Microbial mobilization of the actin cytoskeleton

PROJECT SUMMARY/ABSTRACT The actin cytoskeleton is crucial for cellular properties and behaviors including shape, migration, and division. It is also critical for cell-cell and cell-extracellular matrix connections as well as cell-cell fusion. Because of these numerous essential functions in cell physiology, actin dysfunction is also a common contributor to pathogenesis, for example, in inflammation, cardiovascular disease, cancer metastasis, and microbial infection. Despite many years of study, however, understanding how actin assembly is regulated and harnessed in the cytoplasm and nucleus for intracellular events, cellular behaviors, and cell-cell interactions remains a key outstanding problem in cell biology. In our NIGMS-funded research, my lab has taken a distinctive approach to address this important gap in knowledge, which is to examine the interactions between microbes that do not cause serious human illness and the host cell actin cytoskeleton as a window into actin regulation and function. Our approach leverages the fact that microbes colonize host cells through their ability to target actin, often eliciting amplified cellular responses by mimicking or manipulating host molecules, making them powerful tools for revealing molecular mechanisms of actin regulation and function. This scientific premise is supported by many examples of how studying microbe-host interactions has enhanced our understanding of basic cell biological processes. The research described in this MIRA application makes use of microbes as tools to address three fundamental cell biological questions: (1) How is actin polymerization at membranes regulated and mobilized to drive movement? (2) How and why is actin transported into and polymerized within the nucleus for gene expression, nuclear organization, intranuclear movement, and nuclear envelope dynamics? (3) How is actin polymerization in plasma membrane protrusions harnessed to induce cell-cell fusion? We will investigate these questions using three model microbes that infect cells and mobilize actin in a manner that makes them powerful cell biological tools: Mycobacterium marinum as a tool to understand the regulation of actin assembly at membranes to drive intracellular movement; the baculovirus Autographa californica multiple nucleopolyhedrovirus as a tool to understand the regulation and function of actin in the nucleus; and Burkholderia thailandensis as a tool to understand the role of actin in cell-cell fusion. By leveraging our expertise in both cell biology and microbiology, and deploying a synergistic combination of microbial and host genetic methods, advanced imaging approaches, and biochemical methods, we are uniquely positioned to advance the field. Our results will enhance our understanding of the mechanisms of actin regulation and may provide new insights into diagnosing, treating, and preventing diseases associated with actin dysfunction.