Human Kallikrein 8 Protease Confers a Favorable Clinical Outcome in Non–Small Cell Lung Cancer by Suppressing Tumor Cell Invasiveness

Abstract

The human kallikrein 8 (KLK8) gene, a member of the human tissue kallikrein gene family, encodes a serine protease. The KLK8 protein (hK8) is known to be a favorable prognostic marker in ovarian cancer, but the biological basis of this is not understood. We found that overexpressing the KLK8 gene in highly invasive lung cancer cell lines suppresses their invasiveness. This role in invasiveness was further confirmed by the fact that inhibition of endogenous KLK8 expression with a specific short hairpin RNA reduced cancer cell invasiveness. In situ degradation and cell adhesion assays showed that proteins produced from KLK8 splice variants modify the extracellular microenvironment by cleaving fibronectin. DNA microarray experiments and staining of cells for actin filaments revealed that the degradation of fibronectin by hK8 suppresses integrin signaling and retards cancer cell motility by inhibiting actin polymerization. In addition, studies in a mouse model coupled with the detection of circulating tumor cells by quantitative PCR for the human Alu sequence showed that KLK8 suppresses tumor growth and invasion in vivo. Finally, studies of clinical specimens from patients with non-small cell lung cancer showed that the time to postoperative recurrence was longer for early-stage patients (stages I and II) with high KLK8 expression (mean, 49.9 months) than for patients with low KLK8 expression (mean, 22.9 months). Collectively, these findings show that KLK8 expression confers a favorable clinical outcome in nonsmall cell lung cancer by suppressing tumor cell invasiveness.

Alternative Splicing Variant of Kallikrein-Related Peptidase 8 as an Independent Predictor of Unfavorable Prognosis in Lung Cancer

“…Our findings concerning the KLK8 mRNA variable are in general agreement with a previous study on the expression of the KLK8 gene in lung cancer (11 ). In both of these studies, the primer set used to evaluate KLK8 gene activity hybridizes with all of the alternative KLK8 gene transcripts, except KLK8-T4 (Table 1).…”

“…These steps include local invasion, intravasation of cells from the primary tumor into the circulatory system, survival of these cells within the blood or lymphatic system, evasion of the immune system, arrest at a secondary site distant from the site of origin, extravasation, initiation of either intra-or extravascular growth within this secondary site, and, finally, maintenance of growth leading to the formation of overt, vascularized, clinically detectable metastases (23 ). Overproduction of type 1 and type 2 KLK8 mRNAs has been shown to decrease the in vitro invasiveness of lung cancer cells (11 ). These protective effects of KLK8-T1 and KLK8-T2 mRNAs have been ascribed to the proteolysis of extracellular fibronectin by the encoded KLK8 peptidase, KLK8-mediated degradation of fibronectin-suppressed integrin signaling, and decreased lung cancer cell motility through inhibition of actin polymerization.…”

“…The KLK8 peptidase is present in numerous human tissues (10 ) and is involved in several physiological and pathologic processes (11,12 ). Abnormal KLK8 transcripts and/or the KLK8 protein have been found in several malignancies, including uterine endometrial carcinoma and ovarian, lung, and neck cancers (11,(13)(14)(15). Five alternative mRNA variants encoded by KLK8, including the regular form, have been described (7 ).…”

Human Kallikrein 8 Expression in Salivary Gland Tumors

“…In non-small cell lung cancer, KLK8 appears to suppress tumor cell invasiveness by degrading fibronectin, thereby suppressing integrin signalling, and also retards cancer cell motility by inhibiting actin polymerization [26]. In a mouse model, KLK8 suppresses tumor growth and invasion in vivo.…”

Kallikrein-related peptidase genes as promising biomarkers for prognosis and monitoring of human malignancies

“…In non-small cell lung cancer, KLK6 and KLK8 expression presents a controversial prognostic impact. In particular, KLK6 expressional status serves as an unfavorable biomarker, opposite to the favorable clinical strength of KLK8 overexpression, which was found to be correlated with longer postoperative recurrence periods (Sher et al, 2006;Nathalie et al, 2009). Moreover, decreased KLK11 mRNA levels were found to correlate significantly with low differentiated adenocarcinomas and poor prognostic outcome (Paliouras et al, 2007).…”