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2D DIGE sheds light on the metastasis suppressor BRMS1
metastasis, Bravo’s group conducted a yeast two-hybrid screen that identified, among other proteins, a transcription factor that interacts with BRMS1 (unpublished results). This finding led them to question whether BRMS1 affects the transcription of other genes, which might underlie its ability to suppress metastasis. Therefore, the researchers used 2D difference gel electrophoresis (DIGE) coupled with MS to compare the protein expression profiles of wild-type melanoma cells (WT), melanoma cells overexpressing BRMS1 (Mel-BRMS1), and melanoma cells in which endogenous BRMS1 was silenced by a short hairpin RNA (sh635).
tional repression might not be direct but may occur through interactions of Metastasis, or the spreading of canBRMS1 with proteins in the transcripcer cells from a primary tumor to tional machinery.” distant sites, is the leading cause of The differentially expressed proteins cancer-related death. The metastatic identified in the study function mainly cascade involves a complex sequence in cell maintenance, growth regulaof events that begins with the detachtion, signaling, and survival. Several of ment of primary tumor cells from the the identified proteins regulate actin extracellular matrix and ends with the dynamics, suggesting that BRMS1 might vascularization of the metastasized suppress metastasis in part by affecting tumor at its new site. During the past cytoskeletal structures such as focal 10 years, researchers have discovered adhesions or lamellipodia. Unexpecta group of genes known as metastasis edly, the researchers found that some suppressors that can put the brakes on proteins involved in drug and chemometastasizing tumor cells. However, resistance in different tumor types the precise functions of many of these were overexpressed when BRMS1 was genes are enigmatic. In this silenced. This result sugissue of JPR (pp 4006−4018), gests that highly metastatic MALDI TOFMS José Rivera, Diego Megias, cancer cells that lack BRMS1 and Jerónimo Bravo at the expression might be more Centro Nacional de Invesresistant to chemotherapy Mel-BRMS1 tigaciones Oncológicas because of enhanced ex(Spain) describe a propression of these proteins. teomics-based strategy that The 2D DIGE results were WT helps unravel the role of the validated by western blotbreast cancer metastasis ting and functional assays sh635 suppressor 1 (BRMS1). of differentially expressed 2DE WT BRMS1 sh635 Although many genes proteins with known roles in Melanoma DIGE analysis inhibit both tumorigenesis metastasis. cell culture and metastasis, metastaAlthough these results sis suppressor genes are provide tantalizing clues Mystery function. 2D DIGE and MS analyses of proteins from melanoma unique because they specifto the function of BRMS1, cells that express different levels of BRMS1 reveal new clues about the ically block secondary tuBravo emphasizes that function of the metastasis suppressor. mor formation without afthis study is only a starting fecting the primary tumor. point. “We obtained a lot Overexpression of BRMS1 decreases the The comparisons of WT versus Melof information that might be relevant, metastatic potential of human breast BRMS1 and WT versus sh635 extracts but we have lots of work to do,” he says. cancer and melanoma cells, whereas revealed expression differences in 79 “We now have many hypotheses to test. tumor cell lines with low levels of protein spots. These spots were exThis study has opened many lines of BRMS1 are highly metastatic. Although cised from a preparative gel, digested research into BRMS1 function.” Further BRMS1 has been implicated in various with trypsin, and analyzed by MALDI clues to the role of BRMS1 in metastasis processes, including intercellular comTOFMS. A total of 43 unique proteins suppression should be revealed by were identified unambiguously. Inter munication through gap junctions and the protein’s X-ray crystal structure, transcriptional regulation, its precise estingly, ~80% of proteins that were which Bravo’s group is pursuing. In admolecular functions remain mysteridifferentially expressed between dition, the researchers plan to further ous. “Very little is known about either Mel-BRMS1 and WT cells were downinvestigate the importance of BRMS1 in the biochemistry or the interactions regulated in BRMS1-overexpressing cytoskeletal rearrangement and in cheof BRMS1,” Bravo says. “There are no cells, whereas all of the differentially moresistance of cancer cells. The aueasily identifiable motifs in the protein expressed proteins in sh635 cells were thors hope that the 2D DIGE results will sequence, and no proteins similar to up-regulated. According to Bravo, “This help researchers pull away the shroud human BRMS1 have been found in zeresult seems to suggest that transcripof secrecy that currently surrounds the brafish, C. elegans, or yeast.” tional repression might be one of the metastasis suppressor BRMS1. To explore the role of BRMS1 in functions of BRMS1. The transcrip—Laura Cassiday
3874 Journal of Proteome Research • Vol. 6, No. 10, 2007
© 2007 American Chemical Society
