Cell growth is regulated by coordination of both extracellular nutrients and intracellular metabolite concentrations. A large number of proteins receive signals from outside and orchestrate the intracellular response using nucleotides as second messengers. Unbalanced production, malfunction or changes in the stability of individual proteins cause pathologies.
In bacteria, biofilm formation is one of the most studied processes governed by nucleotide signalling. A key player in biofilm development is the cyclic dinucleotide c-di-GMP: environment triggers the activation of specific pathways to control c-di-GMP levels and to re-shape the energetic and metabolic profile of the cell. Given the huge impact of biofilms on human health, understanding the molecular details of c-di-GMP metabolism represents a critical step for the development of novel therapeutics against bacterial biofilms.
Very recently, in eukaryotes, the involvement of cyclic dinucleotides (CDNs), including the aforementioned c-di-GMP, in the innate immunity response has been established, through the activation of the inflammosome via the CDNs receptor STING. Prolonged inflammatory stress contributes to cellular transformation, which, in turn, involves a huge metabolic re-programming to sustain cell division (including the re-shaping of the energy and the one-carbon metabolism).
Therefore, as for bacteria, also in eukaryotes, CDNs sensing is undoubtedly associated to extensive metabolic reprogramming, whose molecular details controlling are yet to be defined.
Our major goal is to understand the structure and function of proteins at the interface between CDNs sensing and metabolism. We tackle this issue by studying various processes in prokaryotic and eukaryotic cells, including biofilm formation, host-pathogen interactions and metabolic reprogramming in cancer cells, both in hypoxia and normoxia, given the importance of hypoxia in both biofilm and cancer.
The exceptional importance of CDNs in prokaryotes and eukaryotes as a common strategy to control crucial cellular fates is by now acknowledged by the scientific community; the idea that these signalling pathways cross and affect pathways of the basal metabolism is now emerging. Given the crucial role of basal metabolism in determining the final output (mostly relevant to human health, such as biofilm formation or cancer), understanding the molecular details controlling the communication between CDNs signalling and metabolism is mandatory for the development of future strategies to control cell destiny.
For bacteria, anti-biofilm strategies aimed at interfering selectively with the metabolic re-programming necessary to trigger biofilm formation via CDNs sensing, particulary c-di-GMP for Gram-negative chronic infections; however, despite the promising results in vitro, up to now the identified approaches were found to be ineffective and poorly selective on cells (9-11).
Nevertheless, the potential therapeutic impact deriving from the inhibition of biofilm via c-di-GMP in human diseases is huge: according to the NIH, 65-80% of all infections in developed countries are caused by biofilms. In 2000, the Center for Disease Control and Prevention (CDC) announced biofilms and biofilms-mediated infections as two of seven major healthcare problems facing the medical community in the 21th century. Biofilms cost Europe billions of euros each year in medical infections, equipment damage, energy losses and product contamination. Related issues include deterioration of dental surfaces, contamination of surfaces in the food processing industry, and the deterioration of air quality in ventilation and air handling systems. Bacterial biofilms on the surface of indwelling medical devices (such catheters) or on chronic wounds are a major cause of hospital-associated infections, with high morbidity and mortality, placing a $35 billion burden in the US healthcare system annually (estimate 2009) (12).
The knowledge of c-di-GMP metabolism may offer the intriguing possibility to control bacterial motility at will, by interfering with such CDNs signalling system; in parallel, the identification of specific CDNs-dependent pathway(s) relevant to control basal metabolism will be helpful to improve the selectivity of targeting c-di-GMP-metabolism.
Besides those outlined above, other relevant biomedical and biotechnological applications of this project can be foreseen, moving to eukaryotes. Indeed, c-di-GMP is also a vaccine adjuvant (13) and eukaryotic intracellular receptors have been identified able to elicit the immune response in the host (14); novel c-di-GMP analogues found in this project might also find potential applications in immunotheraphy. Intervention on innate immunity may thus offer the possibility to develop novel chemical tools to modulate cancer metabolism and open new translational opportunities for drug development and biomarker identification. The long-term goal is to provide targeted anti-metabolic therapy, hopefully more selective than traditional chemotherapy, still widely employed in cancer treatment, to be combined to modulation of innate immunity.
The outcomes of our project will allow gaining an insightful picture of the role of CDNs sensing in controlling all the metabolic pathways relevant to the metabolic shift (including the Warburg effect) relevant to tumorigenesis. Indeed, although a link between i) inflammation and cancer; ii) unbalanced CDNs and chronic inflammation; iii) metabolic re-programmic and cancer has been acknowledged by the literature, the crosstalk between the inflammation world (i.e. CDNs sensing) and metabolism is still elusive. It is clear that unveilling the details on such missing link is mandatory to understand cancer progression and to find a targeted strategy to block such progression.
The main goals of this project are achievable, also considering the unique and complementary expertise of the RU members and the features and reputation of the Department of Biochemical Sciences, where the project will be carried out (see the next paragraph for details).