P38 MAPKs regulate the expression of genes in the dopamine synthesis pathway through phosphorylation of NR4A nuclear receptors

Yusuke Sekine,Haruka Oguchi,Takeshi Toyoda,Hidenori Ichijo,Takashi Funatsu,Kazuto Kobayashi,Shuichi Takagahara,Erina Kuranaga,Makoto Tsunoda,Norio Matsuki,Hiroshi Nomura,Takeshi Watanabe,Ryo Hatanaka,Masayuki Miura,Takuya Noguchi,Kohsuke Takeda,Isao Naguro

doi:10.1242/jcs.085902

Abstract

In Drosophila, the melanization reaction is an important defense mechanism against injury and invasion of microorganisms. Drosophila tyrosine hydroxylase (TH, also known as Pale) and dopa decarboxylase (Ddc), key enzymes in the dopamine synthesis pathway, underlie the melanin synthesis by providing the melanin precursors dopa and dopamine, respectively. It has been shown that expression of Drosophila TH and Ddc is induced in various physiological and pathological conditions, including bacterial challenge; however, the mechanism involved has not been fully elucidated. Here, we show that ectopic activation of p38 MAPK induces TH and Ddc expression, leading to upregulation of melanization in the Drosophila cuticle. This p38-dependent melanization was attenuated by knockdown of TH and Ddc, as well as by that of Drosophila HR38, a member of the NR4A family of nuclear receptors. In mammalian cells, p38 phosphorylated mammalian NR4As and Drosophila HR38 and potentiated these NR4As to transactivate a promoter containing NR4A-binding elements, with this transactivation being, at least in part, dependent on the phosphorylation. This suggests an evolutionarily conserved role for p38 MAPKs in the regulation of NR4As. Thus, p38-regulated gene induction through NR4As appears to function in the dopamine synthesis pathway and may be involved in immune and stress responses.

Highlights

Melanin is a widespread pigment found in the skin, hair and eyes of animals, protecting them from harmful environmental stimuli
We constructed an expression vector for Drosophila ASK1DN, lacking the ASK1 N-terminal regulatory domain, which is similar in its primary structure to the mammalian ASK1DN that has been shown to act in a constitutively active manner (Mizumura et al, 2006; Takeda et al, 2000)
We found that p38b was activated by coexpression with ASK1DN, we could not evaluate the activation state of p38c because of the lack of the TGY motif

Summary

Introduction

Melanin is a widespread pigment found in the skin, hair and eyes of animals, protecting them from harmful environmental stimuli. Rapid deposition of melanin at the wound site prevents the loss of hemolymph and leads to killing of the invading microorganisms by toxic intermediates, such as reactive oxygen species, that are produced during the melanin biosynthesis. In Drosophila, tyrosine-derived catecholamines, such as dopa and dopamine, serve as the precursors of melanin, which constitutes the black and brown pigments in the cuticle and wing (Wittkopp et al, 2003). Drosophila tyrosine hydroxylase (TH, known as Pale) catalyses the oxidation of tyrosine to dopa, which is the first and rate-limiting step in dopamine biosynthesis. Dopa decarboxylase (Ddc) converts dopa into dopamine. Some fractions of dopa and dopamine are oxidized by phenoloxidase (PO) in the hemolymph and converted into quinones, which are polymerized non-enzymatically to form dopa- and dopamine-melanin, respectively

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Conclusion