The Kallikrein Gene 5 Splice Variant 2 Is a New Biomarker for Breast and Ovarian Cancer

Abstract

The presence of more than one mRNA form for the same gene is common among kallikreins, and many of the kallikrein splice variants may hold significant clinical value. The human kallikrein gene 5 (KLK5) is a member of the human kallikrein gene family of serine proteases on chromosome 19q13.4. KLK5 has been shown to be differentially expressed in a variety of endocrine tumors including ovarian, breast and prostate cancer. Utilizing Expressed Sequence Tag database analysis and reverse transcriptase polymerase chain reaction, we identified a new alternatively spliced form of KLK5(KLK5-splice variant 2, KLK5-SV2). This variant mRNA is 1,438 bp in length; formed of 195 bp of 5′ untranslated region, 882 bp of protein coding sequence and a 3′ untranslated region of 326 nucleotides. KLK5-SV2 has 7 exons, the first 2 of which are untranslated, and 6 intervening introns. KLK5-SV2 is different from the classic form of the KLK5 mRNA in its 5′ untranslated region, where the first 5′ untranslated exon of the classic form is split into 2 exons with an intervening intron of 135 nucleotides. KLK5-SV2 is expressed in a variety of tissues, with higher expression levels in the mammary gland, cervix, salivary gland and trachea. The steroid hormone receptor-positive breast cancer cell line BT-474 was used to examine the effect of different steroids on the expression levels of KLK5-SV2. Expression levels were significantly higher after stimulation with androgens, but not estrogens, progestins, aldosterone or corticosteroids. While relatively high levels of expression were found in all 10 normal breast tissues examined, no expression was detected in 16 breast cancer tissues, and expression was significantly lower than normal in the remaining 4 cancers. Expression levels comparable to normal were found in only 1 breast cancer cell line. Weak to no expression was detected in 3 other breast cancer cell lines. KLK5-SV2 was not detectable in any of the 10 normal ovarian tissues examined. It was, however, expressed at relatively high levels in 10 out of 20 ovarian cancer tissues, and lower levels were found in 4 other cancers. No expression was detected in the remaining 6 cancers. High expression levels were also detected in the CAOV-3 ovarian cancer cell line. KLK5-SV2 is a potential biomarker for breast and ovarian cancers.

Kallikreins on Steroids: Structure, Function, and Hormonal Regulation of Prostate-Specific Antigen and the Extended Kallikrein Locus

“…KLK2, 3,8,10,11,13,14, and 15 are all up-regulated by androgens at the mRNA and protein level in breast cancer cell lines (223,(392)(393)(394)(395)(396). Based on qualitative RT-PCR, KLK4, 5, 6, 9, and 12 expression may also be stimulated by androgens in breast cancer cell lines, but these observations require further validation (71, 223,389,397,398). Notably, KLK3 has been detected in 98% of breast cancer specimens that express AR (399).…”

Kallikrein-related peptidase 5 induces miRNA-mediated anti-oncogenic pathways in breast cancer

“…The potential utility of KLK5 as a cancer biomarker has been reported. Reduced expression of KLK5 has been observed in breast cancers[ 9 , 28 ], and in malignant compared to benign breast tissue [ 29 ]. KLK5 is also found to be down-regulated in pancreatic [ 30 ], prostate [ 31 ], lung [ 32 ], testicular [ 33 ], and renal cancers [ 34 ], pointing to a tumor suppressor function.…”

A Kallikrein 15 (KLK15) single nucleotide polymorphism located close to a novel exon shows evidence of association with poor ovarian cancer survival

“…This isoform utilizes exon B instead of exon 1 and is predicted to have a different function by encoding a protein lacking a signal peptide. Alternative KLK transcripts may possess both physiological and prognostic significance and some are emerging candidate biomarkers [ 25 , 33 , 34 ]. For example, the PSA-RP2 [ 35 ] and KLK15 isoform 3 [ 11 , 36 ] are upregulated in prostate cancer compared with benign prostatic hyperplasia tissues suggesting that differential mRNA splicing may be an important regulatory event in carcinogenesis.…”