KLHDC10 Activates ASK1 by Suppressing PP5

Reactive oxygen species (ROS)-induced activation of Apoptosis signal-regulating kinase 1 (ASK1) plays crucial roles in oxidative stress-mediated cell death through the activation of the JNK and p38 MAPK pathways. However, the regulatory mechanism of ASK1 in the oxidative stress response remains to be elucidated. Here, we identified the kelch repeat protein, Slim, as an activator of ASK1 through a Drosophila misexpression screen. We also performed a proteomics screen and revealed that Kelch domain containing 10 (KLHDC10), a mammalian ortholog of Slim, interacted with Protein phosphatase 5 (PP5), which has been shown to inactivate ASK1 in response to ROS. KLHDC10 bound to the phosphatase domain of PP5 and suppressed its phosphatase activity. Moreover, KLHDC10 was required for H2O2-induced sustained activation of ASK1 and cell death in Neuro2A cells. These findings suggest that Slim/KLHDC10 is an activator of ASK1, contributing to oxidative stress-induced cell death through the suppression of PP5

Vasculature-driven stem cell population coordinates tissue scaling in dynamic organs

Stem cell (SC) proliferation and differentiation organize tissue homeostasis. However, how SCs regulate coordinate tissue scaling in dynamic organs remain unknown. Here, we delineate SC regulations in dynamic skin. We found that interfollicular epidermal SCs (IFESCs) shape basal epidermal proliferating clusters (EPCs) in expanding abdominal epidermis of pregnant mice and proliferating plantar epidermis. EPCs consist of IFESC-derived Tbx3⁺–basal cells (Tbx3⁺-BCs) and their neighboring cells where Adam8–extracellular signal–regulated kinase signaling is activated. Clonal lineage tracing revealed that Tbx3⁺-BC clones emerge in the abdominal epidermis during pregnancy, followed by differentiation after parturition. In the plantar epidermis, Tbx3⁺-BCs are sustained as long-lived SCs to maintain EPCs invariably. We showed that Tbx3⁺-BCs are vasculature-dependent IFESCs and identified mechanical stretch as an external cue for the vasculature-driven EPC formation. Our results uncover vasculature-mediated IFESC regulations, which explain how the epidermis adjusts its size in orchestration with dermal constituents in dynamic skin

Regulation of NR4A nuclear receptors by p38

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

ASK1 restores the antiviral activity of APOBEC3G by disrupting HIV-1 Vif-mediated counteraction

APOBEC3G (A3G) is an innate antiviral restriction factor that strongly inhibits the replication of human immunodeficiency virus type 1 (HIV-1). An HIV-1 accessory protein, Vif, hijacks the host ubiquitin-proteasome system to execute A3G degradation. Identification of the host pathways that obstruct the action of Vif could provide a new strategy for blocking viral replication. We demonstrate here that the host protein ASK1 (apoptosis signal-regulating kinase 1) interferes with the counteraction by Vif and revitalizes A3G-mediated viral restriction. ASK1 binds the BC-box of Vif, thereby disrupting the assembly of the Vif-ubiquitin ligase complex. Consequently, ASK1 stabilizes A3G and promotes its incorporation into viral particles, ultimately reducing viral infectivity. Furthermore, treatment with the antiretroviral drug AZT (zidovudine) induces ASK1 expression and restores the antiviral activity of A3G in HIV-1-infected cells. This study thus demonstrates a distinct function of ASK1 in restoring the host antiviral system that can be enhanced by AZT treatment

Transient elevation of cytoplasmic calcium ion concentration at a single cell level precedes morphological changes of epidermal keratinocytes during cornification

Epidermal keratinocytes achieve sequential differentiation from basal to granular layers, and undergo a specific programmed cell death, cornification, to form an indispensable barrier of the body. Although elevation of the cytoplasmic calcium ion concentration ([Ca²⁺]i) is one of the factors predicted to regulate cornification, the dynamics of [Ca²⁺]i in epidermal keratinocytes is largely unknown. Here using intravital imaging, we captured the dynamics of [Ca²⁺]i in mouse skin. [Ca²⁺]i was elevated in basal cells on the second time scale in three spatiotemporally distinct patterns. The transient elevation of [Ca²⁺]i also occurred at the most apical granular layer at a single cell level, and lasted for approximately 40 min. The transient elevation of [Ca²⁺]i at the granular layer was followed by cornification, which was completed within 10 min. This study demonstrates the tightly regulated elevation of [Ca²⁺]i preceding the cornification of epidermal keratinocytes, providing possible clues to the mechanisms of cornification

Tbx3-dependent amplifying stem cell progeny drives interfollicular epidermal expansion during pregnancy and regeneration

妊娠期に腹部の皮膚が広がる仕組みの一端をマウスで解明. 京都大学プレスリリース. 2017-09-13.The skin surface area varies flexibly in response to body shape changes. Skin homeostasis is maintained by stem cells residing in the basal layer of the interfollicular epidermis. However, how the interfollicular epidermal stem cells response to physiological body shape changes remains elusive. Here, we identify a highly proliferative interfollicular epidermal basal cell population in the rapidly expanding abdominal skin of pregnant mice. These cells express Tbx3 that is necessary for their propagation to drive skin expansion. The Tbx3+ basal cells are generated from Axin2+ interfollicular epidermal stem cells through planar-oriented asymmetric or symmetric cell divisions, and express transit-amplifying cell marker CD71. This biased division of Axin2+ interfollicular epidermal stem cells is induced by Sfrp1 and Igfbp2 proteins secreted from dermal cells. The Tbx3+ basal cells promote wound repair, which is enhanced by Sfrp1 and Igfbp2. This study elucidates the interfollicular epidermal stem cell/progeny organisation during pregnancy and suggests its application in regenerative medicine