Metabolic inhibitors accentuate the anti-tumoral effect of HDAC5 inhibition

The US FDA approval of broad-spectrum histone deacetylase (HDAC) inhibitors has firmly laid the cancer community to explore HDAC inhibition as a therapeutic approach for cancer treatment. Hitting one HDAC member could yield clinical benefit but this required a complete understanding of the functions of the different HDAC members. Here we explored the consequences of specific HDAC5 inhibition in cancer cells. We demonstrated that HDAC5 inhibition induces an iron-dependent reactive oxygen species (ROS) production, ultimately leading to apoptotic cell death as well as mechanisms of mitochondria quality control (mitophagy and mitobiogenesis). Interestingly, adaptation of HDAC5-depleted cells to oxidative stress passes through reprogramming of metabolic pathways towards glucose and glutamine. Therefore, interference with both glucose and glutamine supply in HDAC5-inhibited cancer cells significantly increases apoptotic cell death and reduces tumour growth in vivo; providing insight into a valuable clinical strategy combining the selective inhibition of HDAC5 with various inhibitors of metabolism as a new therapy to kill cancer cells.

HDAC5 is required for maintenance of pericentric heterochromatin, and controls cell-cycle progression and survival of human cancer cells

Histone deacetylases (HDACs) form a family of enzymes, which have fundamental roles in the epigenetic regulation of gene expression and contribute to the growth, differentiation, and apoptosis of cancer cells. In this study, we further investigated the biological function of HDAC5 in cancer cells. We found HDAC5 is associated with actively replicating pericentric heterochromatin during late S phase. We demonstrated that specific depletion of HDAC5 by RNA interference resulted in profound changes in the heterochromatin structure and slowed down ongoing replication forks. This defect in heterochromatin maintenance and assembly are sensed by DNA damage checkpoint pathways, which triggered cancer cells to autophagy and apoptosis, and arrested their growth both in vitro and in vivo. Finally, we also demonstrated that HDAC5 depletion led to enhanced sensitivity of DNA to DNA-damaging agents, suggesting that heterochromatin de-condensation induced by histone HDAC5 silencing may enhance the efficacy of cytotoxic agents that act by targeting DNA in vitro. Together, these results highlighted for the first time an unrecognized link between HDAC5 and the maintenance/assembly of heterochromatin structure, and demonstrated that its specific inhibition might contribute to increase the efficacy of DNA alteration-based cancer therapies in clinic.

Regulation of serotonin transporter activity by adenosine in intestinal epithelial cells

Serotonin plays a critical role in the regulation of intestinal physiology. The serotonin transporter (SERT) expressed in the intestinal epithelium determines 5-HT availability and activity. The serotoninergic system and SERT activity have been described as being altered in chronic intestinal pathologies such as inflammatory diseases. Adenosine has also been shown to be involved in a variety of intestinal functions and to play a central role in the regulation of inflammatory responses of injured tissue. Since the modulation of SERT by adenosine in the intestine remains unknown, the aim of the present work was to study the effect of adenosine on SERT activity and expression and to determine the molecular mechanism involved. The study has been carried out using human enterocyte-like Caco-2 cells which endogenously express SERT. The results show that adenosine diminishes SERT activity in both the apical and basal membranes by acting in the intrinsic molecule with no alteration of either SERT mRNA or protein levels. The effect of adenosine appears to be mediated by A(2) receptors and activation of the cAMP/PKA signalling pathway. Moreover, the adenosine effect did not seem to involve the activation of AMP activated protein kinase. Adenosine effects are reached at high concentrations, which suggests that adenosine modulation of SERT may be significant under conditions of inflammation and tissue injury.