Regulation of the prostaglandin pathway during development of invasive bladder cancer in mice

Abstract

Prostaglandin E 2 (PGE 2 ) is reported to play an important role in tumor development. We explored the differential expression of genes governing production of, and response to, PGE 2 during development of invasive bladder cancer. N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) or vehicletreated mice (n = 4-5) were euthanized after 4-8 weeks (period 1, P1), 12-16 weeks (P2), and 20-23 weeks (P3). Half of each bladder was analyzed histologically and the other half extracted for mRNA analysis by quantitative real-time PCR. Bladders from BBN-treated mice showed progression from submucosal inflammation (P1) to squamous metaplasia/focal CIS (P2) to poorly differentiated, invasive cancer (P3). mRNA levels for the inducible cyclooxygenase, COX-2, were elevated three to fourfold at all time points in BBN-treated mice compared to controls. In contrast, mRNA levels for constitutive COX-1 and cytosolic phospholipase A 2 (cPLA 2 ), which releases substrate for COX, were either unchanged or decreased in BBN-treated mice relative to controls. Downstream of COX, mRNA levels of membrane-bound PGE 2 synthase (mPGES-1) were increased 1.7-fold at P1 in BBN bladders but returned to control levels at P2 and P3. mRNA levels for 15-prostaglandin dehydrogenase (PGDH), which inactivates PGE 2 , were reduced 50-80% in BBN-treated bladders at all time points. mRNA levels for EP2R and EP4R, receptors for PGE 2 , were two to threefold increased at P1, but returned to control levels or below at P3. Hence, increased COX-2 and decreased PDGH expression occurred throughout tumor development, while mPGES-1, EP2R and EP4R were elevated only before development of invasive cancer. We compared expression of these genes in the malignant human urothelial cell lines, HTB-5 and HT-1376, with expression in a benign urothelial cell line, UROtsa. Neither malignant cell line reproduced the complete in vivo pattern, relative to benign cells, but each showed abnormal basal expression of several of the genes downstream of COX-2, but not COX-2 itself. We conclude that components involved in PGE 2 synthesis and activity are differentially regulated during bladder tumor development and the therapeutic efficacy of targeting the various components may vary with stage of tumor development.

Suppressive Effect of Matrine on Tumor Invasion in N-Butyl-N-(4-Hydroxybutyl)Nitrosamine-Induced Urinary Bladder Carcinogenesis

“…The elevated expression of COX-2 and cPLA2, as well as the reduced expression of PGDH, which might increase the production of PGE 2 , have been observed in the pathogenesis of either BBN-initiated or calculus-induced bladder cancer [19,20]. Overexpression of COX-2, a crucial rate-limiting enzyme in PGE 2 biosynthesis, has been reported both in human invasive bladder carcinoma and in carcinogen-induced bladder cancer animal models, respectively [15,17], and inhibition of COX-2 is the most common approach to inhibiting the prostaglandin pathway.…”

“…Additionally, PGDH, which degrades PGE 2 , has been shown to regulate bladder cancer progression. It is well documented that loss of PGDH expression correlates with tumor stage in bladder cancer [33], and a reduced level of PGDH and an increased expression of COX-2 have been noted in the development of bladder carcinogenesis in mice [19], and inhibition of PGDH expression in well-differentiated RT4 cells using small inhibitory RNA or short hairpin RNA has resulted in a lack of E-cadherin assembly and a more aggressive phenotype with increased motility and anchorage-independent growth [34,35]. In line with the previous findings, in our study a reduced expression of PGDH was observed in BBN-induced rat bladder carcinomas.…”

“…Due to morphological, biological, and molecular parallels with human bladder cancer, it has been used as an appropriate and validated model for study of the pathophysiology of bladder carcinogenesis, as well as novel alternatives for therapeutic intervention [6,7,8,9]. It is well documented that the prostaglandin pathway plays a key role in bladder cancer, and alterations in this pathway are the most important molecular and cellular mechanisms for bladder carcinogenesis [10,11,12]. The inducible cyclooxygenase-2 (COX-2) is a key rate-limiting enzyme in prostaglandin biosynthesis [13,14].…”

“…Overexpression of COX-2 is found in carcinogen-induced bladder cancers, and treatment with COX-2 inhibitors such as celecoxib, meloxicam, and nimesulide has been shown to inhibit tumor development [15,16,17,18]. Moreover, an altered expression of other potential targets, such as cytosolic phospholipase A2 (cPLA2) and prostaglandin dehydrogenase (PGDH), has also been found in bladder cancer developed in carcinogen-treated mice and rats [11,12,19,20]. Thus, modulation of the prostaglandin pathway is expected to be effective in chemoprevention of bladder cancer.…”

Loss of 15-Hydroxyprostaglandin Dehydrogenase Expression Contributes to Bladder Cancer Progression

“…More recently, a study of mouse bladder cancer chemical carcinogenesis showed that COX2 expression was increased while PGDH levels reduced as bladder cancers developed. 17 Work from our laboratory showed that small inhibitory RNA (siRNA) inhibition of PGDH expression in the well-differentiated RT4 human bladder cancer cell line disrupts E-cadherin complex assembly. 18 Thus, a more detailed study of PGDH expression in bladder cancer is warranted.…”