Abstract: 【Abstract】 Objective To determine the expression of Brahma-related gene 1 （BRG1） in cutaneous squamous cell carcinoma （cSCC） tissues and cells, and to investigate molecular mechanisms underlying the regulatory effect of its interaction with activating transcription factor 2 （ATF2） on the proliferation, migration and invasion of cSCC cells. Methods From 2015 to 2021, 66 paraffin-embedded actinic keratosis （AK） tissue samples and 80 paraffin-embedded cSCC （including squamous cell carcinoma in situ） tissue samples were collected from the Department of Dermatology, Affiliated Hospital 2 of Nantong University, and the diagnoses of all the cases were confirmed histopathologically; at the same time, 35 paraffin-embedded normal skin tissue samples obtained by cosmetic surgery served as normal control group. Immunohistochemical staining was performed to determine the BRG1 expression in cSCC, AK, and normal skin tissues, and correlations between BRG1 expression and clinicopathological parameters of cSCC patients were analyzed. Fresh tissue samples were collected from 12 cSCC patients and 12 healthy controls, and cSCC cell lines A431 and Scl-1 and a human immortalized keratinocyte cell line HaCaT were routinely cultured; real-time fluorescence-based quantitative PCR （qRT-PCR） was performed to determine the mRNA expression of BRG1 in tissues and cells, and co-immunoprecipitation assay and cellular immunofluorescence staining were conducted to analyze the interaction between BRG1 and ATF2. The expression of BRG1 （BRG1 siRNA1 - 5 groups） and ATF2 （ATF2-shRNA group） in A431 and Scl-1 cells was knocked down by RNA interference, and cells transfected with negative control siRNA or shNC served as controls （control siRNA group and shNC group, respectively）, cell counting kit-8 （CCK8） assay, colony formation assay, cell scratch assay, and Transwell assay were conducted to evaluate effects of knocking down BRG1 and ATF2 on the proliferation, migration, and invasion of cSCC cells. Comparisons of measurement data among multiple groups were conducted using one-way analysis of variance, and multiple comparisons were conducted using Dunnett-t test. Results Immunohistochemical staining showed that the expression intensity of BRG1 protein was significantly lower in the cSCC and AK tissues than in the normal skin tissues （χ2 = 44.40, P < 0.001）. qRT-PCR showed that the mRNA expression level of BRG1 was significantly lower in the cSCC tissues （1.345 ± 0.956） than in the normal skin tissues （2.499 ± 1.501, t = 2.25, P = 0.035）, and also significantly lower in A431 and Scl-1 cells （0.041 ± 0.002, 0.026 ± 0.003, respectively） than in HaCaT cells （0.135 ± 0.033, t = 4.95, 5.73, P = 0.008, 0.005, respectively）. The low expression of BRG1 was associated with tumors at sun-exposed sites （P = 0.041）, low tumor differentiation （P = 0.001）, and high Broder′s grade （P < 0.001） in the cSCC patients. In both A431 cells and Scl-1 cells, the BRG1 siRNA1 group and BRG1 siRNA2 group showed significantly increased numbers of cell colonies, migratory cells and invasive cells, as well as cell migration rates compared with the control siRNA group （all P < 0.05）. Co-immunoprecipitation assay showed that BRG1 protein could bind to ATF2 protein in A431 and Scl-1 cells, and immunofluorescence staining showed that the two proteins were co-localized; compared with the control siRNA group, the BRG1 siRNA1 group （both A431 and Scl-1 cells） and BRG1 siRNA2 group （A431 cells） both showed increased phosphorylation and activation of ATF2 （all P < 0.05）; in both A431 cells and Scl-1 cells, the shATF2 group showed significantly decreased numbers of cell colonies （both P = 0.001）, cellular proliferative activity at 24 - 96 hours （all P < 0.001）, and numbers of migratory cells and invasive cells compared with the shNC group （all P ≤ 0.001）. Conclusion BRG1 was lowly expressed in the cSCC and AK tissues, and could inhibit the proliferation, migration, and invasion of cSCC cells; ATF2 could promote the proliferation, migration, and invasion of cSCC cells; BRG1 may exert an anti-tumor effect by interacting with ATF2 protein and inhibiting phosphorylation-dependent activation of ATF2.

Key words: Carcinoma, squamous cell, Skin, Keratosis, actinic, BRG1, ATF2, SWI/SNF complex, Chromatin remodeling