Abstract
Inherent sex differences in various parameters of growth, musculoskeletal function, metabolism, and cytochrome P450 (P450)-dependent drug metabolism have been reported in rats and humans administered typical intermittent/episodic growth hormone (GH) replacement therapy. Having infused and monitored the identical physiologic masculine (episodic) growth hormone profile to both hypophysectomized male and female rats, we observed that induction levels of hepatic CYP2C11 were 35 to 40% lower in females. Associated with the reduced expression of the P450 isoform in the episodic GH-treated females were dramatically lower activation levels of Janus kinase (Jak2), signal transducers and activators of transcription (Stat5A and 5B) as well as 50% less binding of Stat5B to the CYP2C11 promoter. Because the Jak2/Stat5B signaling pathway mediates the effects of the masculine GH profile on its target cells, we conclude that the lower induction level of CYP2C11 in females exposed to the masculine GH profile is probably due, at least in part, to the suboptimum activation of the Jak2/Stat5B pathway. In addition to the reduced activation of the Jak2/Stat5B pathway, we observed lower activational levels of mitogen-activated protein kinase (p44/p42) and, indirectly, nuclear factor-κB in the episodic GH-treated females that may be involved in attenuating the activity of the Jak2/Stat5B pathway diminishing CYP2C11 expression levels.
Footnotes
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↵1 Because this is an in vivo study, and MAPK is known to mediate the activities of numerous factors in addition to GH, it is possible that the elevated nuclear phospho-Erk1 and phospho-Erk2 baselines in male liver were due to some normally occurring, but confounding, male-specific “signal” other than GH.
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This work was supported in part by National Institute of Health Grant GM45758.
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R.N.D. and C.T. contributed equally to the study.
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doi:10.1124/dmd.107.017475.
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ABBREVIATIONS: GH, growth hormone; P450, cytochrome P450; HYPOX, hypophysectomized; Jak, Janus kinase; Stat, signal transducer and activator of transcription; MAPK, mitogen-activated protein kinase; NF-κB, nuclear factor-κB; IκB, inhibitory κB; rGH, rat growth hormone; PCR, polymerase chain reaction; ChIP, chromatin immunoprecipitation assay; Erk, extracellular signal-regulated kinase.
- Received June 28, 2007.
- Accepted August 1, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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