Expression and localization of mesothelin in developing rat pancreas

Mesothelin promotes cell proliferation in the remodeling of neonatal rat pancreas

AIM: To investigate the effect of mesothelin in the remodeling of the endocrine pancreas in neonatal rats.

METHODS: Overexpression or downregulation of mesothelin expression in INS-1 cells was carried out to investigate the effect of mesothelin during cell proliferation and cell apoptosis in vitro. Adenovirus-mediated RNA interference was performed to block mesothelin in vivo to directly assess the role of mesothelin in the remodeling of the endocrine pancreas in neonatal rats.

RESULTS: Exogenous overexpression of mesothelin promoted cell proliferation, cell colony formation and enhanced cell resistance to apoptosis of INS-1 cells. Down-regulation of mesothelin made no difference in cell proliferation and apoptosis compared with that in the control group. After an injection of adenovirus-mesothelin, a significantly increased number of small islets appeared, and the expression of PCNA was decreased on day 7 and day 14 compared with the Ad-EGFP group.

CONCLUSION: Mesothelin was able to promote β cell proliferation in the remodeling stage of neonatal rats. Mesothelin may have an important role in the remodeling of the endocrine pancreas in neonatal rats.

Mesothelin confers pancreatic cancer cell resistance to TNF-α-induced apoptosis through Akt/PI3K/NF-κB activation and IL-6/Mcl-1 overexpression

Background

Previous studies showed that mesothelin (MSLN) plays important roles in survival of pancreatic cancer (PC) cells under anchorage dependent/independent conditions as well as resistance to chemotherapy. The recent success of intratumorally-injected adeno-encoded, chemo/radiation-inducible-promoter driven hTNF-α, (TNFerade) + gemcitabine in pre-clinical models of PC have renewed interest in use of TNF-α as a therapeutic component. To help find additional factors which might affect the therapy, we examined the resistance of MSLN-overexpressing pancreatic cancer cell lines to TNF-α-induced growth inhibition/apoptosis.

Methods

Stable MSLN overexpressing MIA PaCa-2 cells (MIA-MSLN), stable MSLN-silenced AsPC-1 cells (AsPC-shMSLN) and other pancreatic cells (MIA-PaCa2, Panc 28, Capan-1, BxPC3, PL 45, Hs 766T, AsPC-1, Capan-2, Panc 48) were used. NF-κB activation was examined by western blots and luciferase reporter assay. TNF-α induced growth inhibition/apoptosis was measured by MTT, TUNEL assay and caspase activation. IL-6 was measured using luminex based assay.

Results

Compared to low endogenous MSLN-expressing MIA PaCa-2 and Panc 28 cells, high endogenous MSLN-expressing Capan-1, BxPC3, PL 45, Hs 766T, AsPC-1, Capan-2, Panc 48 cells were resistant to TNF-α induced growth inhibition. Stable MSLN overexpressing MIA-PaCa2 cells (MIA-MSLN) were resistant to TNF-α-induced apoptosis while stable MSLN-silenced AsPC1 cells (AsPC-shMSLN) were sensitive. Interestingly, TNF-α-treated MIA-MSLN cells showed increased cell cycle progression and cyclin A induction, both of which were reversed by caspase inhibition. We further found that MIA-MSLN cells showed increased expression of anti-apoptotic Bcl-XL and Mcl-1; deactivated (p-Ser⁷⁵) BAD, and activated (p-Ser⁷⁰) Bcl-2. Constitutively activated NF-κB and Akt were evident in MIA-MSLN cells that could be suppressed by MSLN siRNA with a resultant increase in sensitivity of TNF-α induced apoptosis. Blocking NF-κB using IKK inhibitor wedelolactone also increased sensitivity to TNF-α-mediated cytotoxicity with concomitant decrease in Mcl-1. Blocking Akt using PI3K inhibitor also had a likewise effect presumably affecting cell cycle. MIA-MSLN cells produced increased IL-6 and were increased furthermore by TNF-α treatment. SiRNA-silencing of IL-6 increased TNF-α sensitivity of MIA-MSLN cells.

Conclusions

Our study delineates a MSLN-Akt-NF-κB-IL-6-Mcl-1 survival axis that may be operative in PC cells, and might help cancer cells' survival in the highly inflammatory milieu evident in PC. Further, for the success of TNFerade + gemcitabine to be successful, we feel the simultaneous inhibition of components of this axis is also essential.

Streptozotocin-induced expression of Ngn3 and Pax4 in neonatal rat pancreatic α-cells

AIM: To investigate the mechanism behind β-cell regeneration in neonatal rat pancreas treated with streptozotocin (STZ).

METHODS: Neonatal Sprague Dawley rats were intraperitoneally injected with 70 mg/kg STZ. Body weight, pancreas weight and blood glucose were recorded every two days after the treatment. To identify the expression and location of transcription factors in the rat pancreas, double immunofluorescent staining was performed using antibodies to specific cell markers and transcription factors.

RESULTS: Expression of Neurogenin 3 (Ngn3), a marker for endocrine precursor cells, was observed by immunofluorescence in a few β-cells and many α-cells. The expression reached a peak 12 d after treatment. Pax4, a transcription factor that lies downstream of Ngn3 and plays an important role in β-cell differentiation, was also expressed in the α-cells of STZ-treated rats. We did not observe significant changes in Nkx6.1, which is essential for β-cell maturation in the treated rats.

CONCLUSION: α-cells dedifferentiated into endocrine precursor cells and acquired the ability to dedifferentiate in the neonatal rat pancreas after STZ treatment.

Expression and localization of Wolfram syndrome 1 gene in the developing rat pancreas

AIM: To investigate the expression and function of Wolfram syndrome 1 gene (WFS1) during the development of normal pancreas.

METHODS: Pancreas from Sprague-Dawley rat fetuses, embryos, young and adult animals were used in this study. Expression levels of WFS1 in pancreas of different development stages were detected by reverse transcription-polymerase chain reation (RT-PCR) and Western blotting. To identify the cell location of WFS1 in the developing rat pancreas, double-immunofluorescent staining was performed using antibodies to specific cell markers and WFS1, respectively.

RESULTS: Compared to E15.5, the highest level of WFS1 mRNA was detected at E18.5, the level of WFS1 mRNA in E15.5 and P0 was less, and at a lowest at adult (P < 0.05 vs P0 and adult), respectively. Compare to E15.5, the highest level of WFS1 was at P14 and lowest at P21 (P < 0.05 vs P14 and P21), respectively. The WFS1 positive staining is expressed in the normal developing rat pancreas mainly in the islet beta-cells and mesenchyme at each stage tested.

CONCLUSION: These results indicate that WFS1 may be involved in some aspects of pancreatic development and further research on WFS1 may provide new evidences to prove the interactions between mesenchyma and epithelia at the same time.