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Heterogeneous SWI/SNF chromatin remodeling complexes promote expression of microphthalmia-associated transcription factor target genes in melanoma.

Keenen B, Qi H, Saladi SV, Yeung M, de la Serna IL - Oncogene (2009)

Bottom Line: The microphthalmia-associated transcription factor (MITF) promotes melanocyte differentiation and cell-cycle arrest.SWI/SNF chromatin remodeling enzymes are multiprotein complexes composed of one of two related ATPases, BRG1 or BRM, and 9-12-associated factors (BAFs).Downregulation of the single ATPase, BRM, in SK-MEL5 cells inhibited expression of both differentiation-specific and pro-proliferative MITF target genes and inhibited tumorigenicity in vitro.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Cancer Biology, University of Toledo College of Medicine, Toledo, OH 43614, USA.

ABSTRACT
The microphthalmia-associated transcription factor (MITF) promotes melanocyte differentiation and cell-cycle arrest. Paradoxically, MITF also promotes melanoma survival and proliferation, acting like a lineage survival oncogene. Thus, it is critically important to understand the mechanisms that regulate MITF activity in melanoma cells. SWI/SNF chromatin remodeling enzymes are multiprotein complexes composed of one of two related ATPases, BRG1 or BRM, and 9-12-associated factors (BAFs). We previously determined that BRG1 interacts with MITF to promote melanocyte differentiation. However, it was unclear whether SWI/SNF enzymes regulate the expression of different classes of MITF target genes in melanoma. In this study, we characterized SWI/SNF subunit expression in melanoma cells and observed downregulation of BRG1 or BRM, but not concomitant loss of both ATPases. Re-introduction of BRG1 in BRG1-deficient SK-MEL5 cells enhanced expression of differentiation-specific MITF target genes and resistance to cisplatin. Downregulation of the single ATPase, BRM, in SK-MEL5 cells inhibited expression of both differentiation-specific and pro-proliferative MITF target genes and inhibited tumorigenicity in vitro. Our data suggest that heterogeneous SWI/SNF complexes composed of either the BRG1 or BRM subunit promote expression of distinct and overlapping MITF target genes and that at least one ATPase is required for melanoma tumorigenicity.

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A. Detection by Western blotting of SWI/SNF subunit expression in melanocytes from two different donors, eight human melanoma cell lines, SW13, and HeLa cells. Tubulin is a loading control. B. Detection of BRG1 and BRM mRNA levels by real time RT-PCR. mRNA levels were standardized to 18S rRNA and expressed as values relative to those in human melanocytes.
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Figure 1: A. Detection by Western blotting of SWI/SNF subunit expression in melanocytes from two different donors, eight human melanoma cell lines, SW13, and HeLa cells. Tubulin is a loading control. B. Detection of BRG1 and BRM mRNA levels by real time RT-PCR. mRNA levels were standardized to 18S rRNA and expressed as values relative to those in human melanocytes.

Mentions: We characterized the expression of BRG1 and BRM and the expression of other SWI/SNF proteins in normal human melanocytes and established human melanoma cell lines. We found that melanocytes expressed high levels of both BRG1 and BRM when compared to HeLa cells (known to express high levels of many SWI/SNF components) and SW13 cells (known to be deficient in both BRG1 and BRM) but that BRG1 and BRM expression was variable in a number of melanoma cell lines (Fig. 1A). SK-MEL5 cells, isolated from an axillary node metastasis (Pollack et al., 1981), did not express BRG1 but had levels of BRM comparable to melanocytes. PMWK, derived from a primary melanoma (Vink et al., 1993), and YUMAC, derived from metastatic melanoma (Hoek et al., 2004), had virtually undetectable levels of BRM but expressed high levels of BRG1 (Fig. 1A). All the melanoma cells expressed high levels of several other SWI/SNF components, including the core subunits, INI1 and BAF155. Therefore, if the expressed SWI/SNF components are functional, then overall SWI/SNF activity in a subset of melanoma cells may be compromised by down-regulation of one SWI/SNF ATPase but not completely eliminated because the alternative ATPase is retained and the other core SWI/SNF components are also highly expressed.


Heterogeneous SWI/SNF chromatin remodeling complexes promote expression of microphthalmia-associated transcription factor target genes in melanoma.

Keenen B, Qi H, Saladi SV, Yeung M, de la Serna IL - Oncogene (2009)

A. Detection by Western blotting of SWI/SNF subunit expression in melanocytes from two different donors, eight human melanoma cell lines, SW13, and HeLa cells. Tubulin is a loading control. B. Detection of BRG1 and BRM mRNA levels by real time RT-PCR. mRNA levels were standardized to 18S rRNA and expressed as values relative to those in human melanocytes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2803337&req=5

Figure 1: A. Detection by Western blotting of SWI/SNF subunit expression in melanocytes from two different donors, eight human melanoma cell lines, SW13, and HeLa cells. Tubulin is a loading control. B. Detection of BRG1 and BRM mRNA levels by real time RT-PCR. mRNA levels were standardized to 18S rRNA and expressed as values relative to those in human melanocytes.
Mentions: We characterized the expression of BRG1 and BRM and the expression of other SWI/SNF proteins in normal human melanocytes and established human melanoma cell lines. We found that melanocytes expressed high levels of both BRG1 and BRM when compared to HeLa cells (known to express high levels of many SWI/SNF components) and SW13 cells (known to be deficient in both BRG1 and BRM) but that BRG1 and BRM expression was variable in a number of melanoma cell lines (Fig. 1A). SK-MEL5 cells, isolated from an axillary node metastasis (Pollack et al., 1981), did not express BRG1 but had levels of BRM comparable to melanocytes. PMWK, derived from a primary melanoma (Vink et al., 1993), and YUMAC, derived from metastatic melanoma (Hoek et al., 2004), had virtually undetectable levels of BRM but expressed high levels of BRG1 (Fig. 1A). All the melanoma cells expressed high levels of several other SWI/SNF components, including the core subunits, INI1 and BAF155. Therefore, if the expressed SWI/SNF components are functional, then overall SWI/SNF activity in a subset of melanoma cells may be compromised by down-regulation of one SWI/SNF ATPase but not completely eliminated because the alternative ATPase is retained and the other core SWI/SNF components are also highly expressed.

Bottom Line: The microphthalmia-associated transcription factor (MITF) promotes melanocyte differentiation and cell-cycle arrest.SWI/SNF chromatin remodeling enzymes are multiprotein complexes composed of one of two related ATPases, BRG1 or BRM, and 9-12-associated factors (BAFs).Downregulation of the single ATPase, BRM, in SK-MEL5 cells inhibited expression of both differentiation-specific and pro-proliferative MITF target genes and inhibited tumorigenicity in vitro.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Cancer Biology, University of Toledo College of Medicine, Toledo, OH 43614, USA.

ABSTRACT
The microphthalmia-associated transcription factor (MITF) promotes melanocyte differentiation and cell-cycle arrest. Paradoxically, MITF also promotes melanoma survival and proliferation, acting like a lineage survival oncogene. Thus, it is critically important to understand the mechanisms that regulate MITF activity in melanoma cells. SWI/SNF chromatin remodeling enzymes are multiprotein complexes composed of one of two related ATPases, BRG1 or BRM, and 9-12-associated factors (BAFs). We previously determined that BRG1 interacts with MITF to promote melanocyte differentiation. However, it was unclear whether SWI/SNF enzymes regulate the expression of different classes of MITF target genes in melanoma. In this study, we characterized SWI/SNF subunit expression in melanoma cells and observed downregulation of BRG1 or BRM, but not concomitant loss of both ATPases. Re-introduction of BRG1 in BRG1-deficient SK-MEL5 cells enhanced expression of differentiation-specific MITF target genes and resistance to cisplatin. Downregulation of the single ATPase, BRM, in SK-MEL5 cells inhibited expression of both differentiation-specific and pro-proliferative MITF target genes and inhibited tumorigenicity in vitro. Our data suggest that heterogeneous SWI/SNF complexes composed of either the BRG1 or BRM subunit promote expression of distinct and overlapping MITF target genes and that at least one ATPase is required for melanoma tumorigenicity.

Show MeSH
Related in: MedlinePlus