A novel member of the SAF (scaffold attachment factor)-box protein family inhibits gene expression and induces apoptosis.
The SLTM [SAF (scaffold attachment factor)-like transcription modulator] protein contains a SAF-box DNA-binding motif and an RNA-binding domain, and shares an overall identity of 34% with SAFB1 {scaffold attachment factor-B1; also known as SAF-B (scaffold attachment factor B), HET [heat-shock protein 27 ERE (oestrogen response element) and TATA-box-binding protein] or HAP (heterogeneous nuclear ribonucleoprotein A1-interacting protein)}. Here, we show that SLTM is localized to the cell nucleus, but excluded from nucleoli, and to a large extent it co-localizes with SAFB1. In the nucleus, SLTM has a punctate distribution and it does not co-localize with SR (serine/arginine) proteins. Overexpression of SAFB1 has been shown to exert a number of inhibitory effects, including suppression of oestrogen signalling. Although SLTM also suppressed the ability of oestrogen to activate a reporter gene in MCF-7 breast-cancer cells, inhibition of a constitutively active beta-galactosidase gene suggested that this was primarily the consequence of a generalized inhibitory effect on transcription. Measurement of RNA synthesis, which showed a particularly marked inhibition of [(3)H]uridine incorporation into mRNA, supported this conclusion. In addition, analysis of cell-cycle parameters, chromatin condensation and cytochrome c release showed that SLTM induced apoptosis in a range of cultured cell lines. Thus the inhibitory effects of SLTM on gene expression appear to result from generalized down-regulation of mRNA synthesis and initiation of apoptosis consequent upon overexpressing the protein. While indicating a crucial role for SLTM in cellular function, these results also emphasize the need for caution when interpreting phenotypic changes associated with manipulation of protein expression levels.
Chan
Ching Wan
CW
Henry Wellcome Laboratories for Integrative Neurosciences and Endocrinology, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK.
Lee
Youn-Bok
YB
Uney
James
J
Flynn
Andrea
A
Tobias
Jonathan H
JH
Norman
Michael
M
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics / Q000502:physiology*; D004965:Estrogen Antagonists / Q000737:chemistry; D004967:Estrogens / Q000378:metabolism / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D036961:Matrix Attachment Region Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D051379:Mice; D005810:Multigene Family / Q000235:genetics / Q000502:physiology*; D034521:Nuclear Matrix-Associated Proteins / Q000235:genetics / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; D004965:Estrogen Antagonists; D004967:Estrogens; D036961:Matrix Attachment Region Binding Proteins; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C523919:SLTM protein, mouse; C500609:scaffold attachment factor B1, mouse