In-silico analysis of kallikrein gene expression in pancreatic and colon cancers.

Human kallikreins are a cluster of 15 serine protease genes located in the chromosomal band 19q13.4, a non-randomly rearranged region in many solid tumors, including pancreatic cancer. We utilized the SAGE and EST databases of the Cancer Genome Anatomy Project to perform in-silico analysis of kallikrein gene expression in normal and cancerous pancreatic and colon tissues and cell lines using virtual Northern blotting (VNB), digital differential display (DDD) and X-profiler. At least two kallikreins, KLK6 and KLK10, are significantly up-regulated in pancreatic cancer. We probed 2 normal and 6 pancreatic cancer SAGE libraries with gene-specific tags for each of these kallikreins. KLK6 was found to be expressed in 5/6 cancer libraries and showed the most marked (5-fold) increase in average expression levels in cancer vs. normal. These data were verified by screening the EST databases, where all mRNA clones isolated were from cancerous libraries, with no clones detected in normal pancreatic tissues or cell lines. X-profiler comparison of two pools of normal and cancerous pancreatic libraries further verified the significant increase of KLK6 expression levels in pancreatic cancer. DDD data showed a 13-fold increase in KLK10 expression in pancreatic cancer. Three kallikrein genes, KLK6, 8 and 10 are overexpressed in colon cancer compared to normal colon, while one kallikrein, KLK1, is down-regulated. While no expression of KLK6 was detected in normal colon, KLK6-specific tags were detectable in 2 cancer libraries. Similar results were obtained by EST screening; no KLK6 clones were detected in any of the 28 normal libraries examined, while 10 KLK6 EST clones were found in colon adenocarcinoma. KLK10 was not detectable in normal colon. Gene-specific tags were, however, detectable with high density in colon cancer and 7 EST clones were found to be expressed in colon Adenocarcinoma.

The human kallikrein protein 5 (hK5) is enzymatically active, glycosylated and forms complexes with two protease inhibitors in ovarian cancer fluids.

The kallikrein family is a group of 15 serine protease genes clustered on chromosome 19q13.4. Binding of kallikreins to protease inhibitors is an important mechanism for regulating their enzymatic activity and may have potential clinical applications. Human kallikrein gene 5 (KLK5) is a member of this family and encodes for a secreted serine protease (hK5). This kallikrein was shown to be differentially expressed at the mRNA and protein levels in diverse malignancies. Our objective was to study the enzymatic activity and the interaction of recombinant hK5 protein with protease inhibitors. Recombinant hK5 protein was produced in yeast and mammalian expression systems and purified by chromatography. HPLC fractionation, followed by ELISA-type assays, immunoblotting and radiolabeling experiments were performed to detect the possible interactions between hK5 and proteinase inhibitors in serum. Enzymatic deglycosylation was performed to examine the glycosylation pattern of the protein. The enzymatic activity of hK5 was tested using trypsin and chymotrypsin-specific synthetic fluorogenic substrates. In serum and ascites fluid, in addition to the free ( approximately 40 kDa) form, hK5 forms complexes with alpha(1)-antitrypsin and alpha(2)-macroglobulin. These complexes were detected by hybrid ELISA-type assays using hK5-specific coating antibodies and inhibitor detection antibodies. The ability of hK5 to bind to these inhibitors was further verified in vitro. Spiking of serum samples with 125I-labeled hK5 results in the distribution of the protein in two higher molecular mass (bound) forms, in addition to the unbound form. The hK5 mature enzyme is active and shows trypsin, but not chymotrypsin-like, activity. The pro-form of hK5 is not active. Recombinant hK5 shows a higher than predicted molecular mass due to glycosylation. hK5 is partially complexed with alpha(1)-antitrypsin and alpha(2)-macroglobulin in serum and ascites fluid of ovarian cancer patients. The recombinant protein is glycosylated and its mature form shows trypsin-like activity.

Differential expression of the human kallikrein gene 14 (KLK14) in normal and cancerous prostatic tissues.

BACKGROUND: Many members of the human kallikrein gene family are differentially expressed in cancer and a few have potential as diagnostic/prognostic markers. KLK14 is a newly discovered human kallikrein gene that is mainly expressed in the central nervous system and endocrine tissues. Since KLK14 was found to be regulated by steroid hormones in prostate cancer cell lines, we hypothesized that it will be differentially expressed in prostate cancer tissues compared to their normal counterparts. METHODS: Matched prostate tissue samples from the cancerous and non-cancerous parts of the same prostates were obtained from 100 patients who underwent radical prostatectomy. Quantitative analysis of KLK14 expression levels were performed by real-time RT-PCR using SYBR Green I dye on the LightCycler trade mark system. Associations with clinico-pathological parameters were analyzed. RESULTS: KLK14 overexpression in the cancerous compared to non-cancerous tissue was found in 74% of patients (P < 0.001). Mean level of expression was 154 arbitrary units (Au) in cancerous tissues and 14.2 Au in the non-cancerous tissues. The ratio of the cancerous to non-cancerous KLK14 expression values was higher in patients with late stage (stage III) compared to stage II (P = 0.002), and in grade 3 compared to grade 1/2 tumors (P = 0.001). A statistically significant increase was also observed in patients with higher in Gleason score (>6) compared to Gleason score = 6 tumors (P = 0.027). No correlation was found between KLK14 tissue expression levels and serum prostate-specific antigen. CONCLUSIONS: KLK14 expression is significantly higher in cancerous compared to non-cancerous prostatic tissue. The up-regulation of the KLK14 gene in advanced and more aggressive tumors may indicate a possible role for the hK14 protein in tumor spread and opens the possibility of hK14 being a candidate new marker for prostate cancer diagnosis and prognosis.

Human kallikrein 5: a potential novel serum biomarker for breast and ovarian cancer.

The kallikrein family is a group of 15 serine protease genes clustered on chromosome 19q13.4. Human kallikrein (hK) gene 5 (KLK5) is a member of this family and encodes for a secreted serine protease (hK5). KLK5 was shown to be differentially expressed at the mRNA level in breast and ovarian cancer. Until now, detection of hK5 protein in either biological fluids or tissues has not been described due to lack of suitable reagents and methods. The aim of this study was to develop immunological reagents and a sensitive and specific fluorometric immunoassay (ELISA) for hK5, to examine the presence of hK5 in human tissues and biological fluids, and to study the possible clinical utility of hK5 as a biomarker for endocrine-related malignancies. Recombinant hK5 protein was produced and purified using a Pichia pastoris yeast expression system. The protein was used as an immunogen to generate mouse and rabbit polyclonal anti-hK5 antibodies. A sandwich-type microplate immunoassay (ELISA) was developed using these antibodies, coupled with a time-resolved fluorometric detection technique. The ELISA assay was then used to measure hK5 in various biological fluids, tissue extracts, and serum samples from normal individuals and patients with various malignancies. The hK5 ELISA immunoassay has a lower detection limit of 0.1 micro g/liter, is specific for hK5, and has no cross-reactivity with other homologous kallikreins. The dynamic range is 0.1-25 micro g/liter, and within-run and between-run coefficients of variation within this range are <10%. hK5 is found in many tissues, with the highest expression levels seen in the skin, breast, salivary gland, and esophagus. hK5 is present at relatively high levels in milk of lactating women. Whereas the levels of hK5 are almost undetectable in serum of normal individuals (male and female) and patients with diverse malignancies, higher concentrations were found in a proportion of patients with ovarian (69%) and breast (49%) cancer. High levels were also detected in ascites fluid from metastatic ovarian cancer patients and in ovarian cancer tissue extracts. In conclusion, we report development of the first immunofluorometric assay for hK5 and describe the distribution of hK5 in biological fluids and tissue extracts. Our preliminary data indicate that hK5 is a potential biomarker in patients with ovarian and breast cancer.

Parallel overexpression of seven kallikrein genes in ovarian cancer.

Recent evidence suggests that many members of the human kallikrein (KLK) gene family are differentially regulated in ovarian cancer and have potential as diagnostic and/or prognostic markers. We used the serial analysis of gene expression and expressed sequence tag databases of the Cancer Genome Anatomy Project to perform in silico analyses of the expression pattern of the 15 human KLK genes in normal and cancerous ovarian tissues and cell lines. We found that seven KLK genes (KLK5, KLK6, KLK7, KLK8, KLK10, KLK11, and KLK14) are up-regulated in ovarian cancer. Probing 2 normal and 10 ovarian cancer serial analysis of gene expression libraries with gene-specific tags for each KLK indicated that whereas no expression was detected in any normal libraries (with the exception of KLK10 and KLK11), these KLKs were found to be expressed with moderate densities (103-408 tags per million) in 40-60% of the ovarian cancer libraries analyzed. These data were verified by screening the expressed sequence tag databases, where 78 of 79 mRNA clones isolated for these genes were from ovarian cancer libraries. X-profiler comparison of the pools of normal and cancerous ovaries identified a significant difference in expression levels for six of the seven KLKs. We experimentally verified the overexpression of six KLK proteins in cancer versus normal or benign tissues with highly sensitive and specific immunofluorometric assays. A statistically significant stepwise increase in protein levels was found among normal, benign, and cancerous ovarian tissues. The expression of five KLKs showed a strong degree of correlation at the protein level, suggesting the existence of a common mechanism or pathway that controls the expression of this group of adjacent genes during ovarian cancer progression.