The Role of Bruton's Tyrosine Kinase in B-cell Anergy

Project Summary: Although researchers once thought that immune cells are incapable of targeting the body’s own tissues, this turns out not to be true. A population of hyporesponsive, or anergic, B cells retains autoreactive B-cell receptors. When proper maintenance of B-cell anergy is disrupted, autoimmunity results. Recently, it has become clear that Bruton’s Tyrosine Kinase (Btk) is important to maintain B-cell anergy. But the structural features of Btk responsible for controlling the balance between anergy and responsiveness are not understood. One clue to how Btk maintains anergy comes from comparing Btk with its sister kinase, Itk, expressed in T cells. These kinases are remarkably similar but have different activation mechanisms. Btk evolved the ability to dimerize on the plasma membrane, enhancing its kinase activity, but Itk did not. The unique ability of Btk to dimerize arose early in the evolution of jawed vertebrates when adaptive immunity first emerged. Dimerization endows Btk with a switch-like activation in response to changing PIP3 levels on the plasma membrane, which are known to be important for controlling anergy. In this work, I propose to investigate how Btk uses dimerization to maintain B-cell anergy. First, I will determine how dimerization helps Btk adsorb to plasma membranes (aim 1). Then, I will develop a TIRF microscopy-based approach to examine how dimerization underlies B-cell signaling (aim 2). Finally, I will determine how modulating dimerization alters the fraction and signaling of anergic B cells (aim 3). This work aims to impact human health. The 2013 approval of the small-molecule kinase inhibitor ibrutinib, which targets Btk, was a major breakthrough in cancer treatment. Now this molecule and other Btk inhibitors are in clinical trials for autoimmune disorders. But the role of Btk in autoimmune signaling is a fundamentally different problem than the well-studied role of Btk in cancer. This proposal will pave the way for more specific therapeutics that treat autoimmunity without completely disrupting B-cell function. This research will be performed in the laboratory of Dr. Jay Groves at UC Berkeley. I have assembled a mentorship team consisting of Dr. Groves, Dr. John Kuriyan (Vanderbilt University), and Dr. Julie Zikherman (UC San Francisco), each of whom contribute unique and exceptional expertise to further the goals of this proposal. As a postdoc in Dr. Kuriyan’s group, I developed saturation-mutagenesis methods to examine Btk, resulting in the discovery that Btk signaling depends on dimerization in some cellular contexts. Here, I build on that discovery to investigate dimerization using single-molecule imaging and an in vivo anergy model. The highly collaborative nature of this work, and the rich research setting of UC Berkeley, will enable me to train in the interdisciplinary areas that are essential for my future as an independent investigator in molecular immunology.