Tamoxifen differentially modulates endometrial hyperplasia via wild-type and mutant p53 regulation of the ALKBH5-REG1A axis.

Introduction: Tamoxifen is a cornerstone of endocrine therapy for estrogen receptor-positive breast cancer; however, its partial estrogen agonist activity in the endometrium predisposes patients to hyperplasia and, in some cases, malignant transformation. The molecular mechanisms underlying this tissue-specific adverse effect remain incompletely understood. Methods: We employed immortalized human endometrial epithelial cells to investigate the role of p53 in tamoxifen-induced proliferation. Cells were genetically manipulated to express wild-type (WT) or mutant p53 (R248Q), and ALKBH5 or REG1A was silenced or overexpressed using lentiviral constructs. A comprehensive set of molecular techniques-including quantitative reverse transcription PCR (qRT-PCR), Western blotting, chromatin immunoprecipitation (ChIP), luciferase reporter assays, methylated RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP), and functional proliferation assays (CCK-8 and colony formation)-was applied to dissect transcriptional and post-transcriptional regulatory mechanisms. Results: Tamoxifen promoted the recruitment of WT p53 to the ALKBH5 promoter, transcriptionally activating this m Conclusions: Tamoxifen's anti-proliferative effects in endometrial epithelial cells are critically dependent on WT p53, which coordinates a protective epitranscriptomic regulatory axis. In contrast, mutant p53 disrupts this checkpoint and redirects tamoxifen signaling toward hyperproliferation. These findings establish a mechanistic link between hormonal signaling, p53 allelic status, and m