Lycorine affects tamoxifen resistance of breast cancer via m⁶A-based HAGLR

Background: N6-methyladenosine (m⁶A)-mediated epitranscriptomic pathway has been shown to contribute to chemoresistance and radioresistance. Our previous work confirmed the defense of lycorine against tamoxifen resistance of breast cancer (BC) through targeting HOXD antisense growth-associated long non-coding RNA (HAGLR). Whereas, the precise regulation among them remains to be elucidated. The aim of this study was to investigate the role of IGF2BP2-mediated m⁶A methylation in the regulation of HAGLR and its impact on lycorine's effect on tamoxifen resistance in BC.

Methods: m⁶A status was detected via methylated RNA immunoprecipitation-quantitative polymerase chain reaction (MeRIP-qPCR). Relative expression of HAGLR and IGF2BP2 were tested by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot analysis, respectively. Cell viability, proliferation and apoptosis were estimated via Cell Counting Kit-8 (CCK-8), colony formation and flow cytometer analysis. Interplay among IGF2BP2 and HAGLR was tested by RNA immunoprecipitation (RIP) assay. IC₅₀ value of BC cells to tamoxifen was determined by 2,5-diphenyl-2H-tetrazolium bromide (MTT) assay.

Results: Total m⁶A level in tamoxifen-resistant BC cells (TAMR/MCF-7 and TAMR/T47D) was elevated relative to corresponding parental cells and normal mammary epithelial cell line, MCF10A, either with the presence of m⁶A modifications within HAGLR sequence. Moreover, IGF2BP2-mediated m⁶A methylation drove the upregulation and stability of HAGLR in TAMR BC cells. IGF2BP2 served as a key downstream target mediating the anti-tumors of lycorine on TAMR BC. Knockdown of IGF2BP2 or HAGLR could reduce the IC₅₀ value of TAMR/MCF-7 and TAMR/T47D cells to tamoxifen.

Conclusions: Our results demonstrated that lycorine inhibits tamoxifen-resistant BC by repressing IGF2BP2-mediated m⁶A methylation of HAGLR.