Poly(rC) binding protein 2 acts as a negative regulator of IRES-mediated translation of Hr mRNA

Jeong-Ki Kim,Jee-Hyun Choi,Jongkeun Park,Eunmin Kim,Injung Kim,Hwa-Young Lee,Sungjoo Kim Yoon,Keonwoo Choi

doi:10.1038/emm.2017.262

Abstract

During the hair follicle (HF) cycle, HR protein expression is not concordant with the presence of the Hr mRNA transcript, suggesting an elaborate regulation of Hr gene expression. Here we present evidence that the 5′ untranslated region (UTR) of the Hr gene has internal ribosome entry site (IRES) activity and this activity is regulated by the binding of poly (rC) binding protein 2 (PCBP2) to Hr mRNA. Overexpression and knockdown of PCBP2 resulted in a decrease in Hr 5′ UTR IRES activity and an increase in HR protein expression without changing mRNA levels. We also found that this regulation was disrupted in a mutant Hr 5′ UTR that has a mutation responsible for Marie Unna hereditary hypotrichosis (MUHH) in both mice and humans. These findings suggest that Hr mRNA expression is regulated at the post-transcriptional level via IRES-mediated translation control through interaction with PCPB2, but not in MUHH.

Highlights

Because the effect of the upstream open reading frames (uORFs) on the synthesis of the HR protein has not been studied, we investigated the function of the Hr 5′ untranslated region (UTR) on HR protein expression using several mouse Hr mutant constructs
To elucidate a mechanism by which Hr mRNA overcomes the repression of its activity via its 5′ UTR, we hypothesized that the Hr 5′ UTR had internal ribosome entry site (IRES) activity that allowed for the translation of HR to be initiated directly and in a capindependent manner without inhibition by uORFs
Mutation of Hr 5′ UTR suppressed the regulation of Hr 5′ UTR by poly (rC) binding protein 2 (PCBP2) in Marie Unna hereditary hypotrichosis (MUHH) we investigated whether this IRES-mediated translational control for HR protein could affect mutant Hr 5′ UTR, which has the mutation corresponding to MUHH

Summary

Introduction

Hairless (HR) is a transcriptional co-factor that regulates downstream gene expression as a co-repressor of nuclear receptors, including thyroid hormone receptors, retinoic acid receptors and vitamin D receptors.[1,2,3,4] The Hr gene is expressed mainly in the brain and skin and has been shown to be associated with the Wnt signaling pathway in hair follicle (HF) development.[4,5,6,7] In humans, mutations of the HR gene cause hair loss disorders, including alopecia universalis congenita, atrichia papular lesions and Marie Unna hereditary hypotrichosis (MUHH).[8,9,10] many Hr mutant mice, such as Hrhr, Hrrh, Hrm1Enu and HrHp, have been used as mouse models for human hair loss disorders.[11,12,13] The numerous mutations of Hr that manifest an abnormal hair phenotype in humans and mice suggest that the function of the HR protein is critically important in HF development. It is interesting to note that both the lack and excess of HR result in the hair loss phenotype. We reported that overexpression of the HR protein caused hair loss disease in humans (MUHH) and mice (HrHp). We demonstrated that the HrHp mice had a regulatory mutation in the Hr 5′ untranslated region (UTR) resulting in overexpression of the HR protein, excessive induction of Wnt signaling,[14] and abnormal formation of HF structures.[15] This evidence indicated that tight regulation of HR expression levels was important in HF development and normal hair cycling

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Conclusion