AI Article Synopsis
- Hemopexin (HPX) transports heme to liver cells, where it triggers a significant increase in heme oxygenase (HO) mRNA levels, peaking at 20-25 times higher within 3 hours at a 10 µM concentration.
- The rise in HO mRNA results from enhanced transcription of the HO gene, confirmed by nuclear run-on assays.
- Additionally, heme-HPX transport into Hepa cells also leads to a substantial decrease in transferrin receptor (TfR) mRNA levels, although this drop is not due to changes in TfR gene transcription, and similar effects are seen in HL-60 human cells.
Article Abstract
Hemopexin (HPX) transports heme to liver parenchymal cells, undergoes receptor-mediated endocytosis, and recycles intact. Incubation of mouse hepatoma (Hepa) cells with heme-HPX causes a rapid dose- and time-dependent increase in the steady-state level of heme oxygenase (HO) mRNA. A maximum induction of 20-25-fold is achieved within 3 h after incubation with 10 microM heme-HPX. This accumulation of HO mRNA results primarily from increased transcription of the HO gene as judged by in vitro nuclear run-on assays. In addition, receptor-mediated transport of heme into Hepa cells significantly decreases the steady-state level of transferrin receptor (TfR) mRNA. While a 25-30-fold decrease in the amount of TfR mRNA is observed within 3 h of incubation of Hepa cells with 10 microM heme-HPX, no significant change in the rate of TfR gene transcription was detected. These regulatory effects of heme-HPX are not restricted to hepatic cells but are also observed in human promyelocytic HL-60 cells. This is the first direct demonstration of receptor-mediated transport of heme by hemopexin regulating gene expression in mammalian cells.
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