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Michael E. Hurwitz PhD, MD

Assistant Professor of Medicine (Medical Oncology)

Research Interests

Cell migration; Kinase signaling; Phosphorylation; Cytoskeleton; Engulfment; Apoptosis; C. elegans; Cancer biology


Research Summary

Abl Kinase Regulation of the Cytoskeleton

Cytoskeletal changes are vital both for normal processes such as physiologic cell migration, engulfment (e.g. phagocytosis) and tissue morphogenesis and for pathologic ones such as cancer cell invasion and metastasis. We study the regulation of cell migration and apoptotic cell engulfment in the roundworm C. elegans to understand cytoskeletal regulation. Because the cell lineage of the worm is invariant, every cell migration and engulfment event throughout the organism's life is known, which allows us to analyze at a single-cell level how specific molecular changes affect these processes. We identified ABL-1, the homolog of the Abl tyrosine kinase, as an inhibitor of cell migration and apoptotic cell engulfment. We further showed that ABL-1 does so through the cytoskeletal regulator ABI-1, a protein not previously shown to regulate these processes.

Extensive Research Description

Abl Kinase Regulation of the Cytoskeleton

Cytoskeletal changes are vital both for normal processes such as physiologic cell migration, engulfment (e.g. phagocytosis) and tissue morphogenesis and for pathologic ones such as cancer cell invasion and metastasis. We study the regulation of cell migration and apoptotic cell engulfment in the roundworm C. elegans to understand cytoskeletal regulation. Because the cell lineage of the worm is invariant, every cell migration and engulfment event throughout the organism's life is known, which allows us to analyze at a single-cell level how specific molecular changes affect these processes. We identified ABL-1, the homolog of the Abl tyrosine kinase, as an inhibitor of cell migration and apoptotic cell engulfment. We further showed that ABL-1 does so through the cytoskeletal regulator ABI-1, a protein not previously shown to regulate these processes.

In addition to its role in cytoskeletal regulation, Abl functions in apoptosis, transcription and the responses to oxidative stress. Dysregulation of Abl via fusion to the BCR gene causes Chronic Myelogenous Leukemia (CML) and an aggressive subtype of Acute Lymphoblastic Leukemia (ALL). Emerging data implicate Abl signaling in several solid tumors also but how Abl signaling is involved is unknown. Our laboratory aims to characterize the role of Abl signaling in normal cell function and disease.

Using genetic, cell biological and proteomic approaches we are asking a number of related questions: How is ABL-1 regulated? What are the ABL-1 phosphorylation targets and which ones regulate engulfment and migration? What are other inhibitors of engulfment pathways? In what other processes does ABL-1 function? Are these roles conserved across species? How are the various functions of ABL-1 integrated to accomplish specific goals during an organism’s development?

Project 1. Assess the functions of C. elegans homologs of mammalian Abl and Abi interactorsWe are using a candidate approach to identify proteins that act in ABL-1-dependent pathways based on reports of Abl and Abi-interacting proteins from the scientific literature in mammals. The vast majority of the over 100 proteins reported to interact with Abl and Abi have homologs in C. elegans. While functions have been ascribed to some of these interactions, the significance of many of them is unclear. We have already demonstrated that some of these homologs have effects on apoptotic cell engulfment and are now analyzing how they function in this process.

Project 2: Phosphoproteomic Analysis of abl-1 mutantsUsing mass spectroscopy, the laboratory of Matthias Mann has recently published a technique to determine the in vivo C. elegans phosphoproteome, i.e. the entire set of phosphorylated peptides in adult C. elegans. Because abl-1 is expressed broadly throughout embryogenesis, my laboratory, in collaboration with Dr. Mann’s group, will determine the phosphoproteomes of wild-type and abl-1 C. elegans embryos. This will be the first analysis of the effect of deletion of a tyrosine kinase on the phosphoproteome of an entire organism. Notably, this technique will not only assess the effect on tyrosine phosphorylation, but also on the phosphorylation of serines and threonines so secondary effects of Abl function on other signaling pathways will also be evaluated by this technique. We will analyze the differentially phosphorylated proteins for their roles in the processes in which ABL-1 functions.

Project 3. Identify and characterize essential roles for ABL-1It is likely that ABL-1 has functions in C. elegans in processes other than those described above. Loss of abl-1 is not lethal to C. elegans, probably because there are other proteins that act in parallel to ABL-1 for many of its roles. To identify such proteins and the processes in which they act, we screened a C. elegans RNAi library for synthetic lethality with abl-1. RNAi clones that specifically killed abl-1mutant animals but not wild-type animals might have reduced the activity of proteins required for viability in the absence of ABL-1 function. Thus, this screen should have identified genes that act in parallel to abl-1 in pathways vital for the animal’s survival. 108 such genes were identified, most of which are conserved in mammals. Among the 108 genes are many that appear promising for future study, including genes or homologs of genes involved in cytoskeletal regulation, cell migration, cellular signaling and transcription. In addition there are genes that are conserved but without known functions. Such genes are particularly promising candidates for finding novel biological roles for ABL-1. All of these will be analyzed for Abl-related functions.

Project 4. Use a mammalian cell culture assay to test conservation of C. elegans ABL-1 findingsTo test whether Abl functions in mammalian engulfment, we are using a cell culture-based mammalian engulfment assay. Because all known C. elegans engulfment genes and abl-1 are conserved in mammals, RNAi against or overexpression of each of the mammalian homologs of engulfment genes and abl-1 can be used to test the effects on engulfment. In addition, we will test any new conserved genes identified by the other screens.

Project 5. Expression analysis of abl-1 mutantsIn combination with the phosphoproteomic analysis, an expression analysis will be performed to compare abl-1 mutants to wild-type animals using RNA-seq, a method to quantitate expression levels of all transcripts in the animal by deep sequencing of cDNAs transcribed from the animals’ RNA. By comparing the two expression patterns, we hope to gain a global view of the effect of ABL-1 on the transcriptome. Combining these data with the phosphoproteomic analysis, a comprehensive overview of the effect of ABL-1 on two major and often interrelated processes, phosphorylation and transcription, can be constructed.

Our lab aims to analyze globally what ABL-1, the homolog of an important disease-related kinase, does in an organism in vivo. This type of approach might allow us to begin to understand how the various functions of a kinase are integrated within an organism to accomplish general developmental goals. Furthermore, these experiments should provide useful information about processes in which ABL-1 is known to act and could lead to the discovery of new functions for ABL-1. In addition, because there are a large number of well-defined tissue-specific and temporally regulated promoters in C. elegans, later studies can be used to define where and when certain ABL-1 interactors act, which could lead to better understanding of signaling networks.


Selected Publications

  • Hurwitz M.E., Vanderzalm P.J., Bloom L., Goldman J., Garriga G., and Horvitz, H.R. (2009) Abl kinase inhibits the engulfment of apoptotic cells in C. elegans. PLoS Biol 7(4): e1000099.
  • Vanderzalm, P.J., Pandey, A., Hurwitz, M.E., Bloom, L.., Horvitz, H.R., and Garriga, G. C. elegans CARMIL negatively regulates UNC-73/Trio function during neuronal development. Development. 2009;136: 1201-1210.

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