MicroRNA-29b-5p regulates cell proliferation and cancer stemness via TGF-β/p300 pathway in human synovial sarcoma

Synovial sarcoma (SS) is a rare and aggressive soft tissue malignancy characterized by t(X;18)(p11.2;q11.2) translocation, which results in the SYT-SSX fusion gene. SS exhibits cancer stem cell-like properties that contribute to its invasiveness. Recent evidence implicates microRNA-29b (miR-29b) could regulate TGF-β pathway and its downstream gene EP300 may be involved in these traits. Bioinformatics tools (miRDB, TargetScan, and miRanda) were used to predict the interaction between miR-29b-5p and EP300, which was validated via dual-luciferase reporter assays and RNA-binding protein immunoprecipitation. The expression levels of miR-29b-5p and EP300, along with those of cancer stem cell markers, LIF-LIFR signaling, and Ki-67 proliferation indices, were analyzed in SS tissues, parental cells, and spheroid cells. Spheroids derived from SW982 and SSX1 cells cultured in serum-free suspension presented elevated levels of cancer stem cell markers and increased proliferation, migration, and invasion capacities, particularly SYT-SSX1-derived spheroids. Compared with parental cells, spheroids presented reduced miR-29b-5p expression and increased EP300 expression. The overexpression of miR-29b-5p suppressed spheroid formation; stemness marker expression; and cell proliferation, migration, and invasion, whereas its inhibition had the opposite effect. Compared with individual silencing, co-silencing of miR-29b-5p and EP300 further attenuated cancer stem cell-like traits, underscoring their regulatory interplay. In conclusion, miR-29b-5p may suppresses cancer stemness and aggressiveness in SS to some extent by targeting EP300, with a relatively more pronounced effect in SSX1 cells. Preliminarily these fundings suggest that miR-29b-5p-mediated modulation of EP300 and the TGF-β signaling pathway may provide a potential research data for synovial sarcoma studies.