Proteasome beta subunit pharmacogenomics: gene resequencing and functional genomics.
OBJECTIVE
The proteasome is a multisubunit cellular organelle that functions as a nonlysosomal threonine protease. Proteasomes play a critical role in the degradation of proteins, regulating a variety of cellular processes, and they are also the target for antineoplastic proteasome inhibitors. Genetic variation in proteasome subunits could influence both proteasome function and response to drug therapy.


METHODS
We resequenced genes encoding the three active proteasome beta subunits using 240 DNA samples from four ethnic groups and the beta 5 subunit gene in 79 DNA samples from multiple myeloma patients who had been treated with the proteasome inhibitor bortezomib. Resequencing was followed by functional studies of polymorphisms identified in the coding region and 3'-flanking region (3'-FR) of PSMB5, the gene encoding the target for clinically useful proteasome inhibitors.


RESULTS
Resequencing of 240 DNA samples identified a series of novel ethnic-specific polymorphisms that are not represented in public databases. The PSMB5 3'-FR 1042 G allele significantly increased transcription during reporter gene studies, observations confirmed by genotype-phenotype correlations between single nucleotide polymorphisms (SNP) in PSMB5 and mRNA expression in the 240 lymphoblastoid cell lines from which the resequenced DNA was obtained. Studies with patient DNA samples identified additional novel PSMB5 polymorphisms, including a SNP and an insertion in the 3'-FR. Reporter-gene studies indicated that these two novel polymorphisms might decrease transcription.


CONCLUSIONS
These results show that nonsynonymous coding SNPs in the PSMB5 gene did not show significant effects on proteasome activity, but SNPs did influence transcription. Future studies might focus on regulatory region polymorphisms.
Division of Clinical Pharmacology, Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA. wang.liewei@mayo.edu
Liewei
L
Wang
Shaji
S
Kumar
Brooke L
BL
Fridley
Krishna R
KR
Kalari
Irene
I
Moon
Linda L
LL
Pelleymounter
Michelle A T
MA
Hildebrandt
Anthony
A
Batzler
Bruce W
BW
Eckloff
Eric D
ED
Wieben
Philip R
PR
Greipp
D000595:Amino Acid Sequence; D001483:Base Sequence; D029721:Drosophila Proteins; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D010450:Endopeptidases; D005006:Ethnicity; D015870:Gene Expression; D005786:Gene Expression Regulation; D005787:Gene Frequency; D006239:Haplotypes; D006801:Humans; D008969:Molecular Sequence Data; D009101:Multiple Myeloma / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010597:Pharmacogenetics; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D046988:Proteasome Endopeptidase Complex / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection
D029721:Drosophila Proteins; D010450:Endopeptidases; C514943:Prosbeta2 protein, Drosophila; C088874:PSMB5 protein, human; D046988:Proteasome Endopeptidase Complex