Epigenetic silencing of the endothelin-B receptor gene in non-small cell lung cancer

Endothelin-1 is overexpressed in several tumor types. Activation of the endothelin-A (ET(A)) receptor may promote cell growth, angiogenesis and invasion, and inhibits the apoptotic process, while activation of the endothelin-B (ET(B)) receptor may induce cell death by apoptosis and inhibit tumor progression. Hypermethylation and subsequent silencing of the ET(B) receptor gene promoter has been reported in some cancer types. As the endothelin pathway is Subject to research for pharmacological cancer treatment, we investigated the extent of epigenetic deregulation of the ET(B) receptor gene in non-small cell lung cancer (NSCLC). We scanned 64 NSCLC paired tumor/normal surgical specimens for the ET(B) receptor promoter for methylation by developing four pyrosequencing assays that covered 24 CpGs. The ET(B) receptor promoter was significantly hypermethylated in 31 (48%) of tumor samples, presenting considerably higher methylation in 22/24 CpG sites compared with the normal counterpart tissues. ET(B) receptor mRNA levels were reduced in all lung tumors compared with normal adjacent lung tissue, indicating the potentially important involvement of this gene in lung cancer development. Furthermore, tumor samples with ET(B) receptor gene methylation tended to have lower receptor mRNA levels compared with unmethylated tumor specimens, suggesting a primary epigenetic role in ET(B) receptor silencing. Our results point to a significant involvement of ET(B) receptor epigenetic deregulation in the pathogenesis of lung cancer making the gene a promising candidate biomarker for response to regimens modulating the endothelin axis.