Splice donor site mutations in the 3-hydroxy-3-methylglutaryl coenzyme A reductase gene cause a deficiency of the endoplasmic reticulum 3-hydroxy-3-methylglutaryl coenzyme A reductase protein in UT2 cells.

UT2 cells are a mutant clone of Chinese hamster ovary (CHO) cells that are deficient in the 97 kDa endoplasmic reticulum (ER) 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase protein. The analysis of UT2 cell cDNA and genomic DNA has led to the identification of two novel point mutations in intronic sequences of the ER HMG-CoA reductase gene. One mutation identified at the +1 position (G --> A) of the 5' splice site of exon 11-12 junction was shown to cause exon 11 skipping which resulted in the insertion of premature stop codons. We also identified a second mutation at the +5 position (G --> A) of the 5' splice site in the intron spanning exons 13 and 14. Furthermore, the data indicate that the two mutations in the reductase gene are present on the same allele. As demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) of UT2 cell mRNA, the mutations produce aberrant spliced messages. If the aberrant messages were translated, truncated proteins of 44 kDa or 66 kDa would be predicted. More importantly, these truncated proteins would be expected not to have catalytic activity. In addition, we have also recently demonstrated that the UT2 cells express a 90 kDa HMG-CoA reductase protein that is localized exclusively in peroxisomes, and is up-regulated when the cells are grown in the absence of added mevalonate. Thus, the mutations identified in the ER reductase gene in UT2 cells indicate that neither a 97 kDa nor a 90 kDa reductase protein can be produced from this gene.