Brahma-related gene 1 regulates the proliferation of alveolar type II epithelial cells via the JAK1/2-PI3K/AKT signaling pathway
Authors: Xu Maozhu , Qiu Huijun , Ruan Lingyin , Zhang Linghuan , Yang Lili , Fu Zhou , Zou Wenjing 
Published: November 2022

Abstract
Background
Alveolar type II epithelial cells (AECIIs), a crucial part of the alveolar epithelium, can secrete surfactant-associated proteins and act as progenitor cells of the alveoli. The number of AECIIs in lung tissues is closely related to the pathogenesis and pathological process of numerous lung diseases. Brahma-related geng1 (Brg1), a catalytic subunit of ATPase, is a core component of the mammalian switch/sucrose non-fermentable (SWI/SNF) ATP-dependent chromatin-remodeling complex, which achieves chromosome recombination and further regulates gene expression in an ATP-dependent manner. Brgl plays a pivotal role in regulating cell differentiation, proliferation, and apoptosis. Unfortunately, almost no research exists on the relationship between Brg1 and AECIIs. Therefore, we aimed to investigate the effect of Brg1 on the quantity of AECIIs as well as the possible mechanisms.
Methods
C57BL/6 mice with the Brg1 gene specifically knocked out in AECII epithelial cells (Brg1fl/fl mice) were constructed to analyze the effect of brg1 gene expression on the number of AECIIs in vivo. The number of ACEIIs was detected and compared in the Brg1fl/fl group and wild-type (WT) group using immunohistochemistry, flow cytometry, and immunofluorescence. The Brg1 gene in immortalized mouse pulmonary alveolar type II (ImpacII) cells was knocked down using lentiviral vectors. The migration and invasion of ImpacII were observed using cell scratch assay and transwell migration assay. The proliferation of ImpacII was monitored using the cell clone assay, CCK-8 cell proliferation assay, and cell cycle assay. The proliferation-related proteins including Ki67, p-JAK1/2/JAK1/2, p-STAT6/STAT6, p-PI3K/PI3K, and p-AKT/AKT were detected using Western blot and immunofluorescence in ImpacII cells. To explore the specific molecular mechanism of Brg1 regulating ImpacII proliferation, the binding sequences of Brg1 in ImpacII cells were sought using chromatin immunoprecipitation-sequence (CHIP-seq) and further confirmed by chromatin immunoprecipitation-qPCR (CHIP-qPCR). The interactive relationship between JAK1/2 and PI3K was verified by co-immunoprecipitation (Co-IP) assay.
Results
Knocking out brg1 facilitated the proliferation of AECIIs in vivo. Knocking down brg1 induced the proliferation in association with the migration and invasion of ImpacII in vitro. Mechanistically, knocking down brg1 activated the JAK1/2-PI3K/AKT signaling pathway and induced the expression of proliferation-related protein Ki67. Furthermore, CHIP-seq and CHIP-qPCR results showed that Brg1 could bind to the JAK1/2 promoter region and regulate the activity of the JAK1/2-PI3K/AKT signaling pathway. Co-IP confirmed that JAK1/2 interacted with PI3K.
Conclusion
Knocking out Brg1 promoted the proliferation, migration, and invasion of AECIIs via the JAK1/2-PI3K/AKT signaling pathway. This represents a potential therapeutic target and a novel prognostic indicator in various pulmonary diseases.