Inhibition of proopiomelanocortin expression by an oligodeoxynucleotide complementary to β-endorphin mRNA

Gene expression in mammalian cells can be suppressed by oligonucleotides complementary to the target mRNA. This strategy was explored as a means of arresting translation of the prohormone precursor proopiomelanocortin (POMC), used as a model system of peptide messengers that are synthesized and released from endocrine and neuronal cells. The synthesis of the POMC- derived peptides adrenocorticotropin (ACTH) and β-endorphin (β-END) was markedly reduced by an oligodeoxynucleotide (ODN) complementary to a region of β-END mRNA in AtT-20 cells, which retain many of the differentiated phenotypes of corticotrophs; this treatment did not affect the steady-state levels of POMC mRNA. Antisense ODN was stable in cell culture medium for 24 h, and cellular uptake was low (≃2.5% of the added ODN); however, the intracellular levels of the ODN were sufficient to form a ribonuclease- resistant duplex with complementary cellular mRNA. Addition of ODN to the cell culture did not affect the cellular levels of chromogranin A-(264- 314)/pancreastatin or cell viability and proliferation, as evidenced by bromodeoxyuridine incorporation and ornithine decarboxylase activity. Microinfusion of the antisense ODN in the rat hypothalamic arcuate nucleus, where the majority of POMC-positive brain perikarya are located, significantly reduced ACTH- and β-END-immunopositive neurons and antisense ODN-treated rats showed substantially less of the grooming behavior usually observed in a novel environment.