Intron retention: a common splicing event within the human kallikrein gene family.
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 a 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 as 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.
Michael
Iacovos P
IP
Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, ON, Canada.
Kurlender
Lisa
L
Memari
Nader
N
Yousef
George M
GM
Du
Daisy
D
Grass
Linda
L
Stephan
Carsten
C
Jung
Klaus
K
Diamandis
Eleftherios P
EP
D017398:Alternative Splicing; D001483:Base Sequence; D003001:Cloning, Molecular; D006801:Humans; D007438:Introns; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D007610:Kallikreins / Q000096:biosynthesis / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009928:Organ Specificity; D011467:Prostate / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000235:genetics; D020840:Tissue Kallikreins / Q000096:biosynthesis / Q000235:genetics
D007527:Isoenzymes; C501608:KLK15 protein, human; C400147:KLK5 protein, human; D007610:Kallikreins; D012697:Serine Endopeptidases; C120801:kallikrein 4; D020840:Tissue Kallikreins