Apoptosis signal-regulating kinase 1 (ASK1) is a member of the mitogen-activated protein kinase kinase kinase family, which activates c-Jun N-terminal kinase and p38 in response to a diverse array of stresses such as oxidative stress, endoplasmic reticulum stress and calcium influx. In the past decade, various regulatory mechanisms of ASK1 have been elucidated, including its oxidative stressdependent activation. Recently, it has emerged that ASK family proteins play key roles in cancer, cardiovascular diseases and neurodegenerative diseases. In this review, we summarize the recent findings on ASK family proteins and their implications in various diseases.

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Changes in the osmolality of body fluids pose a serious danger to cells and living organisms, which have developed cellular systems to sense and respond to osmotic stress and to maintain homoeostasis of body fluid. However, these processes are incompletely understood in mammals. Here we show that apoptosis signal-regulating kinase 3 (ASK3) is predominantly expressed in the kidney and alters its kinase activity bidirectionally in response to osmotic stress. We further demonstrate that ASK3 interacts with WNK1, mutation in which causes an inherited form of hypertension in humans. Knockdown of Ask3 by short interfering RNA enhances the activation of the WNK1-SPAK/OSR1 signalling pathway. Moreover, Ask3 knockout mice exhibit a hypertensive phenotype, in addition to hyperactivation of SPAK/OSR1 in renal tubules. Our results suggest that ASK3 is a unique bidirectional responder to osmotic stress and that it has a role in the control of blood pressure as an upstream suppressor of the WNK1-SPAK/OSR1 signalling pathway.

A wide variety of cell death mechanisms, such as ferroptosis, have been proposed in mammalian cells, and the classification of cell death attracts global attention because each type of cell death has the potential to play causative roles in specific diseases. However, the precise molecular mechanisms leading to cell death are poorly understood, particularly in ferroptosis. Here, we show that continuous severe cold stress induces ferroptosis and the ASK1-p38 MAPK pathway in multiple cell lines. The activation of the ASK1-p38 pathway is mediated by critical determinants of ferroptosis: MEK activity, iron ions, and lipid peroxide. The chemical compound erastin, a potent ferroptosis inducer, also activates the ASK1-p38 axis downstream of lipid peroxide accumulation and leads to ASK1-dependent cell death in a cell type-specific manner. These lines of evidence provide mechanistic insight into ferroptosis, a type of regulated necrosis.