Immunodetection of nmt55/p54nrb isoforms in human breast cancer.
BACKGROUND
We previously identified and characterized a novel 55 kDa nuclear protein, termed nmt55/p54nrb, whose expression was decreased in a subset of human breast tumors. The objective of this study was to determine if this reduced expression in human breast tumors was attributed to the regulation of mRNA transcription or the presence of altered forms of this protein.


RESULTS
Northern blot analysis and ribonuclease protection assay indicated that nmt55/p54nrb mRNA is expressed at varying levels in estrogen receptor positive (ER+) and estrogen receptor negative (ER-) human breast tumors suggesting that reduced expression of nmt55/p54nrb protein in ER- tumors was not due to transcriptional regulation. To determine if multiple protein isoforms are expressed in breast cancer, we utilized Western blot and immunohistochemical analyses, which revealed the expression of an nmt55/p54nrb protein isoform in a subset of ER+ tumors. This subset of ER+ human breast tumors expressed an altered form of nmt55/p54nrb that was undetectable with an amino-terminal specific antibody suggesting that this isoform contains alterations or modifications within the amino terminal domain.


CONCLUSIONS
Our study indicates that nmt55/p54nrb protein is post-transcriptionally regulated in human breast tumors leading to reduced expression in ER- tumors and the expression of an amino terminal altered isoform in a subset of ER+ tumors. The potential involvement of nmt55/p54nrb in RNA binding and pre-mRNA splicing may be important for normal cell growth and function; thus, loss or alteration of protein structure may contribute to tumor growth and progression.
Pavao
M
M
Department of Biochemistry, Boston University School of Medicine, Center for Advanced Biomedical Research, 700 Albany Street, W607, Boston, MA 02118, USA. mpavao@bu.edu
Huang
Y H
YH
Hafer
L J
LJ
Moreland
R B
RB
Traish
A M
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D000230:Adenocarcinoma / Q000737:chemistry / Q000473:pathology; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000737:chemistry* / Q000473:pathology; D002457:Cell Extracts / Q000032:analysis / Q000276:immunology; D004268:DNA-Binding Proteins; D006801:Humans; D007150:Immunohistochemistry; D015530:Nuclear Matrix / Q000737:chemistry*; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins / Q000032:analysis* / Q000276:immunology; D050810:Octamer Transcription Factors; D020033:Protein Isoforms / Q000032:analysis / Q000276:immunology; D011499:Protein Processing, Post-Translational / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D016601:RNA-Binding Proteins / Q000032:analysis* / Q000276:immunology; D011960:Receptors, Estrogen / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D002457:Cell Extracts; D004268:DNA-Binding Proteins; C083214:NONO protein, human; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D050810:Octamer Transcription Factors; D020033:Protein Isoforms; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011960:Receptors, Estrogen