SW13 Cells Can Transition between Two Distinct Subtypes by Switching Expression of BRG1 andBrm Genes at the Post-transcriptional Level

Mitsue Yamamichi-Nishina,Taiji Ito,Taketoshi Mizutani,Nobutake Yamamichi,Hirotaka Watanabe,Hideo Iba

doi:10.1074/jbc.m208458200

Mitsue Yamamichi-Nishina, Taiji Ito + Show 4 more

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https://doi.org/10.1074/jbc.m208458200

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Abstract

The human adrenal carcinoma cell line, SW13, has been reported to be deficient in both BRG1 and Brm expression and therefore is considered to lack a functional SWI/SNF complex. We found that the original cell line of SW13 is composed of two subtypes, one that expresses neither BRG1 nor Brm (SW13(vim-)) and the another, which does express both (SW13(vim+)). The presence of BRG1 and Brm in SW13 correlates completely with the cellular ability to express such genes as vimentin, collagenase, c-met, and CD44 that were under the control of a transcription factor, AP-1, which was shown previously to require a functional SWI/SNF complex for its transactivating activity. Transient treatment with inhibitors of histone deacetylase induced a stable transition of SW13(vim-) to a cell type indistinguishable from SW13(vim+), suggesting that these two subtypes are epigenetically different. Run-on analysis indicated that, unlike these four genes driven by AP-1, transcription of the BRG1 and Brm genes in SW13(vim-) are initiated at a frequency comparable with SW13(vim+). In both SW13(vim-) and SW13(vim+) cells, the BRG1 and Brm genes were transcribed through the entire gene at a similar efficiency, indicating that their expression was completely suppressed at the post-transcriptional level in SW13(vim-) cells. We would like to propose that SW13 can spontaneously transition between two subtypes by switching expression of BRG1 and Brm at the post-transcriptional level.

Highlights

Introduction of a Physiological Level ofExogenous BRG1 or Brm in SW13(vimϪ) Switches Expression of vimentin, collagenase, c-met, and CD44 Genes— we used retrovirus vectors to examine whether SW13(vimϪ) can induce vimentin, collagenase, c-met, and CD44 by exogenous expression of BRG1 or Brm at a physiological level
The expression levels of vimentin were determined both by semiquantitative RT-PCR of total RNA (Fig. 1A) and by Western blot analysis of the total cellular lysates (Fig. 1B) and were compared with those of a control cell line, MDA-MB435, that express vimentin. vimentin mRNA and vimentin protein were clearly detectable in SW13(vimϩ) #21 and #22, whereas they are completely undetectable in SW13(vimϪ) #1 and #2
We have reported previously that transactivating activity of AP-1 depends on the presence of a functional SWI/SNF complex and that AP-1 function in SW13 cells was strongly attenuated, because the cells are deficient in the expression of both catalytic subunits of the SWI/SNF complex

Summary

The abbreviations used are

Pc-G, Polycomb group; trx-G, trithorax group; CHAP, cyclic hydroxamic acid-containing peptide; TSA, trichostatin A; 5-azadC, 5-azadeoxycytidine; TPA, 12-O-tetradecanoylphortrithorax group (trx-G) (1–3). Brm and BRG1 have DNA-dependent ATPase activity and are the catalytic subunits of the mammalian SWI/ SNF chromatin remodeling complex. This complex contains either Brm or BRG1, but not both (4), and recent reports on the glucocorticoid receptor (5), c-Myc (6), C/EBP␤ (7), estrogen receptor (8), AP-1 (9), and p53 (10) support a model in which transcription factors recruit the SWI/SNF complex to target genes (11, 12), providing mechanistic links between epigenetic transcriptional regulation and chromatin remodeling (13). Transactivation by the c-Fos/cJun heterodimer (having the highest affinity to BAF60a) was enhanced by cotransfecting Brm or BRG1 into SW13 to recover the functional SWI/SNF complex (9). Phenomenon was related to the deficiency in BRG1 and Brm expression in this cell line

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RESULTS

DISCUSSION