The Blind Lab

​

The role of small signaling molecules in directly regulating gene expression is far from completely understood. Perhaps the most intriguing are the phosphoinositide lipids (PIPs), which exist in nuclear compartments independent of any known membrane structure. Up to 40% of nuclear PI(4,5)P2 (PIP2) and 80% of PI(3,4,5)P3 (PIP3) are observed in this non-membrane state in every yeast, plants and metazoan cell examined to date. These non-membrane PIPs are likely bound to nuclear proteins; however their form and function have been grossly understudied, largely due to the lack of any model system.

 

The only nuclear proteins that definitively bind nuclear PIP2 and PIP3 are the highly homologous NR5A nuclear receptors (NR5A1, Steroidogenic Factor-1 and NR5A2, Liver Receptor Homolog-1). NR5As function biologically as ligand-activated transcription factors, and are widely expressed in all metazoans but not lower eukaryotes. Work from our lab demonstrated that PIP2 represses NR5A1, while PIP3 activates NR5A1 function in gene expression.

 

Our lab’s crystal structures of NR5As bound to PIPs show the acyl tails buried in the receptor core, but the inositol head group solvent exposed. Our lab showed that one lipid kinase (inositol polyphosphate multikinase, IPMK) can directly modify PIP2 while it is bound to NR5A1, activating NR5A1 function in gene expression 3 . NR5A1 remains the only well-characterized nuclear PIP3 receptor and despite the importance of PIP2 & PIP3 in many cell processes it remains unknown if IPMK regulates any other nucleoprotein/PIP2 complex.

 

My hypothesis states that nuclear PIP3 regulates many nuclear proteins, by acting as molecular glue between DNA-binding factors and transcriptional co-regulators. As a first test of this hypothesis, I will determine if IPMK regulates NR5A2 in the same way IPMK regulates NR5A1, through a set of very feasible, zero-sum experiments. Strong preliminary data I generated suggest nuclear PIP3 functions as molecular glue between NR5A1 and phospholipid binding domain-containing proteins. Thus I will test if nuclear PIP3 provides a physical link between NR5A and phospholipid binding domain-containing proteins, in the context of chromatin in human cell lines.

​

​

​