Research article

Immunodetection of nmt55/p54^nrb isoforms in human breast cancer

Matthew Pavao , Yue-Hua Huang , Laurie J Hafer , Robert B Moreland and Abdulmaged M Traish

Department of Biochemistry, Boston University School of Medicine, Center for Advanced Biomedical Research, 700 Albany Street, W607, Boston, MA 02118, USA

author email corresponding author email

BMC Cancer 2001, 1:15doi:10.1186/1471-2407-1-15

Published:	29 October 2001

Abstract

Background

We previously identified and characterized a novel 55 kDa nuclear protein, termed nmt55/p54^nrb, 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/p54^nrb 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/p54^nrb 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/p54^nrb protein isoform in a subset of ER+ tumors. This subset of ER+ human breast tumors expressed an altered form of nmt55/p54^nrb 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/p54^nrb 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/p54^nrb 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.