreted Hedgehog protein activated?
Hedgehog becomes active through a unique posttranslational process involving the attachment of both cholesterol and palmitate. We are using biochemistry to reconstitute these complex reactions and dissect their mechanism. We also use live cell imaging to investigate the subcellular dynamics of Hedgehog activation. Finally, we are using chemical biology approaches to identify other cholesterol-modified proteins and study them functionally in cells.
- How does Hedgehog signaling control the Gli transcription factors?
In vertebrates, Hedgehog signaling initiated in primary cilia activates the membrane protein Smoothened and leads to activation of Gli proteins, the transcriptional effectors of the pathway. In the absence of signaling, Gli proteins are inhibited by the cytoplasmic protein SuFu. We found that Hedgehog stimulation quickly recruits endogenous SuFu-Gli complexes to cilia and causes rapid dissociation of the SuFu-Gli complex, thus allowing Gli to enter the nucleus and activate transcription. We are using biochemical reconstitution and cell biology to dissect this simple mechanism of vertebrate Hedgehog signaling. We plan to use live cell imaging to understand the spatial and temporal aspects of SuFu-Gli regulation by Hedgehog signaling at the primary cilium.
- What is the role of sterols in Hedgehog signal transduction?
Sterols are required for normal Hedgehog signaling and Hedgehog signaling is defective human diseases of cholesterol metabolism. Furthermore, oxysterols are potent activators of the Hedgehog pathway, suggesting a role for endogenous sterols in Hedgehog signaling. We are using chemical biology, biochemistry and cellular approaches to understand how sterols regulate the membrane protein Smoothened, which is critical for transducing Hedgehog signals.
2) Novel chemical probes for imaging and studying biological molecules
Our lab is developing and using new chemical probes for metabolically labeling biological molecules, followed by their detection through bio-orthogonal chemical reactions. Past work focused on high-resolution microscopy probes for DNA, RNA and choline phospholipids. We are currently developing, characterizing and using probes for nascent proteins, sterols, and other classes of phospholipids.
1) Nedelcu D, Liu J, Xu Y, Jao C and Salic A – 2013 Oxysterol binding to the extracellular domain of Smoothened is required for vertebrate Hedgehog signaling, Nat Chem Biol, advance online publication.
2) Tukachinsky H, Kuzmickas RP, Jao CY, Liu J and Salic A – 2012 Dispatched and Scube mediate the efficient secretion of the cholesterol-modified Hedgehog ligand, Cell Rep, 2(2), 308-20.
3) Liu J, Xu Y, Stoleru D, and Salic A – 2012 Imaging protein synthesis in cells and tissues with an alkyne analog of puromycin, PNAS, 109(2), 413-8.
4) Chen X, Tukachinsky H, Huang CH, Jao C, Chu YR, Tang HY, Mueller B, Schulman S, Rapoport TA and Salic A – 2011 Processing and turnover of the Hedgehog protein in the endoplasmic reticulum, J Cell Biol, 192(5), 825-38.
5) Tukachinsky H, Lopez L and Salic A – 2010 A mechanism for vertebrate Hedgehog signaling: recruitment to cilia and dissociation of SuFu-Gli protein complexes, J Cell Biol, 191(2), 415-28.