No abstract

HSP90AB1 (heat shock protein 90 kDA alpha, class B, member 1), also known as HSP90beta, is a member of the large family of HSPs which function as molecular chaperones. Chaperones, by binding to client proteins, support proper protein folding and maintain protein stability, especially after exposure to various kinds of cellular stress. Client proteins belong to various protein families including kinases, ubiquitin ligases and transcription factors. HSP90 proteins act as dimers and bind clients with the help of co-chaperones. The cochaperones influence many functions including client binding, ATPase activity or ATP binding of HSP90. HSPs are necessary for a large scale of cellular processes and therefore essential for cell survival. Since client proteins can be mutant proteins that would be degraded without the help of chaperones, HSPs also promote tumor formation and cancer cell proliferation. As such, they are also targets for new therapeutic approaches in cancer treatment. This review focuses on recent studies on HSP90AB1, if possible in comparison with its close homologue HSP90AA1.

a Nucleotide positions (Ϫ16000) between nt 16090 and 16375, different from the Cambridge Reference Sequence (Anderson et al. 1981). Mutations are transitions (T↔C, A↔G), unless the base change is specified explicitly.

The activation of the RET signaling pathway during embryogenesis is a crucial prerequisite for a directional migration of enteric nervous system progenitor cells. Loss-of-function germline mutations of the RET proto-oncogene are reported in familial and sporadic cases of Hirschsprung disease (HSCR) with a variable frequency. Furthermore, variants of several RET polymorphisms are over- or under-represented in HSCR populations. Specifically, the c.135A RET variant has been previously shown to be strongly associated with the HSCR phenotype. We have reported an HSCR-phenotype modifying effect of the RET c.135G>A polymorphism due to a within-gene interaction in patients harboring RET germline mutations, yet the function of the c.135G>A variant is unknown. The basic RET promoter region was investigated by DNA sequencing approach in 80 HSCR patients. Identified polymorphisms were genotyped in the HSCR and in a control population and haplotypes were reconstructed. The dual-luciferase assay was used to evaluate the activity of different RET promoter haplotypes. We demonstrate that variants of two RET promoter polymorphisms -5G>A and -1C>A from the transcription start site are associated with HSCR. Furthermore, the -5G>A polymorphism is in strong linkage disequilibrium with the c.135G>A polymorphism. The promoter haplotype -5/-1AC associated with HSCR has a significantly lower activity in an in vitro dual-luciferase expression assay compared with those haplotypes identified in the majority of normal controls. These data suggest a role for RET haplotypes containing the -5A promoter variant in the etiology of HSCR.