Periodic Reporting for period 2 - PHYRIST (Physiological roles of the Ribotoxic Stress Response)
Période du rapport: 2021-12-01 au 2023-05-31
All synthesis of proteins occurs on ribosomes, and impairment of this process constitutes cellular stress.
The ribotoxic stress response (RSR) is one of three cellular maintenance systems that survey the structural and functional integrity of ribosomes. When presented with impaired ribosomes, the kinase ZAK-alpha phosphorylates and activates the kinases p38 and JNK to initiate inflammatory responses and/or induce programmed cell death. In addition, signaling though p38 and JNK has the potential to impact on cell differentiation, stress adaptation and metabolic regulation. However, despite decades of research into the RSR, the physiological relevance of the underlying pathway in whole organisms is unknown. In this project, I hypothesize that ribosomes are central cellular stress sensors and that the RSR constitutes a general stress response system. I aim to uncover the physiological and pathological implications of RSR impairment in diverse model organisms, such as mice, zebrafish and nematodes.
In one line of investigation, I am elucidating the connections between UV radiation to the skin and RSR-mediated cell death and inflammatory responses. These responses are relevant to many natural and pathological reactions in the skin, incl. sunburn, skin cancer development and tanning. I am also working towards understanding the spectrum of physiologically relevant perturbations that impair ribosomal translation and activates the RSR within our body. Finally, my work is focused on unravelling the molecular mechanism(s) underlying ribotoxic stress sensing by ZAK-alpha.
In sum, PHYRIST will yield the first detailed insight into the in vivo relevance of the ribotoxic stress response.
The ribotoxic stress response (RSR) is one of three cellular maintenance systems that survey the structural and functional integrity of ribosomes. When presented with impaired ribosomes, the kinase ZAK-alpha phosphorylates and activates the kinases p38 and JNK to initiate inflammatory responses and/or induce programmed cell death. In addition, signaling though p38 and JNK has the potential to impact on cell differentiation, stress adaptation and metabolic regulation. However, despite decades of research into the RSR, the physiological relevance of the underlying pathway in whole organisms is unknown. In this project, I hypothesize that ribosomes are central cellular stress sensors and that the RSR constitutes a general stress response system. I aim to uncover the physiological and pathological implications of RSR impairment in diverse model organisms, such as mice, zebrafish and nematodes.
In one line of investigation, I am elucidating the connections between UV radiation to the skin and RSR-mediated cell death and inflammatory responses. These responses are relevant to many natural and pathological reactions in the skin, incl. sunburn, skin cancer development and tanning. I am also working towards understanding the spectrum of physiologically relevant perturbations that impair ribosomal translation and activates the RSR within our body. Finally, my work is focused on unravelling the molecular mechanism(s) underlying ribotoxic stress sensing by ZAK-alpha.
In sum, PHYRIST will yield the first detailed insight into the in vivo relevance of the ribotoxic stress response.
For the first two and a half years of the project period, we have made significant progress along all of the major lines of investigation. First, we have undertaken a careful analysis of the skin reactions to UV-irradiation in our ZAK knockout (KO) mouse model. These studies highlight the central and early role of the RSR in mounting inflammatory responses and activating programmed cell death mechanisms in the skin upon UV-irradiation and sun light exposure. Second, we have discovered that the RSR constitutes a new and surprising node for metabolic regulation. This is evident from the lean phenotype of ZAK KO mice and altered insulin signaling and stress hormone production upon feeding a leucine-deficient diet. Third, we have also made new discoveries in relation to the activation mechanism for ZAK-alpha. Fourth, and as an unexpected outcome of our work, we have found a role for the kinase ZAK-beta, which is encoded as a splice variant of the Zak gene in mammals. This version of the ZAK protein does not bind the ribosome and sense ribotoxic stress, rather it is associated with the sensing of mechanical load in muscles undergoing contraction.
The association between the RSR and metabolic regulation is an important new avenue for both the field of ribosome biology and the field of metabolism. Our first paper on the subject highlights ribosomal impairment as a metabolic stress signal that is read and communicated by ZAK-alpha and the RSR. We are currently pursuing similar lines of enquiry by subjecting our mice to additional experimental feeding regimens. I expect that we will publish at least one more paper on the subject before the end of the project period.