Research Overview of the Brady Lab
Transition metals are tightly regulated metabolites that function as structural or catalytic cofactors for specific proteins critical to normal physiology and development. Copper (Cu) is an essential transition metal for a diverse array of biological processes. Aberrant Cu excretion and absorption are manifested in the extremely rare genetic diseases Menkes and Wilson, respectively. The study of these diseases helped elucidate the cellular machinery responsible for the proper acquisition, distribution, and utilization of Cu. Recently Cu has been found to modulate signaling cascades and gene expression signatures in the context of normal physiology as well as the pathophysiology of diseases such as cancer. However, the molecular mechanisms by which Cu directly cooperates with specific signaling molecules to govern diverse cellular functions remain largely undefined. As such, there is a great need for a better understanding of precisely how Cu is integrated into signaling networks during normal homeostasis and cancer.
For example, while investigating pharmacologically accessible signaling pathways downstream of oncogenic RAS, we recently demonstrated that genetic ablation of the high affinity Cu transporter CTR1 responsible for Cu uptake resulted in decreased RAF-MEK-ERK signaling through loss of the interaction between Cu and the kinases MEK1/2 (Figure1). This is the first example demonstrating Cu directly regulates the activity of a mammalian kinase, and hence has opened up a new way to explore how metals interact with signaling pathways. Capitalizing on the dependence of oncogenic mutations in the RAS effector protein BRAF for MEK1/2 activity, a multifaceted approach was used to examine this new signaling mechanism in the context of BRAF mutation-positive cancer. Specifically, we reported that decreasing the levels of CTR1, or introducing mutations in MEK1 that disrupt Cu binding, decreased BRAFV600E-driven signaling and tumorigenesis (Figure 1). Furthermore, Cu chelators used in the treatment of Wilson disease decreased the tumor growth of cells either transformed by BRAFV600E or engineered to be resistant to BRAF inhibition (Figure 1). This novel signaling paradigm provides a concrete intersection between Cu availability and MAPK signaling and led to the initiation of a phase I clinical trial (NCT02068079) to combine a Cu chelator with a BRAF inhibitor for the treatment of BRAF mutation-positive melanoma.
The molecular mechanisms by which Cu directly cooperates with specific signaling molecules to govern diverse cellular functions remain largely undefined. As such, there is a great need for a better understanding of precisely how Cu and other metals are integrated into kinase signaling networks during normal homeostasis and cancer. Moreover, these findings highlight the prospect of manipulating metal homeostasis as a novel means to target essential kinase signal transduction pathways in cancer via a novel mechanism of regulation. As such, our laboratory will pioneer this new area of research by utilizing a multidisciplinary approach, from in vivo mouse models of cancer, biochemistry, molecular biology, and pharmacologic interventions. Specifically, our laboratory will: i) elucidate the molecular mechanisms and cellular contexts that underlie Cu integration into the MAPK pathway, ii) systematically map the landscape of sensitivity and resistance to perturbations in Cu availability as a new strategy to target the MAPK pathway in cancer, and iii) apply these findings to other transition metals and signaling networks in normal homeostasis and cancer.
Elucidating the molecular mechanisms and cellular contexts that underlie Cu integration into the MAPK pathway.
The canonical RAF-MEK-ERK signaling cascade represents one of the most well-defined lines of communication within eukaryotic cells to promote cell proliferation, which is underscored by its involvement in approximately 85% of human cancers. Our discovery that Cu selectively regulates the canonical MAPK pathway at the level of the MEK1/2 kinases, in both Drosophila and mammalian cell settings suggests that there is an evolutionarily conserved pressure for this integration. Moreover, this is untouched territory, being the first example of Cu directly regulating the activity of a mammalian kinase. As such, elucidating the molecular mechanisms by which Cu regulates MEK1/2 will provide valuable insight into the precise cellular contexts for the intersection of Cu and the MAPK pathway.
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Mapping the landscape of sensitivity and resistance to perturbations in Cu availability as a new strategy to target the MAPK pathway in cancer.
Cu chelators such as tetrathiomolybdate (TTM), D-penicillamine, and trientine are used clinically to combat the toxic levels of Cu in the brain and liver of Wilson disease patients. It is clear from my recent finding that Cu is required for both MAPK pathway signaling and tumorigenesis, suggesting that the three-quarters of human cancers in which the RAF-MEK-ERK pathway itself or its upstream activators are aberrantly activated represent an additional disease setting for the use of Cu chelators, which may offer a safe, economically favorable complementary approach for targeting the MAPK pathway in cancer.
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Given the diverse phenotypes associated with alterations in Cu metabolism, it is likely that additional Cu-dependent signaling pathways remain to be identified that are associated with the pathophysiology of disease. While recent bioinformatics approaches suggest that the current list of known Cu binding proteins is incomplete by approximating that 1% of the eukaryotic genome encodes for the Cu proteome, predicting novel Cu binding proteins based on sequence is very difficult. Thus, our laboratory is interested in determining whether other protein kinases, which represent the most intensively targeted protein class for the treatment of cancer and other diseases, are regulated in a similar fashion by Cu and possibly other metals.
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