Endocrine Abstracts

Introduction: Pro-opiomelanocortin (POMC) is a precursor polypeptide which is cleaved to make adrenocorticotrophic hormone (ACTH) in the anterior pituitary. It is activated in Cushing’s disease. Current therapies for Cushing’s disease are inadequate. RNA interference (RNAi) allows highly specific and effective suppression of gene expression by use of short interfering RNAs (siRNAs).

Method: In the current study we employed custom designed siRNAs to silence POMC gene expression in cultured murine pituitary corticotroph tumour cells (AtT20 D16:16). The cells were transfected once with 3 separate custom designed siRNAs, with homology to the exonic region of POMC in both mouse and human sequences. After incubation for 24, 48 and 96 hours the cells and media were harvested. RT-QPCR was used to measure relative POMC mRNA suppression, and ACTH analysed by ELISA.

Results: Transfection efficiency was >80% on both FACS analysis and microscopy. POMC mRNA was reduced by 90% at 24 hours, and 70% at 48 hours and maintained. One siRNA had a greater effect than the other two. ACTH levels were reduced by 56% at 24 hours after a single treatment.

Conclusion: Here RNAi allows long lasting and reproducible suppression of POMC and ACTH in murine corticotroph cells. This may allow gene silencing as a therapeutic in vivo.

This work is supported by a Clinical Training Fellowship for the Society for Endocrinology and Clinical Endocrinology Trust.