Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - CrIC (Molecular basis of the cross-talk between chronic inflammation and cancer)

Teaser

Chronic inflammation is a well-established hallmark of cancer. Within this proposal, I aim at investigating the molecular basis underlying cancer related inflammation (CRI). My primary working model in the Fanconi Anemia (FA) cancer susceptibility syndrome. This autosomal...

Summary

Chronic inflammation is a well-established hallmark of cancer. Within this proposal, I aim at investigating the molecular basis underlying cancer related inflammation (CRI). My primary working model in the Fanconi Anemia (FA) cancer susceptibility syndrome. This autosomal recessive disease is characterized, besides heightened cancer susceptibility, by severe defects of the immune system, increased pro-inflammatory cytokine levels and progressive bone marrow failure. My previous work has established that the SLX4 protein involved in the FA DNA repair pathway, is directly involved in the control of spontaneous pro-inflammatory cytokine production, a property mediated by its ability to form a nucleic acid processing complex.
We have now established absence of FA proteins leads to accumulation of cytosolic nucleic acids that can be recognized by the innate immune system leading to pro-inflammatory cytokine production. Accumulating cytosolic nucleic acids comprise sequences deriving from active endogenous retroelements. Furthermore, absence of FA proteins leads to upregulated endogenous retroelement activity. In addition, treatment of FA cells, or of cells exposed to replication stress inducing drugs, with a reverse transcriptase inhibitor, decreases pro-inflammatory signals. Altogether our data show that endogenous reverse transcriptase activities are involved in sustaining chronic inflammation.
We also show that the cytosol of FA patients-derived cells contain additional nucleic acid species, including DNA:RNA hybrids. The goals of ongoing investigations are (1) to identify these nucleic acids, (2) to determine how they are generated and (3) recognized by the innate immune. The consequences of cytosolic nucleic acid accumulation on cancer progression and resistance to treatment will be assessed together with the impact on the onset of pancytopenia in FA. Thus, the present project should unveil the relationship between repression of pro-inflammatory cytokine production by proteins involved in DNA repair, DNA damage, and CRI. Altogether, our work should open unforeseen perspectives in the treatment of cancer patients by allowing prevention of the pervasive effects of inflammation on tumorigenesis.

Work performed

We have now established that cell derived from FA patients present accumulation of cytosolic nucleic acids. Our initial goal was to determine the nature of the latter. We show that ssDAN, dsDNA and DNA:RNA hybrids are present in the cytosol of tested FA cells. We further show that cytosolic DNA present in FA cells are sensed by the STING-cGAS pathway to trigger the production of type I IFN. Importantly, we show that such cytosolic nucleic acids comprise sequences deriving from active endogenous retroelements, in particular from active Long interspersed elements (LINE-1). This finding is of particular importance because we show that treating FA-patients derived cells with reverse-transcriptase (RT) inhibitors, at doses that can prevent endogenous retroelement retrotransposition, decreases the production of pro-inflammatory cytokines. Furthermore, we show that treating chemotherapy-challenged cells with RT inhibitors also leads to a marked decrease of pro-inflammatory mediators. These findings have been published in EBioMedicine (DOI : 10.1016/j.ebiom.2016.05.005) and presented in international meetings.

Final results

A role for endogenous retroelements in several inflammatory disorders has been reported in the past. Our work demonstrates that absence of FA proteins leads to upregulated LINE-1 activity together with increased LINE-1 DNA accumulation in the cytosol. While a mutagenic role for LINE-1 in tumorigenesis has been reported in the past, our work presents a novel route through which LINE-1 elements contribute to foster cancer. Indeed, our recently published work establishes a role of upregulated endogenous retroelement activity in sustaining inflammation in FA. Inflammation plays a key role in the progression of FA, but the underlying molecular mechanisms remained poorly understood. The fact that treatment with RT inhibitors decreases inflammation in FA cells, raises the possibility that treating FA patients with RT inhibitors may decrease chronic inflammation and therefore potentially delay the pancytopenia that results from chronic stimulation of the immune system. In addition, our observations also provide one with a novel tool to try and decipher whether inflammation precedes DNA damage – or the converse – in FA.
Our data also provide novel investigation avenues for decreasing the side effects of chemotherapy. Indeed, we show that combining RT inhibitors with chemotherapy decreases pro-inflammatory cytokine production. This is of particular importance because of the role played by chronic inflammation in the emergence of clones displaying resistance to treatment.
Thus, our work has implications beyond the FA pathology and we are currently investigating the implications of our findings for additional cancers.