“Studies of the cell-biology and structural-biology of PACS1/SHMS Syndrome”
Date awarded: November 2018
Summary: Continuation of Cell-biology and Structural biology Research Studies from below on PACS1/SHMS Mutation
Date awarded: November 2017
Summary: We discovered PACS-1 in 1998 and we have shown that this multi-functional protein has key roles in both the cytoplasm and the nucleus. In the cytoplasm, PACS-1 mediates the trafficking of proteases, ion channels and cell surface receptors, and modulates the sensitivity of cells to induction of apoptosis. PACS-1 also shuttles to the nucleus where it interacts with chromatin modifying enzymes that modulate gene expression. We are investigating how the PACS-1 R203W disease mutation, which underlies PACS-1 Syndrome, affects the cellular function and atomic structure of PACS-1. The R203W mutation resides in the critical cargo(furin)-binding region (FBR).
We will therefore rigorously test to what extent the R203W mutation alters binding of a broad panel of important client proteins and to what extent this mutation disturbs the function of the nearby autoregulatory domain, which controls access of client proteins to the FBR. We will leverage cell-based assays that monitor PACS-1-dependent membrane traffic, apoptosis or genome stability to determine which of these pathways may be most profoundly affected by the R203W mutation. Our cell and molecular studies will be complemented by protein structure studies conducted by Dr. Angela Gronenborn’s team (University of Pittsburgh), who is using nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography to ascertain the atomic structure of PACS-1 R203W. Together, our combined studies will ground our future efforts to identify small molecule compounds that may lead to therapies for treating PACS-1 Syndrome.
“Functional Studies on PACS1/SHMS Syndrome”
Date awarded: October 2017
Summary: Our current project is grounded on our original discovery of Schuurs-Hoeijmakers syndrome (SHMS) in 2012, where we showed that ectopic expression of human PACS1 message RNA (mRNA) bearing the recurrent R203W variant was able to induce craniofacial and neurodevelopmental defects in zebrafish. Subsequently, over 50 more SHMS were identified and, strikingly, nearly all of them harbored the identical mutation, always de novo (a.k.a. not carried by either parent). The broad goals of our current project are to a) model PACS1 dysfunction in a more sophisticated series of zebrafish models that harness the true power of this model organism to both understand the molecular basis of SHMS and to build a platform suitable for drug discovery; b) to probe what is unique about the R203W position in the PACS1 protein as a means of, once again, understanding the mechanism of disease; and c) integrate these findings with parallel efforts in other laboratories to understand the biophysical properties of the protein and to engineer as mouse mutant.
As part of this work, we will study the R023W mutation in a variety of transgenic reporters that will allow us to monitor the effect of this change on different aspects of the development of the central nervous system and the craniofacial skeleton. We will also ask whether it is the loss of the arginine at position 203 or the gain of the tryptophan that is the true driver of disease through a series of mutagenesis experiments around this residue. Finally, we will investigate whether the 203W mutation exerts the same effect in the context of the mouse PACS1 sequence as a pre-amble of engineering the mouse mutant by our colleagues. At the completion of this work, we will have gained a better understanding of the effect of this mutation; we will have identified subsets of cell types that might be contributing to the pathology (and can therefore be purified and studied in greater depth); and we will have formed the foundation for developing a rational drug discovery paradigm.