Pretranslational regulation of ectopic hCGα production in ChaGo lung cancer cells by sodium butyrate

Abstract

Ectopic production of hCG and its free α subunit by ChaGo lung cancer cells is stimulated by sodium butyrate. To investigate pretranslational regulation in this system, we examined the response of the hCGα and β subunit mRNAs in ChaGo-Kl cells, a clone that produces free hCGα but no hCG or hCGβ in the basal state. When a Northern blot of total RNA from ChaGo cells was hybridized to a [ 32P]- labeled hCGα cDNA probe, a single band was detected that was identical in size (∼ 850 bases) to placental hCGα mRNA. RNA from butyrate-stimulated (5 mM, 24 h) ChaGo cells contained 7.7 times as much hCGα mRNA as RNA from control ChaGo cells. This increase appeared to be relatively selective since no difference in total polyA-containing mRNA levels was detected between butyrate-treated and control cells by [ 32P]oligo(dT) hybridization. In addition, no hCGβ mRNA was detected when Northern and dot blots were hybridized to an hCGβ cDNA probe. In a time course experiment, hCGα mRNA accumulation in butyrate-treated cells increased significantly by 8 h with a maximum increase of 6.1-fold at 24 h compared to control values. Major differences in immunoactive hCGα accumulation were not apparent, however, until after 24 h. These studies show that stimulation of ChaGo hCGα production by butyrate can be completely accounted for by pretranslational events and that failure to detect hCG or free hCGβ production by these cells is not due to poorly translatable RNA or post-translational protein degradation. Thus, exclusive ectopic production of only one of the hCG subunits is likely to be due to selective genomic expression.