Oncostatin M (OM) inhibits proliferation of H3922, a human breast cancer cell line derived from a ductal infiltrating carcinoma. We have found that treatment of H3922 cells with OM for 72 h lowers the steadystate level of c-myc mRNA to 16% of that seen in control cells. Our present study showed that down-regulation of c-myc mRNA levels was both dose and time dependent. Results from nuclear run-off analysis and mRNA stability studies established that a major component of the observed OM-induced down-regulation of c-myc mRNA occurs at the transcriptional level. OM treatment of H3922 cells reduced the abundance of actively transcribed c-myc mRNAs to approximately 25% of that observed in control cells. These data were supported by our finding that OM did not significantly affect the half-life of c-myc mRNA in actinomycin-treated H3922 cells. Taken together, these data demonstrate that the suppressive effect of OM on c-myc gene expression in H3922 cells occurs at the transcriptional level.


Supported by the Mountain States Medical Research Institute, Boise, ID and by Grant AIBS 182 from the United States Army Medical Research and Development Command.

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