Untersuchungen zur Funktion der HMGA- und HMGB-Subfamilien bei der Tumorentstehung.

Abstract

Proteins encoded by the genes HMGA1, HMGA2 und HMGB1 are architectural transcription factors whose interaction with DNA lead to a conformational change affecting the assembly of functional multiprotein-complexes.Different benign mesenchymal tumor entities are characterized by chromosomal aberrations within 12q14-15 or 6p21.3 show rearrangements of HMGA2 or HMGA1, respectively.Chromosomal breakpoints affecting HMGA1 were predominantly located within the 3 flanking region leading to the expression of aberrant transcripts. Expression of HMGA1 and HMGA2 is under control of functional elements located within their 3 UTR.Truncation of these elements as found within tumors is associated with an increased expression.The HMGA2 5 flanking region contains two functionally independent promoter and a (TC)-repeat whose repeat length is crucial for expressional activity. A high affinity HMGA2 binding site was mapped within the ERCC1 promoter. Comparison of binding to this region between HMGA2 and C﷓terminally truncated ΔHMGA2 showed that the acidic C-tail had no influence on binding affinity but is associated with differences in pattern, stoichiometry, and mechanisms of DNA-binding. These differences led to a significant change in DNA-conformation and a stronger inhibition of ERCC1 promoter activity due to ΔHMGA2. Expression array analyses of myometrial cells induced by native and aberrant HMGA proteins showed that besides their structural differences the HMGA variants are functionally related to each other. Genes functionally involved in proliferation and differentiation were predominantly down-regulated by HMGA in normal myometrial cells. A new gene (LBH) was mapped in tail-to-tail orientation directly behind HMGA1. Its expression was not significantly altered in tumors with 6p21.3 aberration. Genomic sequence of human HMGB1 was completed and its promoter was functionally characterized. An intertumoral variation of HMGB1 expression was found in breast canc