Prostate targeting: PSP94 gene promoter/enhancer region directed prostate tissue-specific expression in a transgenic mouse prostate cancer model.

To date, only a few prostate-specific vector genes have been tested for prostate targeting in gene therapy of prostate cancer (CaP). Current clinical trials of gene therapy of CaP utilize the only two available vector genes with a combination of a rat probasin promoter and a human PSA promoter sequence in an adenovirus vector to target CaP. There is an urgent need to establish additional vector gene systems to sustain and propagate the current research. Since PSP94 (prostate secretory protein of 94 amino acids) is one of the three most abundant proteins secreted from the human prostate and is generally considered to be prostate tissue-specific in both human and rodents, we performed a transgenic experiment to assess the promoter/enhancer region of PSP94 gene-directed prostate targeting. Firstly, a series of progressive deletion mutants of a 3.84 kb PSP94 gene promoter/enhancer region (including parts of the intron 1 sequence) linked with a reporter LacZ gene was constructed and assessed in vitro in cell culture. Next, transgenic mice were generated with two transgene constructs using the SV40 early region (Tag oncogene) as a selection marker. PSP94 gene promoter/enhancer region-directed SV40 Tag expression specifically in the mouse was demonstrated in three breeding lines (A, B, C, n = 374) by immunohistochemistry staining of Tag expression. Specific targeting to the prostate in the PSP94 gene-directed transgenic CaP model was characterized histologically by correlation of SV40 Tag-induced tumorigenesis (tumor grading) with puberty and age (10-32 weeks). Prostatic hyperplasia was observed as early as 10 weeks of age, with subsequent emergence of prostatic intraepithelial neoplasia (PIN) and eventually high grade carcinoma in the prostate. The PSP94 transgenic mouse CaP model was further characterized by its tumor progression and metastatic tendency at 20 weeks of age and also by its responsiveness and refractoriness to androgen manipulation. This study indicates that the PSP94 gene promoter/enhancer has the potential for prostate specific targeting and may ultimately be of use in gene therapy of CaP.

Secretion of a soluble T cell promoting factor by the human prostate adenocarcinoma cell line DU-145.

INTRODUCTION: A variety of cancers suppress host immune defenses by secretion of soluble factors. Conditioned media (CM) from numerous cancer cell lines possess the ability to suppress proliferation of activated T cells. The effects of CM from the prostate cancer cell line DU-145 on T cell activation was investigated. MATERIALS AND METHODS: Human PBMC, purified T cells and Jurkat T cells were treated with DU-145 CM. Proliferation, cell cycle, apoptosis, Fas expression/and cytokine secretion were assessed by thymidine incorporation, flow cytometry and ELISA. RESULTS: DU-145 CM increased proliferation of concanavalin-A (ConA) activated peripheral blood mononuclear cells (PBMC) increasing the percentage of cells in the S/G2 phase of cell cycle. Treatment of the Jurkat T cell line with DU-145 CM induced a potent proliferative response. ConA-induced proliferation of purified T cells from human PBMC and murine splenocytes was augmented in a dose-dependent manner by addition of DU- 145 CM. DU- 145 CM treatment of ConA-activated T cells induced an increase in interleukin-2 (IL-2) production. The soluble factor(s) responsible for promoting T cell proliferation was dependent on protein synthesis by the DU- 145 cells and possessed a molecular weight greater than 10 kDa. CONCLUSION: DU- 145 cells secrete a soluble factor(s) > 10 kDa, whose production is dependent on protein synthesis and which acts as a promoter of T cell activation.

Rodent PSP94 gene expression is more specific to the dorsolateral prostate and less sensitive to androgen ablation than probasin.

To date, the rodent ventral prostate (VP) has been the focus of many studies on androgen action, less attention has been directed to the lateral prostate (LP) and the dorsal prostate (DP). The rodent VP has no clear homologous counterpart in the human prostate. The rodent LP and DP is the only prostate lobe comparable to the peripheral zone of the human prostate, where hormone-induced prostate cancer mainly occurs. To explore its utility for prostate targeting, we have studied the gene expression of PSP94 with rat probasin (rPB), a gene commonly used for prostate targeting in prostate cancer research and a gene typically responsive to androgen regulation. Firstly, we demonstrated PSP94 gene transcription being more specific to the LP and DP lobes than rPB, where rPB RNA was detected in the LP and DP and other lobes at different levels. Secondly, we found that PSP94 gene transcription decreased relatively slowly in response to androgen deprivation but recovered rapidly in response to testosterone replacement after complete ablation of PSP94 transcription. In the VP, gene transcripts of rPB were specifically responsive to androgen deprivation; however, they responded relatively slowly in the LP and DP. RNase protection experiments indicated that the slow response was not due to abnormal persistence of PSP94 messenger RNA specifically in the DP and LP lobes in comparison with rPB. Thirdly, Western blot analysis revealed that both PSP94 and rPB expression is specific to the LP and DP at the protein level, exhibiting slow responses to testosterone replacement after castration. We conclude that PSP94 gene expression at the transcriptional level is more specific to the LP and DP than rPB and thus less sensitive to androgen ablation. This may have clinical implications for strategies to target the prostate in cancer therapy.