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Comment |
Regulation of Kruppel-like factor 4, 9 and 13 genes and the steroidogenic genes LDLR, StAR and CYP11A in ovarian granulosa cells. Natesampillai S et al. Kruppel-like factors (KLF's) are important Sp1-like eukaryotic transcriptional proteins. The LDLR, StAR and CYP11A genes exhibit GC-rich Sp1-like sites, which have the potential to bind KLF's in multiprotein complexes. We now report that KLF4, KLF9 and KLF13 transcripts are expressed in and regulate ovarian cells. KLF4 and 13, but not KLF9, mRNA expression was induced and then repressed over time (P < 0.001). Combined LH and IGF-I stimulation increased KLF4 mRNA at 2 h (P < 0.01), whereas LH decreased KLF13 mRNA at 6 h (P < 0.05) and IGF-I reduced KLF13 at 24 h (P < 0.01) compared with untreated control. KLF9 was not regulated by either hormone. Transient transfection of KLF4, KLF9 and KLF13 suppressed LDLR/luc, StAR/luc and CYP11A/luc by 80 to 90% (P < 0.001). Histone-deacetylase (HDAC) inhibitors stimulated LDLR/luc by 5-6 fold and StAR/luc and CYP11A/luc activity by 2-fold (P < 0.001), and partially reversed suppression by all 3 KLF's (P < 0.001). Deletion of the zinc-finger domain of KLF13 abrogated repression of LDLR/luc. Lentiviral overexpression of the KLF13 gene suppressed LDLR mRNA (P < 0.001) and CYP11A mRNA (P = 0.003), but increased StAR mRNA (P = 0.007). Collectively, these data suggest that KLF's may recruit inhibitory complexes containing HDAC corepressors, thereby repressing LDLR and CYP11A transcription. Conversely, KLF13 may recruit unknown coactivators or stabilize StAR mRNA, thereby explaining enhancement of in situ StAR gene expression. These data introduce new potent gonadal transregulators of genes encoding proteins that mediate sterol uptake and steroid biosynthesis. Key words: KLF4, KLF9, KLF13, LDLR, StAR.
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