The class II transactivator (CIITA) is regulated by post-translational modification cross-talk between ERK1/2 phosphorylation, mono-ubiquitination and Lys63 ubiquitination.

Julie E. Morgan,Susanna F. Greer,Ronald L. Shanderson,Nathaniel H. Boyd,Ercan Cacan

doi:10.1042/bsr20150091

Julie E. Morgan, Susanna F. Greer + Show 3 more

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https://doi.org/10.1042/bsr20150091

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Journal: Bioscience reports	Publication Date: Jul 29, 2015
Citations: 13	License type: CC BY 3.0

Affiliation: Georgia State University

Abstract

The class II transactivator (CIITA) is known as the master regulator for the major histocompatibility class II (MHC II) molecules. CIITA is dynamically regulated through a series of intricate post-translational modifications (PTMs). CIITA's role is to initiate transcription of MHC II genes, which are responsible for presenting extracellular antigen to CD4(+) T-cells. In the present study, we identified extracellular signal-regulated kinase (ERK)1/2 as the kinase responsible for phosphorylating the regulatory site, Ser(280), which leads to increased levels of mono-ubiquitination and an overall increase in MHC II activity. Further, we identify that CIITA is also modified by Lys(63)-linked ubiquitination. Lys(63) ubiquitinated CIITA is concentrated in the cytoplasm and following activation of ERK1/2, CIITA phosphorylation occurs and Lys=ubiquitinated CIITA translocates to the nucleus. CIITA ubiquitination and phosphorylation perfectly demonstrates how CIITA location and activity is regulated through PTM cross-talk. Identifying CIITA PTMs and understanding how they mediate CIITA regulation is necessary due to the critical role CIITA has in the initiation of the adaptive immune response.

Highlights

Major histocompatibility class major histocompatibility class II (II) (MHC II) molecules are cell surface glycoproteins which present extracellular antigenic peptides to cluster of differentiation (CD)4 + T-cells [1] in a process critical for activating adaptive immune responses [2]
class II transactivator (CIITA) global ubiquitination and mono-ubiquitination is enhanced when extracellular signal-regulated kinase 1/2 (ERK1/2) are overexpressed and inhibiting endogenous ERK1/2 leads to decreases in global CIITA ubiquitination levels In vivo ubiquitination assay: (A) COS cells were transfected with Myc–CIITA and Flag–ERK1/2
Data shown are cropped images from one IP gel and one lysate gel and are representative of three experiments. (B) Densitometry and quantification of data in Figure 4(A): Densitometry was performed on three independent experiments, +− S.D., *P < 0.05. (C) COS cells were transfected with Myc–CIITA and indicated samples were treated with U0126 (MEK specific inhibitor) at time of transfections

Summary

Introduction

Major histocompatibility class II (MHC II) molecules are cell surface glycoproteins which present extracellular antigenic peptides to cluster of differentiation (CD)4 + T-cells [1] in a process critical for activating adaptive immune responses [2]. MHC II expression is tightly regulated by transcriptional processes [3], initiation of which require the class II transactivator (CIITA) to be recruited to the MHC II promoter [4]. CIITA is a non-DNA-binding cofactor that binds to the components of an enhanceasome complex to initiate MHC II transcription [4]. CIITA is a master regulator of MHC class II transcription and is expressed from three separate promoters, pI, pIII and pIV, each of which yields cell-specific isoforms [5]. CIITA isoform I (IF1) is primarily expressed in dendritic cells and macrophages, isoform III (IF3) is constitutively expressed in B-cells and is interferon (IFN)-γ inducible [6,7]. IF4 is expressed from all nucleated cells and is regulated through IFN-γ induction [7]

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