Received on September 7, 2004
Accepted on December 7, 2004

Molecular Diagnostics and Genetics

Intron Retention: A Common Splicing Event within the Human Kallikrein Gene Family

¹ Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, ON, Canada, and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
² Discipline of Pathology, Memorial University, St. John's, NL, Canada
³ Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, ON, Canada
⁴ Urology, University Hospital Charité, Humboldt University, Berlin, Germany

^* To whom correspondence should be addressed. E-mail: ediamandis{at}mtsinai.on.ca.

Background: All human kallikrein (KLK) genes have at least one splice variant, some of which possess clinical utility in cancer diagnostics/prognostics. Given that introns <100 bp in length are retained in 95% of human genes and that splice variants of KLK3 and KLK4 retain intron III, we hypothesized that other proteins in this family, with small intron III, may also retain it.

Methods: Variant-specific reverse transcription-PCRs (RT-PCRs) for KLK1, KLK2, KLK5, and KLK15 were used to identify and clone the full coding sequence of intron III-containing splice variants. In addition, variant-specific RT-PCRs for the cloned KLK3 and KLK4 variants as well for the classical forms of the six genes were used to determine their expression profiles in healthy tissues, their regulation by steroids, and their differential expression in prostate cancer.

Results: KLK1, KLK2, KLK3, KLK4, KLK5, and KLK15 showed a common type of splice variant in which intron III is retained. Expression profiling of these splice variants revealed expression profiles similar to those of the classical mRNA forms, although the pattern of hormonal regulation was different. The KLK15 splice variant was up-regulated in 8 of 12 cancerous prostate tissues. All encoded variant proteins were predicted to be truncated and catalytically inactive because of a lack of the serine residue of the catalytic triad.

Conclusions: The first six centromeric members of the KLK gene family have splice variants that retain intron III. Some variants show tissue-specific expression. The KLK15 splice variant appears to be a candidate biomarker for prostate cancer.