[SRF promotes the progression of lung adenocarcinoma by regulating lncRNA FGD5-AS1]

Objective: To explore the role and mechanism of serum response factor (SRF) and lncRNA FGD5-AS1 in lung adenocarcinoma (LUAD). Methods: The plasma and tissue wax of LUAD patients treated in Tangshan People's Hospital from 2020 to 2022 and the plasma of healthy people were collected. The expression of SRF in LUAD tissues and cells, and the expression of lncRNA FGD5-AS1 in LUAD tissues, plasma and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The expression levels of SRF and lncRNA FGD5-AS1 in LUAD tissue microarray were detected by immunohistochemistry and in situ hybridization. LUAD cells A549, H1299 and H1975 were cultured in vitro and divided into si-NC and si-SRF groups, si-NC and si-lncRNA FGD5-AS1 groups, pcDNA3.1 and lncRNA FGD5-AS1 groups, si-NC+pcDNA3.1/si-SRF+pcDNA3.1/si-SRF+lncRNA FGD5-AS1 groups. The effects of the above groups on the proliferation, invasion and migration of LUAD cells were detected by CCK-8, cloning formation, EdU, Transwell and scratch test. The JASPAR database was used to predict the downstream lncRNA FGD5-AS1 that can be regulated by SRF; double luciferase experiment, chromatin Immunoprecipitation (CHIP) and electrophoretic mobility shift assay (EMSA) experiment were used to verify the regulatory effect between SRF and lncRNA FGD5-AS1, and the subcutaneous tumorigenesis experiment in nude mice was used to detect the effects of cells that stably knock down SRF and stably overexpress lncRNA FGD5-AS1 on the growth of transplanted tumors. Results: The results of immunohistochemistry showed that the mean optical density of SRF in LUAD tissues (1.49±0.33) was higher than that in adjacent tissues (1.00±0.00, P＜0.001). The expression level of SRF in paraffin tissues of LUAD patients was higher than that in normal tissues adjacent to cancer (P=0.037). CCK-8, cloning, scratch and Transwell experiments showed that knockdown SRF could inhibit the proliferation, migration and invasion of A549 and H1299 cells, respectively. [For A549 cells: The clone formation count, migration count, invasion count, and 48-h migration distance ratio were (233.70±18.50), (808.70±6.11), (489.70±53.00), and 1.00±0.03, respectively, in the si-NC group; and (131.30±22.50), (403.00±9.54), (372.70±26.27), and 2.14±0.09, respectively, in the si-SRF group. For H1299 cells: The clone formation count, migration count, invasion count, and 48-h migration distance ratio were (194.30±20.98), (988.70±64.52), (907.70±67.02), and 1.00±0.05, respectively, in the si-NC group; and (137.70±7.77), (665.70±157.10), (565.70±67.01), and 1.52±0.03, respectively, in the si-SRF group. All comparisons showed statistically significant differences (P＜0.05)] JASPAR database prediction shows that SRF and lncRNA FGD5-AS1 have binding site. The double luciferase experiment, CHIP and EMSA experiments showed that SRF could regulate lncRNA FGD5-AS1. In situ hybridization showed that the mean optical density of lncRNA FGD5-AS1 in tissue microarray of LUAD patients (1.28±0.31) was higher than that in adjacent tissues (1.00±0.00, P＜0.001). The results of qRT-PCR experiment showed that the expression level of lncRNA FGD5-AS1 in wax tissues of LUAD patients was higher than that in normal tissues adjacent to cancer (P=0.017). The expression level of lncRNA FGD5-AS1 in plasma of LUAD patients (3.48±2.62) was higher than that of healthy people (1.02±0.03, P＜0.001). CCK-8, cloning, EDU, scratch and Transwell experiments showed that overexpression of lncRNA FGD5-AS1 could promote cell proliferation [For A549 cells: The clone formation count, EdU-positive cell count, invasion count, and 48-h migration distance ratio were (22.67±5.86), (1.00±0.09), (135.70±13.20), and 0.35±0.02, respectively, in the pcDNA3.1 group; and (46.33±9.07), (1.65±0.10), (205.00±13.23), and 0.20±0.01, respectively, in the FGD5-AS1-overexpressing group. All comparisons showed statistically significant differences (P＜0.05)], migration and invasion and vice versa [For H1975 cells: The clone formation count, EdU-positive cell count, invasion count, and 48-h migration distance ratio were (75.33±4.16), (1.00±0.02), (258.70±45.79), and 0.18±0.01, respectively, in the NC group; and (37.00±4.00), (0.52±0.07), (130.70±9.07), and 0.53±0.04, respectively, in the lncRNA FGD5-AS1 knockdown group (si-lncRNA FGD5-AS1 group). All comparisons showed statistically significant differences (P＜0.05)]. Overexpression of lncRNA FGD5-AS1 could rescue the effect of knockdown SRF on the proliferation, migration and invasion of A549 and H1299 cells. The results of subcutaneous tumorigenesis experiment in nude mice indicated that the tumorigenicity of LUAD cells stably knockdown SRF was weakened and vice versa. Conclusion: SRF can promote the progress of LUAD by regulating lncRNA FGD5-AS1.