No abstract

The c-MYC oncogene encodes a transcription factor, which is sufficient and necessary for the induction of cellular proliferation. However, the c-MYC protein is a relatively weak transactivator suggesting that it may have other functions. To identify protein interactors which may reveal new functions or represent regulators of c-MYC we systematically identified proteins associated with c-MYC in vivo using a proteomic approach. We combined tandem affinity purification (TAP) with the mass spectral multidimensional protein identification technology (MudPIT). Thereby, 221 c-MYC-associated proteins were identified. Among them were 17 previously known c-MYC-interactors. Selected new c-MYC-associated proteins (DBC-1, FBX29, KU70, MCM7, Mi2-b/CHD4, RNA Pol II, RFC2, RFC3, SV40 Large T Antigen, TCP1a, U5-116kD, ZNF281) were confirmed independently. For association with MCM7, SV40 Large T Antigen and DBC-1 the functionally important MYC-box II region was required, whereas FBX29 and Mi2-b interacted via MYC-box II and the BR-HLH-LZ motif. In addition, regulators of c-MYC activity were identified: ectopic expression of FBX29, an E3 ubiquitin ligase, decreased c-MYC protein levels and inhibited c-MYC transactivation, whereas knock-down of FBX29 elevated the concentration of c-MYC. Furthermore, sucrose gradient analysis demonstrated that c-MYC is present in numerous complexes with varying size and composition, which may accommodate the large number of new c-MYC-associated proteins identified here and mediate the diverse functions of c-MYC. Our results suggest that c-MYC, besides acting as a mitogenic transcription factor, regulates cellular proliferation by direct association with protein complexes involved in multiple synthetic processes required for cell division, as for example DNA-replication/repair and RNA-processing. Furthermore, this first comprehensive description of the c-MYC-associated sub-proteome will facilitate further studies aimed to elucidate the biology of c-MYC.

Mitochondrial DNA mutations play a major role in human aging processes and degenerative diseases. The most frequently reported marker for mutations of the mitochondrial DNA in human skin is a 4977 bp large-scale deletion, called the Common Deletion. Although this deletion is rarely detectable and constitutes only one example of the multitude of about 50,000 known mutations in mitochondrial DNA, it can represent "the tip of the iceberg" of all types of mitochondrial DNA mutations. We established a quantitative real-time polymerase chain reaction assay to detect the Common Deletion in vitro as well as in vivo/ex vivo. In contrast to previous studies, we were able to demonstrate that the Common Deletion is frequently abundant in keratinocytes isolated from various donors. Quantitative analysis of the mutation indicated interperson variations but obviously no relation to the donors' ages. Prolonged proliferation of keratinocytes led to a distinct reduction in the amount of the Common Deletion. Single ultraviolet A irradiation (12 J per cm2 and 15 J per cm2) neither in vitro nor in vivo increased the incidence of the mutation in keratinocytes, whereas repetitive irradiation resulted in a clear increase in vitro. Again, prolonged cultivation of these irradiated cells caused a significant reduction in the amounts of the deletion. In view of these results, the Common Deletion appears to be a useful marker rather for ultraviolet-A-induced alterations than for chronologic aging in human skin keratinocytes.

A 2 years 4 months old boy with erythroleukemia (FAB-M6) and Down's syndrome is described. Chromosome analysis of bone marrow leukemic blasts revealed apart from the trisomy 21 a partial trisomy of the long arm of chromosome 1:1q23-->1qter in all cells and trisomy 8 mosaicism. To the best of our knowledge this is the first time that a partial trisomy of chromosome 1 in association with erythroleukemia has been described. Previous reports of other hematologic malignancies with aberrations of chromosome 1 indicate that the breakpoint 1q23 is nonrandom and that trisomies of chromosome 1 plays a crucial role in the course of development of hematologic malignancies. This could probably also be true for erythroleukemias.