Investigate hedgehog signaling in disease processes

The development of more efficacious therapeutics for many diseases awaits the elucidation of cellular signaling pathways that underlie the corresponding pathophysiological states. The Hedgehog pathway is important for governing normal cell growth and spatial patterning of tissues. In addition, Hedgehog signaling has also been found to sustain stem cell renewal. Thus, it is not surprising that aberrant Hedgehog pathway activity has been implicated in multiple diseases, and identifying valid molecular targets for suppressing this circuit is important for future drug development efforts. Numerous observations connect abnormalities in the Hedgehog signaling to cancer susceptibility, cancer cell growth, and metastasis. For example, Patched has been found to be a tumor suppressor; without Patched, there is a correlation with the presence of certain tumors, such as basal cell carcinoma. Also, various mutations in Smoothened that are found in some sporadic tumors have been found to confer constitutive activation of the Hedgehog pathway. Moreover, Hedgehog signaling is connected with cancer stem cell renewal. Consequently, the research performed by Dr. Salic’s laboratory into the biochemical underpinnings of the Hedgehog signaling circuit is of vital importance for contemplating strategies to therapeutically intervene and block Hedgehog’s growth promoting function. 
 

The Hedgehog signaling loop is a highly conserved pathway that operates in all animal species serving a variety of functions, in addition to its well-studied role in embryonic development. Hedgehog-mediated effects on transcription and cell-cell signaling have been linked to disease processes, providing a compelling incentive to understand at a detailed biochemical level the relationships between structure and function of the component parts of the circuit and the mechanisms of communication. Dr. Salic’s laboratory applies a diverse repertoire of methodologies to gain this understanding.  Dr. Salic is:

• Deconstructing the enzymatic steps that culminate in the unusual cholesterol modification of the C-terminus of Hedgehog. Although autocatalysis by Hedgehog can generate the cholesterol modification, the process is inefficient, suggesting that accessory factors propel the enzymatic esterification of Hedgehog with cholesterol.
   
• Searching for other cellular proteins that contain this atypical cholesterol post-translation modification.  The lab employs molecular “hooks” that can latch onto cholesterol binding sites on proteins.
   
• Investigating the signaling between the transmembrane Hedgehog receptor Patched (Patched-1 for Sonic Hedgehog) and its non-binding target, the transmembrane protein Smoothened. In the absence of Hedgehog, Patched constitutively blocks Smoothened activity, thus derailing any productive signal. The lab is attempting to unravel the mechanism by which Patched elicits suppression of Smoothened function.
   
• Studying the “terminal” events of Hedgehog signaling, when the Gli transcription factors are activated and mediate transcriptional regulation of various genes.
   
• Optimizing the EdU-based fluorescence technology for visualizing proliferating cells.
   

Dr. Salic employs molecular, cellular, and chemical approaches to the study of the Hedgehog signaling pathway, a basic biological circuit present in all multicellular organisms. The Hedgehog pathway is involved in cell-cell signaling, a fundamental process that is required for metazoan embryonic development. The Hedgehog family of protein ligands is secreted and elicits autocrine and paracine effects by binding to the cell surface receptor Patched. In addition to developmental processes, Hedgehog signaling has been implicated in a variety of malignancies, and interfering with this pathway may lead to novel cancer therapeutics. Conversely, boosting Hedgehog signaling may be a viable approach for counteracting the debilitating effects of ischemic-related episodes, such as stroke or heart attack. Dr. Salic’s laboratory has also investigated different aspects of Hedgehog signaling.

In collaboration with Timothy Mitchison, the lab investigated architectural aspects of mitosis, a tightly regulated process, including the protein networks responsible for centromere and kinetochore (that is, the site of spindle fiber attachment) functions. The attachment of microtubules to the kinetochore, spindle formation, and chromosome relocation to opposite ends of the nucleus during the mitotic process, require the coordination of numerous proteins. The lab has published studies demonstrating that the Sgo gene is important for stabilizing the kinetochore-microtuble association.

In other studies, also in collaboration with Timothy Mitchison, the lab has developed, and recently published, a novel chemical technique for monitoring cell division that has distinct advantages over currently used methodologies. When compared to radiolabel and antibody-based procedures, the use of EdU, which mimics a DNA nucleotide, can be detected by exposure to a fluorescent azide, and the fluorescence can be visualized by microscopy. The EdU method is more robust and versatile than the BrdU-antibody method, and is particularly effective at assessing proliferation within tissues where antibody access would be limited.

Biological Mechanisms and Pathways

• Cell-cell signaling •
• Cholesterol modification •
• Cholesterol-modified protein •
• Development •
• Gli •
• Hedgehog •
• Oncology •
• Patched •
• Protein-Protein interaction •
• Transcription
•  

Cancer

• Cancer •
• Oncology
•  

Disease Mechanisms

• Cancer
•  

Research Tools and Instrumentation

• Chemical detection of cell proliferation •
• Fluorescent imaging of cell proliferation •
• Live cell imaging
•  

Therapeutic Discovery Tools and Assays

• Cancer
•  

Therapeutics

• Cancer targets •
• EdU •
• Stem cell
•