Mechanisms of HuR Overexpression in Asthmatic Endotypes

Abstract
Despite extensive research, asthma remains a difficult to treat disease with staggering economic costs.
Mechanisms in different asthmatic endotype are poorly understood. Posttranscriptional gene regulation by RNA-
binding proteins (RBPs) and microRNAs (miRNAs) is increasingly recognized as important control mechanisms
for pro-inflammatory genes but is understudied. RBPs, such as HuR (Elavl1), tristetraprolin (TTP) family
members which bind to mRNA AU-rich elements (ARE), play critical roles in regulating mRNA stability and
expression of key pro-inflammatory genes in asthma. HuR is a stabilizer RBP, whereas TTP family members are
destabilizer RBPs. Due to the discordance between steady-state mRNA levels and protein, purely transcriptomic
approaches may overlook critical inflammatory genes regulated by RBPs such as HuR and TTP. Yet, much of
immunity and inflammation is controlled at the posttranscriptional level by RBPs and miRNAs. Many cytokine
genes in CD4+ T cells are controlled by the balance between HuR and TTP family members. The field cannot
move forward unless we better understand how RBPs posttranscriptionally regulate pro-inflammatory gene
expression in different asthmatic endotypes. Our long-term goal is to understand posttranscriptional gene
regulation in different endotypes of asthmatic airway inflammation. The objective of this application, which is our
next step in pursuit of that goal, is to determine how HuR and TTP family members competitively regulate HuR
expression, which in turn controls CD4+ T produced cytokines in asthma. Our central hypothesis is that HuR
overproduction in type 2 high asthma is driven by an imbalance between stabilizing and destabilizing RBPs
acting upon Elavl1 mRNA to affect its stability and translation. Our data indicate that HuR is over-expressed in
type 2 high asthmatic CD4+ T cells, compared with normal controls and non-type 2 high. Furthermore, we have
shown that conditional HuR KO in T cells significantly ameliorates allergen-induced lung inflammation in murine
models. We have also demonstrated that HuR inhibition blocks Th2/Th17 secretion in asthmatic CD4+ T cells.
Up to the present, the field has focused mostly on downstream HuR targets genes. In contrast, HuR regulation
is not as well understood. The rationale for this research is that the proposed research will enable us to identify
molecular mechanisms which drive HuR over-production in the context of type 2 high asthmatic lung
inflammation. We plan to test the central hypothesis and accomplish these objectives by the following two specific
aims: 1) Determine normal mechanisms of HuR expression in airway inflammation; 2) Determine molecular
mechanisms underlying HuR dysregulation in type 2 high asthma. At the completion of the proposed research,
our expected outcomes are to identify how HuR and TTP cooperate to normally control HuR expression and how
they become dysfunctional in type 2 high asthmatic CD4+ T cells. These results are expected to have a positive
impact on the field because it will further define molecular mechanisms and provide opportunities to develop
novel therapies to treat asthma.

Grant Number: 5R21AI173487-02
NIH Institute/Center: NIH
Principal Investigator: ULUS ATASOY