P80 Inhibiting HuR/ELAVL1 activity as a novel anti-psoriatic pharmacological strategy: in vitro evidence

Abstract HuR is among the most widely studied RNA binding proteins that post-transcriptionally regulate thousands of coding and non-coding RNAs bearing AU-rich elements (AREs). It exerts both pre-mRNA processing and maturation functions and regulation of mRNA stability and translation. Interestingly, most of the chemokines and cytokines contain AREs, suggesting that HuR-dependent post-transcriptional control is crucial for the inflammatory response. HuR is ubiquitously expressed, and the outcome of its activation is context-dependent, and it is frequently deregulated in many types of cancers and immune-related diseases. Psoriasis is characterized by an intricate feed-forward interaction between the immune system and the skin through inflammatory cytokines that were identified as post-transcriptionally regulated by HuR. Indeed, HuR is often hijacked in diseases as in psoriatic keratinocytes. In Th17, HuR is responsible for the expression of specific key molecules for psoriasis pathogenesis. It has been shown that 15,16 dihydrotanshinone (DHTS) specifically inhibits the HuR-RNA complex formation. Recently, we have developed a new class of small molecules (named tanshinone mimics, TMs), bearing various substitutions, that modulate the interaction between HuR and its target RNAs in mammalian cells in vitro, more potently than the original DHTS, while displaying more druggable properties. We investigated the role of HuR in psoriasis both at the keratinocytes and at the T-cell levels in patients derived primary cells. HuR is increased in keratinocytes isolated from lesional psoriatic skin compared with healthy subject human keratinocytes, at the protein level. Silencing HuR expression in keratinocytes induced an increase of cells in the G2-M phase, with modulation of differentiation markers. Given the potential pivotal role of HuR in regulating cell proliferation and differentiation, we treated keratinocytes with TM molecules able to selectively bind to HuR while modulating its activity. We demonstrated a dose-dependent inhibition of proliferation both in keratinocytes and in T cells, with modulation of Cyclin B, and an increase of apoptosis at higher concentrations. Psoriasis-derived cells appeared to be more sensitive to treatments. Moreover, psoriatic markers, such as CK16 and EFABP, are decreased by treatments together with modulation of proliferation markers, such as Survivin. Finally, treatments appeared to exert also an immunomodulatory function, increasing the frequency of Th1 cells instead of Th17, modulating cytokine production, such as IL17A, IFNg, CXCL8, and activation of Caspase 1. Further analysis of HuR target molecules is now under evaluation by CLIP-seq analysis on psoriasis patients’ samples. Taken together, these data demonstrate that the inhibition of HuR holds promise for an innovative ground-breaking strategy to limit cytokine release and concomitant blockade of keratinocytes-lymphocytes proliferation and cross-talk.