Bik promotes proteasomal degradation to control low-grade inflammation
Yohannes A. Mebratu, … , Scott Randell, Yohannes Tesfaigzi
Yohannes A. Mebratu, … , Scott Randell, Yohannes Tesfaigzi
Published December 19, 2023
Citation Information: J Clin Invest. 2024;134(4):e170594. https://doi.org/10.1172/JCI170594.
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Research Article Inflammation

Bik promotes proteasomal degradation to control low-grade inflammation

Abstract

Although chronic low-grade inflammation does not cause immediate clinical symptoms, over the longer term, it can enhance other insults or age-dependent damage to organ systems and thereby contribute to age-related disorders, such as respiratory disorders, heart disease, metabolic disorders, autoimmunity, and cancer. However, the molecular mechanisms governing low-level inflammation are largely unknown. We discovered that Bcl-2–interacting killer (Bik) deficiency causes low-level inflammation even at baseline and the development of spontaneous emphysema in female but not male mice. Similarly, a single nucleotide polymorphism that reduced Bik levels was associated with increased inflammation and enhanced decline in lung function in humans. Transgenic expression of Bik in the airways of Bik-deficient mice inhibited allergen- or LPS-induced lung inflammation and reversed emphysema in female mice. Bik deficiency increased nuclear but not cytosolic p65 levels because Bik, by modifying the BH4 domain of Bcl-2, interacted with regulatory particle non-ATPase 1 (RPN1) and RPN2 and enhanced proteasomal degradation of nuclear proteins. Bik deficiency increased inflammation primarily in females because Bcl-2 and Bik levels were reduced in lung tissues and airway cells of female compared with male mice. Therefore, controlling low-grade inflammation by modifying the unappreciated role of Bik and Bcl-2 in facilitating proteasomal degradation of nuclear proteins may be crucial in treating chronic age-related diseases.

Authors

Yohannes A. Mebratu, Jane T. Jones, Congjian Liu, Zerihun H. Negasi, Mizanur Rahman, Joselyn Rojas-Quintero, George T. O’Connor, Wei Gao, Josée Dupuis, Michael H. Cho, Augusto A. Litonjua, Scott Randell, Yohannes Tesfaigzi

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Figure 5

Bik, localized to nuclear domains of the cell, reduces nuclear p65 by binding to Bcl-2.

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Bik, localized to nuclear domains of the cell, reduces nuclear p65 by bi...
(A) Primary HAECs and A549 cells were immunostained for Bik protein and analyzed by fluorescent microscopy for the localization of Bik protein. Original magnification, ×1,200. (B) Cytosolic and nuclear extracts from HEK293T and HAECs were analyzed for the localization of p65, Bik, and Bcl-2 by Western blotting. (C) HEK293T cells were transfected with EV or Bcl-2 plasmid, and protein lysates were analyzed for Bcl-2 and p65 levels by Western blotting. (D) WT and CRISPR/cas9 Bik-knockout HEK293T cells were transfected with plasmids expressing WT Bcl-2. Forty-eight hours later, nuclear lysates were analyzed for levels of p65 and Bcl-2 by Western blotting. The bar graph on the right-hand side shows densitometry (p65 fold change) of the Western blot from 3 independent experiments. (E) CRISPR/Cas9 Bcl-2–knockout cells were transfected with EV, WT, or mutant triple–flag-tagged Bcl-2. Forty-eight hours later, nuclear lysates were analyzed for the expression levels of p65 using Western blotting, nuclear lysates were immunoprecipitated using anti-p65 or Bcl-2 antibodies, and the Ips were probed for flag–Bcl-2 and p65. (F) Bik CRISPR/Cas9 knockout cells were transfected with EV or plasmids expressing WT or phosphorylation-mutant Bik constructs. Forty-eight hours later, cytosolic and nuclear lysates were analyzed for p65 levels by Western blotting. Two-tailed Student’s t test was used to compare between 2 groups, and grouped results were analyzed using 2-way ANOVA. Data are represented as mean ± SEM. *P < 0.05.