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Title: MEQ IS PREDOMINANTLY LOCALIZED IN THE NUCLEOLI AND BLOCKS TNF-ALPHA-INDUCEDAPOPTOSIS

Author
item LIU, J-L - CASE WESTERN RESERVE
item Lee, Lucy
item KUNG, H-J - CASE WESTERN RESERVE

Submitted to: International Marek's Disease Symposium Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 9/7/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: MEQ encodes a 339 aa bZIP protein that is homologous to jun/fos families of transcription factors. Here we show that MEQ is localized in the nucleus, and interestingly, with a predominant fraction expressed in the nucleolus. This makes MEQ the first bZIP protein to be identified in the nucleoli. MEQ contains two clusters of basic residues, designated as the basic region 1 (BR1) and the basic region 2 (BR2). Using a series of deletion mutants, we have mapped the primary nuclear localization signal (NLS) and the sole nucleolar localization signal (NoLS) to the BR2 region. BR1 only serves an auxiliary function in the nuclear translocation of MEQ. To demonstrate that BR2 is a bona fide NoLS, the BR2 peptide was fused to a cytoplasmic protein and enabled the latter to migrate into the nucleus and nucleolus. Our studies provide evidence that MEQ is both a nucleur and nucleolar protein and add MEQ to the growing list of transactivators which are expressed in the nucleolus. We also report here the transforming properties of MEQ. First, Rat-2 cells infected with MEQ-carrying retrovirus become morphologically transformed, lose contact inhibition, and exhibit the capability of anchorage-independent growth. Secondly, MEQ-transformed Rat-2 cells are resistant to apoptosis induced by either tumor necrosis factor (TNF) or ceramide. The expression of Bcl-2 is up-regulated in cells over-expressing MEQ. Thirdly, upon serum withdrawal, vector-infected Rat-2 cells undergo either growth arrest of apoptosis. In contrast, Meq-transformed Rat-2 cells are able to proliferate continuously. Taken together, our results indicate that MEQ exhibits some of the transforming properties shown for oncoproteins of other tumor viruses.