HuR activity modulation as a novel anti-psoriatic pharmacological strategy

HuR is one of the most studied RNA Binding Proteins (RBPs involved in post-transcriptional regulation, capable of binding mRNA via AU-rich elements (AREs) in 3’-untranslated regions (3’-UTRs). HuR primarily localizes in the nucleus, however, following external stimuli (e.g., stress or inflammation), it translocates into the cytoplasm. It is ubiquitously expressed and acts as a pivotal regulator of cellular stability; its dysregulation is therefore strongly associated with the progression of cancer and inflammatory pathologies. Among them, psoriasis is a chronic inflammatory skin disease characterized by hyperproliferative keratinocytes and an activated immune response that leads to the release of pro-inflammatory cytokines in a self-perpetuating cycle. Several cytokines and psoriatic hallmark mRNAs contain ARE elements, making them potential HuR targets; in fact, HuR could bind and stabilize these transcripts, thereby contributing to an inflammatory state that could be associated with psoriasis progression. Following this rationale, we demonstrated in patient-derived primary cells that HuR plays a key role in psoriasis development by regulating not only inflammatory cytokines but also keratinocyte proliferation markers. Specifically, it stabilizes markers such as S100A7 and EFABP in primary psoriatic keratinocytes, as well as inflammation-related transcripts, including IL-6 and IL-1β mRNAs in psoriasis-like HaCaT cells and keratinocytes. Interestingly, enhanced Cross-link ImmunoPrecipitation sequencing (eCLIP-seq) in psoriasis-like HaCaT cells revealed novel HuR targets, including ATF2, H3C6 and RAB27A mRNAs, expanding the functional activity of this protein in keratinocytes. Furthermore, we modulated HuR activity using small molecules previously identified as protein-RNA interaction inhibitors called Tanshinone mimics (TMs), such as TM11 and TM7nred. In the context of psoriasis, these molecules reduced keratinocyte proliferation and the expression of psoriasis-associated proteins (Cyclin B, Survivin, S100A7, eFABP). In addition, TM11 reduced Psoriasis Area and Severity Index (PASI) score, systemic inflammation and histological alterations in Imiquimod-treated mice. To further elucidate the effect of TM11 in a standardized cellular model resembling human skin, the drug was tested in an ex vivo 3D skin model derived from human biopsies and induced to develop a psoriasis-like immune response. In this context, TM11 restored epidermal morphology, decreased Ki-67-positive cells, and lowered IL-17AF and IFNɣ secretion. These data elucidate the TM11-mediated HuR activity modulation, resulting in keratinocyte hyperproliferation reduction and skin homeostasis restoration. Overall, this thesis highlights the central role of HuR in psoriasis and the potential of its modulation as a new therapeutic strategy. To further expand these therapeutic prospects, in parallel with the study of TMs, we identified a novel class of HuR inhibitors through DNA-Encoded Library (DEL) screening. This approach led to the identification of WuXi-7 as a hit compound, which subsequently served as the scaffold for the synthesis of a series of optimized derivatives. Through REMSA screening, we identified three new analogs, SH33, SH35 and SH48, which can efficiently disrupt the HuR-mRNA complex. These molecules represent a novel chemical scaffold for targeting this RBP and could be rationally explored in psoriatic models as additional proof-of-principle.