Elucidating the Role of Pro-renin Receptors in Pancreatic Ductal Adenocarcinoma Progression: A Novel Therapeutic Target in Cancer Therapy

Pancreatic cancer is a highly aggressive malignancy with a very poor prognosis. The 5- year survival in these patients is very low, and most patients develop drug resistance to current therapies, so additional studies are needed to identify the potential role of new drug targets for the treatment of pancreatic cancer. Recent investigations have been performed regarding the roles of pro-renin receptors (PRR) in the initiation and development of cancers. PRR is a component of the local renin-angiotensin system (RAS). Local tissue RAS has been known in diverse organ systems, including the pancreas. Various investigations have implicated that PRRs are associated with the upregulation of various signaling pathways, like the renin-angiotensin system pathway, PI3K/Akt/mTOR, and the Wnt-signaling pathways, to contribute to pathological conditions, including cancer. In this review, we presented an overview of the role of PRR in the progression of pancreatic adenocarcinoma.

Expression of Components of the Renin-Angiotensin System by Cancer Stem Cells in Renal Clear Cell Carcinoma

This study investigated the expression of components of the renin-angiotensin system (RAS) by cancer stem cells (CSCs) we have recently demonstrated in renal clear cell carcinoma (RCCC). Fifteen RCCC tissue samples underwent immunohistochemical staining for components of the RAS: renin, pro-renin receptor (PRR), angiotensin-converting enzyme (ACE), angiotensin-converting enzyme 2 (ACE2), and angiotensin II receptor 2 (AT₂R). Immunofluorescence co-staining or double immunohistochemical staining of these components of the RAS with stemness-associated markers OCT4 or KLF4 was performed on two of the samples. Protein and transcript expression of these components of the RAS in six RCCC tissue samples was investigated using western blotting and reverse transcription quantitative polymerase chain reaction (RT-qPCR), respectively. In addition, angiotensin II receptor 1 (AT₁R) was investigated using RT-qPCR only. Immunohistochemical staining demonstrated expression of renin, PRR, and ACE2 in 11, 13, and 13 out of 15 RCCC samples, respectively, while AT₂R was expressed in all 15 samples. ACE was detected in the endothelium of normal vasculature only. Double immunohistochemical staining demonstrated localization of ACE2, but not renin, to the KLF4+ CSCs. Immunofluorescence staining showed localization of PRR and AT₂R to the OCT4+ CSCs. Western blotting confirmed protein expression of all components of the RAS except renin. RT-qPCR demonstrated transcript expression of all components of the RAS including AT₁R, but not AT₂R, in all six RCCC tissue samples. This study demonstrated expression of PRR, ACE2, and AT₂R by the CSCs within RCCC. Further studies may lead to novel therapeutic targeting of CSCs by manipulation of the RAS in the treatment of this aggressive cancer.

Cancer Stem Cells in Head and Neck Metastatic Malignant Melanoma Express Components of the Renin-Angiotensin System

Components of the renin-angiotensin system (RAS) are expressed by cancer stem cells (CSCs) in many cancer types. We here investigated expression of the RAS by the CSC subpopulations in human head and neck metastatic malignant melanoma (HNmMM) tissue samples and HNmMM-derived primary cell lines. Immunohistochemical staining demonstrated expression of pro-renin receptor (PRR), angiotensin-converting enzyme (ACE), and angiotensin II receptor 2 (AT₂R) in all; renin in one; and ACE2 in none of the 20 HNmMM tissue samples. PRR was localized to cells within the tumor nests (TNs), while AT₂R was expressed by cells within the TNs and the peritumoral stroma (PTS). ACE was localized to the endothelium of the tumor microvessels within the PTS. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) detected transcripts for PRR, ACE, ACE2, and AT₁R, in all the five HNmMM tissue samples and four HNmMM-derived primary cell lines; renin in one tissue sample and one cell line, and AT₂R in none of the five HNmMM tissue samples and cell lines. Western blotting showed variable expression of ACE, PRR, and AT₂R, but not ACE2, in six HNmMM tissue samples and two HNmMM-derived primary cell lines. Immunofluorescence staining of two HNmMM tissue samples demonstrated expression of PRR and AT₂R by the SOX2+ CSCs within the TNs and the OCT4+ CSCs within the PTS, with ACE localized to the endothelium of the tumor microvessels within the PTS.

Pro-Renin Receptor Overexpression Promotes Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Apolipoprotein E-Knockout Mice

The pro-renin receptor (PRR) is an important novel component of the renin-angiotensin (Ang) system that has multiple functions, which are not yet completely understood. In this study, we aimed to explore the effect of PRR on the formation of Ang II-induced abdominal aortic aneurysm (AAA) in apolipoprotein E-knockout mice. We used Ang II (1.44 mg/kg/day) infusion to induce AAA followed by a treatment of saline, telmisartan, no treatment, Ad-EGFP, Ad-PRR, or Ad-PRR plus telmisartan. The incidence of AAA was 35%, 60%, 65%, 90%, and 55% in the Telmisartan, Vehicle, Ad-EGFP, Ad-PRR, and Ad-PRR+Telmisartan groups, respectively. Compared with the Vehicle and Ad-EGFP groups, PRR overexpression markedly increased macrophage infiltration; levels of proinflammatory cytokines, including monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-α (TNF-α); the expression and activity of MMP2 and MMP9; NOX2 and NOX4 protein and mRNA expression; nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity; extracellular-signal-regulated kinase (ERK) and P38MAPK expression; but decreased smooth muscle cells content in AAA. However, telmisartan reversed the adverse effects of PRR. In addition, ERK inhibitor PD98059 eliminated the acceleration of Ang II-induced AAA formation by PRR, and coadministration of telmisartan and PD98059 further abolished the adverse effects of PRR on Ang II-induced AAA formation. Thus, PRR plays an important role in the pathological development of AAA via both Ang II-dependent and Ang II-independent activation of ERK pathways. These results suggest that inhibition of PRR activation may be a promising approach to the treatment of AAA.

Upregulation of Cortical Renin and Downregulation of Medullary (Pro)Renin Receptor in Unilateral Ureteral Obstruction

Chronic kidney disease (CKD) is characterized by renal dysfunction, which is a common feature of other major diseases, such as hypertension and diabetes. Unilateral ureteral obstruction (UUO) has been used as a model of CKD in experimental animals and consists of total obstruction of one kidney ureter. The UUO decreases renal blood flow, which promotes the synthesis of renin in the juxtaglomerular apparatus, the first step in renin–angiotensin system (RAS) cascade. RAS induces inflammation and remodeling, along with reduced renal function. However, it remains unknown whether intrarenal RAS (iRAS) is activated in early stages of CKD. Our objective was to characterize different iRAS components in the renal cortex and in the medulla in an early phase of UUO. Male C57BL/6 mice (8–12 weeks old) were subjected to UUO in the left kidney, or to sham surgery, and were euthanized after 7 days (n = 5/group). Renal function, renal inflammatory/remodeling processes, and iRAS expression were evaluated. UUO increased plasma creatinine, right renal hypertrophy (9.08 ± 0.31, P < 0.05 vs. Sham), and tubular dilatation in the left kidney cortex (42.42 ± 8.19µm, P < 0.05 vs. Sham). This correlated with the increased mRNA of IL-1β (1.73 ± 0.14, P < 0.01 vs. Sham, a pro-inflammatory cytokine) and TGF-β1 (1.76 ± 0.10, P < 0.001 vs. Sham, a pro-fibrotic marker). In the renal cortex of the left kidney, UUO increased the mRNA and protein levels of renin (in 35% and 28%, respectively, P < 0.05 vs. Sham). UUO decreased mRNA and protein levels for the (pro)renin receptor in the renal medulla (0.67 ± 0.036 and 0.88 ± 0.028, respectively, P < 0.05 vs. Sham). Our results suggest that modulation of iRAS components depends on renal localization and occurs in parallel with remodeling and pro-inflammatory/pro-fibrotic mechanisms.