HtrA1 in human urothelial bladder cancer: A secreted protein and a potential novel biomarker

Abstract

Our aim was to analyze the expression of the serine protease HtrA1 in human bladder tissue and urine in order to point out its possible association with the presence of urothelial bladder cancer. Bladder tissue and urine specimens from cancer patients with different tumor grades and stages (n 5 68) and from individuals with cystitis (n 5 16) were collected along with biopsy specimens and urine from healthy individuals (n 5 68). For the first time, we demonstrated by immunohistochemistry that HtrA1 protein is produced by bladder urothelium in both physiological and inflammatory conditions, whereas it is not detectable in urothelial cancer cells regardless of tumor grade and stage. A different HtrA1 expression between normal-looking and neoplastic bladder tissue, despite similar HtrA1 mRNA levels, was also found by western blotting, which disclosed the presence of two forms of HtrA1, a native form of~50 kDa and an autocatalytic form of~38 kDa. Our investigations documented the presence of the two forms of HtrA1 also in urine. The~38 kDa form was significantly down-regulated in neoplastic tissue, whereas significantly higher amounts of both HtrA1 forms were found in urine from cancer patients compared with both healthy subjects and patients with cystitis. Our findings suggest that HtrA1 is a downexpressed molecule since an early stage of bladder urothelial carcinoma development and that urinary HtrA1 protein may be considered, if successfully validated, as an early and highly sensitive and specific biomarker for this neoplasia (the sensitivity and specificity of HtrA1 are 92.65% and 95.59%, respectively).

The serine protease HtrA1 contributes to the formation of an extracellular 25-kDa apolipoprotein E fragment that stimulates neuritogenesis

“…S5D). This is consistent with previous studies that have shown the 38 kDa band is an autocatalytic product of the full length 50 kDa HtrA1 protein (28). Overall, SK-N-SH secreted HtrA1 protein levels were increased by 2.1-fold (p = 0.0002) after 9 days in culture with ATRA (Suppl.…”

Structural insights into the activation mechanisms of human HtrA serine proteases

“…Therefore they proposed that the N-terminal domain may function as a redox-sensing element that regulates autoproteolytic activity of HtrA1 in vivo depending on the cellular redox state [114]. Their conclusion is closely connected to the earlier findings showing that HtrA1 undergoes a limited proteolytic processing [24,115,116]. Chien et al [24] demonstrated that in response to paclitaxel treatment of ovarian cancer cells HtrA1 underwent autocatalytic cleavage resulting in generation of the protease variant lacking the N-terminal domain.…”

“…Although both the full-length HtrA1 and the processed form of the enzyme showed a similar proteolytic activity in vitro, the latter was more active in inducing apoptotic cell death [24]. The processed form of HtrA1 was observed in ovarian cell lines following anoikis-inducing conditions [15] and also in tumor tissues from patients with urothelial bladder cancer [116]. Apart from proving that redox changes influence HtrA1 cleavage in a cell, there still remains an open question, how HtrA1 lacking its N-terminal domain is regulated in vivo.…”

The Autolysis of Human HtrA1 Is Governed by the Redox State of Its N-Terminal Domain

“…17,36 Recently, reduced levels of the autolytic ∼38 kDa product of HtrA1 were found to correlate with neoplastic bladder tissue undergoing cancerous transformation, which indeed highlights the importance of understanding the functional maturation of HtrA1 and the potential prognostic value of the autolytic forms. 28 …”

“…20,21 The specific downregulation of HtrA1 in the latter case promotes the sustained survival of cancer cells and the development of malignant metastatic behavior, 20,22,23 most likely correlated with the intracellular HtrA1 associated with microtubules and affecting cell migratory and signaling properties. 3,14,24−27 Interestingly, autolytically N-terminally truncated forms of HtrA1 exist in vivo , and such forms have been suggested as prognostic markers in urothelial bladder cancer 28 and in preeclamptic pregnancies. 18 The exact role and trigger of autolytic maturation is at present unknown.…”