New gene expressed in prostate: a potential target for T cell-mediated prostate cancer immunotherapy

New gene expressed in prostate (NGEP) is a prostate-specific gene encoding either a small cytoplasmic protein (NGEP-S) or a larger polytopic membrane protein (NGEP-L). NGEP-L expression is detectable only in prostate cancer, benign prostatic hyperplasia and normal prostate. We have identified an HLA-A2 binding NGEP epitope (designated P703) which was used to generate T cell lines from several patients with localized and metastatic prostate cancer. These T cell lines were able to specifically lyse HLA-A2 and NGEP-expressing human tumor cells. NGEP-P703 tetramer binding assays demonstrated that metastatic prostate cancer patients had a higher frequency of NGEP-specific T cells when compared with healthy donors. Moreover, an increased frequency of NGEP-specific T cells was detected in the peripheral blood mononuclear cells of prostate cancer patients post-vaccination with a PSA-based vaccine, further indicating the immunogenicity of NGEP. These studies thus identify NGEP as a potential target for T cell-mediated immunotherapy of prostate cancer.     

Methylation-Associated Partial Down-Regulation of Mesothelin Causes Resistance to Anti-Mesothelin Immunotoxins in a Pancreatic Cancer Cell Line

Anti-mesothelin Pseudomonas exotoxin A-based recombinant immunotoxins (RITs) present a potential treatment modality for pancreatic ductal adenocarcinoma (PDAC). To study mechanisms of resistance, the sensitive PDAC cell line KLM-1 was intermittently exposed to the anti-mesothelin SS1-LR-GGS RIT. Surviving cells were resistant to various anti-mesothelin RITs (IC₅₀s >1 μg/ml), including the novel de-immunized RG7787. These resistant KLM-1-R cells were equally sensitive to the anti-CD71 HB21(Fv)-PE40 RIT as KLM-1, indicating resistance was specific to anti-mesothelin RITs. Mesothelin gene expression was partially down-regulated in KLM-1-R, resulting in 5-fold lower surface protein levels and decreased cellular uptake of RG7787 compared to KLM-1. Bisulfite sequencing analysis found that the mesothelin promoter region was significantly more methylated in KLM-1-R (59 ± 3.6%) compared to KLM-1 (41 ± 4.8%), indicating hypermethylation as a mechanism of mesothelin downregulation. The DNA methyltransferase inhibitor 5-azacytidine restored original mesothelin surface expression to more than half in KLM-1-R and increased sensitivity to RG7787 (IC₅₀ = 722.4 ± 232.6 ng/ml), although cells remained significantly less sensitive compared to parental KLM-1 cells (IC₅₀ = 4.41 ± 0.38 ng/ml). Mesothelin cDNA introduction in KLM-1-R led to 5-fold higher surface protein levels and significantly higher RG7887 uptake compared to KLM-1. As a result, the original sensitivity to RG7787 was fully restored (IC₅₀ = 4.49 ± 1.11 ng/ml). A significantly higher RG7787 uptake was thus required to reach the original cytotoxicity in resistant cells, hinting that intracellular RIT trafficking is also a limiting factor. RNA deep sequencing analysis of KLM-1 and KLM-1-R cells supported our experimental findings; compared to KLM-1, resistant cells displayed differential expression of genes linked to intracellular transport and an expression pattern that matched a more general hypermethylation status. In conclusion, resistance to anti-mesothelin RITs in KLM-1 is linked to a methylation-associated down-regulation of mesothelin, while aberrations in RIT trafficking could also play a role.     

Prostaglandin E1 binding and adenylate cyclase activation in normal and transformed fibroblasts

The binding of [³H]prostaglandin E₁ to membranes of clones of normal rat kidney fibroblasts (NRK cells) has been measured. Cell lines that responded to prostaglandin E₁, such as NRK and NRK transformed with Schmitt-Ruppin strain of Rous sarcoma virus (SR-NRK cells), have a high affinity prostaglandin E₁ binding site. Murine-sarcoma-virus-transformed lines of NRK cells are unresponsive to prostaglandin E₁ and have reduced prostaglandin E₁ binding. Exposure of cells to prostaglandin E₁ results both in decreases prostaglandin E₁ responsiveness and reduced prostaglandin E₁ binding.Activation of adenylate cyclase is correlated to binding of prostaglandin E₁ to receptors in both NRK and SR-NRK cell membranes. Mathematical models suggest that GTP decreases the affinity of hormone for its receptor while increasing the catalytic efficiency of adenylate cyclase, and that aggregates of occupied receptors may play an important role in the activation of adenylate cyclase.     

Phosphorylation of the solubilized insulin receptor by the gene product of the Rous sarcoma virus, pp60src

Both the insulin receptor and the gene product of the Rous sarcoma virus, pp60src, are protein kinases which phosphorylate themselves and other proteins on tyrosine residues. Addition of the solubilized insulin receptor to purified pp60src increased the phosphorylation of the beta-subunit of the insulin receptor. Phosphorylation of the insulin receptor by pp60src occurred both in the absence and presence of insulin but did not alter the insulin dose response for autophosphorylation of the receptor. Increasing concentrations of pp60src increased the phosphorylation of the receptor and at high concentrations equaled the maximal effect produced by insulin. Our observations suggest a possible mechanism by which the metabolically regulated insulin receptor tyrosine kinase could be altered by other tyrosine kinases such as that associated with pp60src. Further studies will be required to determine if the insulin receptor is phosphorylated by pp60src in Rous sarcoma virus-infected cells.