Research

Autophagy and Infection
Autophagy and Cancer Biology
Autophagy and Cell Death Regulation

 

Autophagy and Infection

Our laboratory has defined an evolutionarily conserved role for autophagy genes in innate immunity against viruses and bacterial infections. Present studies are aimed at understanding: (1) how intracellular pathogens are recognized by the autophagic machinery; (2) how autophagy limits viral replication and intracellular bacterial multiplication; (3) how autophagy regulates cell death and cell survival in infected cells and tissues; (4) whether declines in autophagy function with aging contribute to age-related increases in susceptibility to infectious diseases; (5) which strategies intracellular pathogens use to evade host autophagy; and (5) the role of viral evasion of autophagy in viral pathogenesis, including acute infection and chronic medical diseases (e.g. cancer and neurodegenerative diseases). To accomplish these goals, we are currently studying two viruses that infect the central nervous system and cause lethal encephalitis, Sindbis virus, and herpes simplex virus; a murine gammaherpesvirus that provides a model for human oncogenic gammaherpesviruses; and the intracellular bacteria, Salmonella typhimurium, an important cause of enteric infection. We are employing a variety of cell biology, biochemistry, and genetic approaches in tissue culture and animal model systems to understand the role of autophagy in combating these pathogens, and the role of autophagy evasion in microbial pathogenesis. The principles that we uncover in our studies of these organisms are likely to have broad relevance to a variety of different intracellular pathogens and result in new ways of thinking about host-pathogen interactions and the pathogenesis of infectious diseases.  
A falsely colored electron micrograph of a herpes simplex virus-infected mouse neuron showing an autophagosome that is degrading herpes simplex virions (viral constituents are colored pink)

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Autophagy and Cancer Biology

Our laboratory has shown that Beclin 1, an autophagy execution protein, is a haploinsufficient tumor suppressor protein. Monoallelic deletions of beclin 1 are found in the majority of cases of sporadic human breast and ovarian carcinoma, and heterozygous deletion of beclin 1 in mice results in mammary neoplastic lesions, lung adenocarcinomas, hepatocellular carcinomas, and B cell lymphomas. Present studies relating to autophagy and cancer are aimed at: (1) investigating whether the tumor suppressor effects of Beclin 1 are mediated through autophagy; (2) identifying the precise mechanisms by which autophagy functions in negative growth control and tumor suppression; (3) evaluating the role of mutations of other autophagy execution genes in cancer, using gene knockout approaches in mice and mutational analyses of human cancers; (4) investigating the role of autophagy inhibition in oncogenesis mediated by Bcl-2 family members and the Class I/PI3K/Akt signaling pathway; and (5) screening small molecule libraries to identify novel compounds that increase Beclin 1 expression and restore autophagy in tumor cells.  
A ductal carcinoma in situ lesion in the mammary gland of a 9 month-old female beclin 1 heterozygote-deficient mouse

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Autophagy and Cell Death Regulation

Autophagy is frequently observed in dying cells. However, it has been unclear whether autophagy is a form of non-apoptotic programmed cell death, whether it is activated as part of a cellular survival strategy, or whether it is activated to clean up the remnants of dying cells. With the identification of the evolutionarily conserved molecular machinery, it has become possible to use genetic approaches to resolve this controversy. The preponderance of genetic evidence to date indicates that autophagy is primarily a pro-survival mechanism, but in certain contexts, can also be a mechanism of cell death. We have found that the interaction between the anti-apoptotic protein, Bcl-2, and the autophagy protein, Beclin 1, functions as a rheostat that controls levels of cellular autophagy and autophagic cell death. Current studies are aimed at: (1) identifying the mechanisms by which Bcl-2 inhibits the autophagy function of Beclin 1; (2) identifying the upstream signaling events that regulate Bcl-2-Beclin 1 binding; (3) evaluating the role of Bcl-2 inhibition of autophagy in oncogenesis; (4) evaluating the role of Bcl-2 and Beclin 1 binding in cell death regulation during embryonic development; (5) evaluating the role of the interaction of the C. elegans orthologs of Bcl-2 and Beclin 1, CED-9 and BEC-1, in programmed cell death and development; (6) performing crystallographic analyses of the Bcl-2/Beclin 1 and CED-9/BEC-1 complexes; and (7) evaluating the role of autophagy in the clearance of dead cells during embryonic development.

Physiological levels of autophagy (shaded region of center graph) are essential for normal cellular homeostasis, and the absence of autophagy genes (shaded region of left graph) increases cell death during nutrient deprivation and other forms of cellular stress. In contrast, excessive, non-physiological levels of autophagy (shaded region of right graph) promote autophagy gene-dependent cell death. The relative amounts of Beclin 1 and Bcl-2 (or perhaps other Bcl-2 family members) complexed with each other within a cell govern the threshold for transition from cell homeostasis (center graph) to cell death (right graph).