McMurray, Cynthia T.

Retinoic acid (RA) is used in differentiation therapy to treat a variety of cancers including neuroblastoma. The basis for its therapeutic efficacy is unknown, however, mitochondria (MT) have been implicated as key effectors in RA‐mediated differentiation process. Here we use the SH‐SY5Y human neuroblastoma cell line as a model to examine the contribution of MT to the physiological effects of RA treatment. We find that RA induces a dramatic increase in the energy metabolism of SH‐SY5Y cells, and shifts the dependence on energy production from glycolysis to oxidative phosphorylation. RA treatment does not increase the number of MT or cause measurable changes in the composition of the electron transport chain. Rather, RA treatment elevates the production of intracellular pyruvate as fuel for mitochondrial consumption, and significantly enhances the mitochondrial respiratory capacity. We propose a competition model for the therapeutic effects of RA. Specifically, the high metabolic rate in differentiated cells limits the availability of metabolic nutrients for use by the undifferentiated cells and suppresses their growth. Thus, RA treatment provides a selective advantage for the differentiated state.

Mammalian cells have evolved sophisticated DNA repair systems to correct mispaired or damaged bases and extra helical loops. However, we find that two DNA repair systems, the mismatch recognition system (MMR) and the base excision repair, are turned into a causative factor rather than a safeguard of genomic integrity. We have followed CAG expansion in germ cells and in somatic tissues of transgenic mice harboring a fragment of the human Huntington's disease (HD) gene. CAG expansion of the hHD allele is abrogated in both somatic cells and in germ cells of transgenic mice that lack Msh2. A complex involving Msh2 is thought to cause expansions by binding to, but failing to correct at the site of DNA breaks. Base excision repair may cause the break that needs to be repaired. Surprisingly, expansion in somatic cells only occurs at midlife of the mouse. These data indicate that some process associated with aging causes expansion and DNA breaks only in midlife. We have purified the MSH2/MSH3 enzymes and examined their biochemical properties. We find that key steps of the MMR system are impaired and that other and repair pathways may be called into play to repair the site.

Abstract Familial expansile osteolysis (FEO) is a rare autosomal dominant disorder characterized by striking focal expansile osteolytic bone lesions and generalized osteopenia, often accompanied by characteristic early hearing loss and dental disease. The TNFRSF11A gene encodes the receptor activator of nuclear factor-κB (RANK), which has been demonstrated to be essential in bone remodeling and osteoclast differentiation. Identical insertional mutations in the first exon of RANK have been identified in all published FEO kindreds. The mutation is an 18 base pair tandem duplication in the sequence coding for the signal peptide of RANK, which causes an increase in NF-κB signaling. We report the identification and mutational analysis of two unrelated FEO patients. One had no family history of FEO, but presented with bilateral hearing loss at an early age, deterioration of teeth, and severe pain and swelling in the distal tibia before the age of 20. The second patient had a family history of FEO and exhibited an extensive expansile tibial lesion and lesions in one humerus and a phalanx. She also had early hearing loss and dental disease. Mutational analysis of the TNFRSF11A gene in our patients demonstrated an 18 base pair tandem duplication, one base proximal to the duplications previously reported. This novel mutation results in addition of the same six amino acids to the RANK signal peptide that has been observed previously. Further analysis of the exon 1 sequence demonstrated that it has the ability to form a stable secondary structure that may facilitate the generation of tandem duplications.