Vitamin D receptor is associated with farnesyl diphosphate synthase protein stability and malignant phenotypes in esophageal squamous cell carcinoma cells.

Abstract

Esophageal squamous cell carcinoma (ESCC) is a common digestive malignancy with a poor prognosis, while its underlying molecular mechanisms remain incompletely understood. The vitamin D receptor (VDR) has been implicated in ESCC progression and metabolic regulation; however, its downstream signaling mechanisms remain unclear. This study aimed to investigate whether farnesyl diphosphate synthase (FDPS), a key enzyme in the mevalonate and cholesterol biosynthesis pathway, is involved in VDR-associated ESCC progression. ESCC cell lines were used to examine the biological and molecular effects of VDR. Cell proliferation was assessed after calcitriol treatment, whereas proliferation and migration were assessed after VDR knockdown or overexpression using Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), colony formation, wound-healing, and Transwell assays. A previously published tandem mass tag (TMT)-based proteomic dataset was reanalyzed to identify VDR-associated proteins, followed by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and Western blot validation. FDPS degradation and protein stability were evaluated using proteasome inhibitor MG132, cycloheximide (CHX) chase assays, and ubiquitination immunoprecipitation assays. FDPS knockdown or pharmacological inhibition was applied to determine whether FDPS mediated the effects of VDR. RNA sequencing (RNA-seq) was used to further explore VDR-regulated transcriptomic changes. Calcitriol inhibited ESCC cell proliferation. VDR knockdown suppressed ESCC cell proliferation and migration, whereas VDR overexpression promoted these malignant phenotypes, indicating a potential context-dependent pro-tumor association in the tested ESCC cells. Reanalysis of published TMT-based proteomic data identified several VDR-regulated proteins involved in metabolism, including FDPS, as a candidate downstream effector. Validation experiments showed that VDR manipulation was associated with changes in FDPS primarily at the protein level rather than at the mRNA level. In mechanistic assays, VDR overexpression was associated with increased FDPS protein abundance and reduced FDPS ubiquitination, suggesting that VDR expression may maintain FDPS abundance by altering ubiquitin-proteasome-mediated degradation. FDPS knockdown or inhibition attenuated VDR-induced ESCC cell proliferation and migration, supporting FDPS as a functional contributor to the VDR-associated phenotype. RNA-seq analysis suggested that VDR affected multiple oncogenic and metabolic pathways. In the tested in vitro models, higher VDR expression was associated with increased ESCC cell proliferation and migration, greater FDPS protein abundance, and lower FDPS ubiquitination. The VDR-FDPS association may represent a potential metabolic vulnerability in ESCC.

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