Supporting data for "The functional roles and therapeutic implication of small extracellular vesicle- and cytosolic MED8 in tumorigenesis and progression"

<p dir="ltr">MED8, a Mediator complex subunit, was validated to drive tumor progression through extracellular vesicle-mediated communication and intracellular metabolic reprogramming. It was identified that MED8 is a selectively enriched cargo in small extracellular vesicles (sEV) derived from metastatic hepatocellular carcinoma (HCC) cells. Functional studies revealed that sEV-associated MED8 induces oxidative stress, DNA damage, and PI3K/Akt activation in recipient cells, promoting tumor-like transformation and metastasis in vivo. Complementing its sEV functions, intracellular MED8 transcriptionally upregulates ELOVL1, enhancing synthesis of C24 acyl-CoA and subsequent C24 ceramide (Cer) production. This Cer is metabolized through two divergent pathways: conversion to C24 sphingomyelin (SM) to enhance membrane fluidity and cell motility, and phosphorylation by sphingosine kinases (SphKs) to generate sphingosine-1-phosphate (S1P), which activates pro-survival signaling and boosts mitochondrial respiration. Mechanistically, MED8 interacts with HSF1 to transcriptionally activate ELOVL1 while simultaneously promoting SphK phosphorylation. Genetic and pharmacological inhibition studies confirmed that both ELOVL1-mediated C24 Cer synthesis and SphK-mediated S1P production are essential for MED8-driven tumor progression. Clinical analyses revealed MED8 overexpression correlates with poor prognosis across multiple cancers. Collectively, these findings establish MED8 as a master regulator of tumor progression that bridges sEV-mediated microenvironment remodeling and intracellular lipid metabolic rewiring, suggesting therapeutic targeting of the MED8-ELOVL1-SphK axis may combat advanced malignancies.</p>