Point mutations within AT-hook domains of the HMGI homologue HMGIYL1 affect binding to gene promoter but not to four-way junction DNA

High-mobility group I/Y (HMGI/Y) proteins are chromosomal proteins involved in gene and chromatin regulation. Elevated levels of HMGI/Y proteins were reported in diverse malignant tumors, and rearrangements of their genes are casually involved in the development of benign tumors. In humans, the chromosomal locus Xp22 has been often found to be affected in diverse benign mesenchymal tumors. Recent studies revealed that this region contains a retropseudogene HMGIYL1 which potentially can be activated in a way of "exonization" upon aberrations involving this region. The coding sequence of the HMGIY-L1 is highly homologous to the HMGI(Y) gene. On the protein level, both HMGIYL1 and HMGI differ at few amino acid residues, including their putative DNA-binding domains (DBDs). Here we have approached the question of whether the HMGIYL1 product would be able to adopt a role of HMGI in the context of binding to gene promoters and chromatin. Comparative binding studies, employing protein footprinting technique, revealed that HMGIYL1 has lost the ability to bind to the promoter of the interferon beta gene, but retained its high affinity for the four-way junction DNA. Our results stress the importance of particular residues within the DBDs for DNA binding and demonstrate that tight binding of HMGI/Y proteins to the four-way junction DNA can be achieved in alternative ways. The binding of HMGIYL1 to four-way junction DNA suggests that activation of the HMGIYL1 gene would yield a protein sharing some binding properties with HMG1-box proteins and histone H1. Thus, the HMGIYL1 could interplay together with these components in chromatin regulation.     

Nuclear matrix localization of high mobility group protein I(Y) in a transgenic mouse model for prostate cancer

Nuclear shape and the underlying nuclear structure, the nuclear matrix in cancer cells. Since the NM composition is considered to maintain nuclear shape and architecture, nuclear matrix proteins (NMPs) may be involved in transformation. Our laboratory has recently characterized a subset of NMPs that are associated with prostate cancer development in the transgenic adenocarcinoma of mouse prostate (TRAMP) model. One of the identified NMPs, E3E, has a similar molecular weight (22 kDa) with a protein known as HMGI(Y). HMGI(Y) belongs to a group of non-histone and chromatin-associated proteins, high-mobility-group (HMG) proteins, and it has been shown to associate with the NM. HMGI(Y) has been reported to be elevated in different types of cancer including prostate cancer. In this study, we examined the expression of HMGI(Y) protein in the NMP composition of the TRAMP model during the progression from normal to neoplasia. The expression of HMGI(Y) in the NMP extracts of three prostatic epithelial cell lines derived from a 32-week TRAMP mouse: TRAMP-C1, TRAMP-C2, and TRAMP-C3 was also examined. Using both one-dimensional and high-resolution two-dimensional immunoblot analyses, we found that: (i) HMGI(Y) is a nuclear matrix protein expressed as two protein bands with MW of 22-24 kDa and (ii) HMGI(Y) expression is correlated with neoplastic and malignant properties in late stage TRAMP prostate tumors. Overall, these findings support the evidence that HMGI(Y) can be utilized as a marker and prognostic tool for prostate cancer.