Aljoscha M. Flohr

Molecular characterization of the canine HMGB1

Due to the close similarities of numerous canine diseases to their human counterparts, the dog could join the mouse as the species of choice to unravel the genetic background of complex diseases as e.g. cancer and metabolic diseases. Accordingly, the role of the dog as a model for therapeutic approaches is strongly increasing. However, prerequisite for such studies is the characterization of the corresponding canine genes. Recently, the human high mobility group protein B1 (HMGB1) has attracted considerable interest of oncologists because of what is called its “double life”. Besides its function as an architectural transcription factor HMGB1 can also be secreted by certain cells and then acts as a ligand for the receptor for advanced glycation end products (RAGE). The binding of HMGB1 to RAGE can activate key cell signaling pathways, such as p38MAPK, JNK, and p42/p44MAPK emphasizing the important role of HMGB1 in inflammation and tumor metastasis. These results make HMGB1 a very interesting target for therapeutic studies done in model organisms like the dog. In this study we characterized the molecular structure of the canine HMGB1 gene on genomic and cDNA levels, its predicted protein, the gene locus and a basic expression pattern.

Sequencing of intron 3 of HMGA2 uncovers the existence of a novel exon

Aberrations affecting the gene encoding the high mobility group protein HMGA2 (formerly HMGIC) have been found in a variety of human tumors, e.g., uterine leiomyomas, lipomas, and pulmonary chondroid hamartomas. These aberrations lead to fusion genes, transcriptional up‐regulation, or aberrant transcripts of HMGA2. In the latter case, truncated transcripts consisting of exons 1 to 3 of HMGA2, encoding the three DNA‐binding domains, and ectopic sequences derived from chromosome 12 are frequent. There are several lines of evidence indicating that the biological and tumorigenic features of truncated HMGA2 derivatives, i.e., those composed of the DNA‐binding domains and a shortened acidic tail, clearly differ from those of the normal protein consisting of three DNA‐binding domains and one large acidic tail. By sequencing the complete 112 kb third intron of HMGA2, we were able to detect several of the ectopic sequences, known as fused to HMGA2. Expression studies revealed co‐expression of one of these transcripts with the normal transcript in tumors with 12q14‐15 aberrations as well as in other tumors, and in normal tissues. Thus, this transcript (HMGA2b) is flanked by an alternative terminal exon of HMGA2. Due to the loss of the part encoding the acidic tail, the expression of the latter transcript may have more striking effects than the “wild type” HMGA2 (HMGA2a) in terms of tumorigenesis. This finding clearly indicates that functional studies also should address the role of the HMGA2b transcript.

Expression of the high-mobility group protein HMGI(Y) in human trophoblast: potential role in trophoblast invasion of maternal tissue

The high-mobility group protein HMGI(Y) is a member of a family of non-histone chromosomal proteins, which have been implicated in the regulation of inducible gene transcription, integration of retroviruses into chromosomes and induction of neoplastic transformation and metastatic progression in cancer cells. The human trophoblast is a tissue that shares proliferation capacity and invasiveness with neoplastic tissues, but in which these processes are tightly regulated. In the present study, we analyzed the expression of HMGI(Y) in the human placenta using immunohistochemistry. We found expression of HMGI(Y), with nuclear localization, in the villous cytotrophoblast (vCT), which is a highly proliferative cell type. In contrast, the majority of the nuclei of the villous syncytiotrophoblast, a terminally differentiated tissue, was negative. Interestingly, expression of HMGI(Y) was strongest in anchoring villi at the implantation site and in extravillous (intermediate) trophoblast (EVT) invading the maternal decidua. As vCT cells differentiate to become EVT, the HMGI(Y) protein appears to switch from a nuclear to a cytoplasmic localization. Expression of HMGI(Y) in isolated trophoblast populations in primary cell culture was also confirmed using Western-blot analysis. This study shows for the first time expression and localization of HMGI(Y) in the subpopulations of placental tissue.