Different Expression Patterns of Somatostatin Receptor Subtypes in Cultured Epithelial Cells from Human Normal Prostate and Prostate Cancer1

Abstract

The transcripts of five SRIH receptor subtypes (SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5) were investigated by RT-PCR in epithelial cells (EC) and stromal cells (SC) from primary cultures of five normal human prostates and six prostate cancers. Primary cultures of prostate EC were established in serum-free keratynocyte medium with 5% FCS, epidermal growth factor, and bovine pituitary extract; SC were cultured in MEM with 10% FCS. Total RNA was extracted from EC and SC using a modified guanidine thiocyanate method. RT-PCR was performed after deoxyribonuclease treatment, using SSTR1-, SSTR2-, SSTR3-, SSTR4-, and SSTR5-specific-primers and adding glyceraldehyde-3-phosphate dehydrogenase-specific primers as internal control. A PCR product of the expected size of 334 bp, corresponding to SSTR1, was expressed only in EC from prostate cancer, whereas the expected 461-bp product of SSTR2 was found only in EC from normal prostate. SSTR3 messenger RNA was undetectable in normal and cancer EC, whereas SSTR4 and SSTR5 were present in both cell types. SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 messenger RNAs were not expressed in SC from both normal and cancer prostates. The RT-PCR method clearly demonstrated SSTRs' expression in the human prostate EC in vitro with differences between normal and tumoral samples. Our results may explain the ineffectiveness of some SSTR2 selective SRIH analogues in the treatment of prostate cancer and suggest that the absence of SSTR2 could represent a growth advantage in prostate cancer.

SST3-selective potent peptidic somatostatin receptor antagonists

“…However, the incidence and importance of sst 3 in human tumors is still a matter of debate. According to Virgolini et al (30), sst 3 is the most frequently expressed somatostatin receptor, including in exocrine pancreatic cancers; according to the majority of other authors (31)(32)(33)(34), it is relatively rarely expressed in tumors. Because most of these studies were performed by measuring sst 3 mRNA, it is evident that a confirmation of the presence or absence of the receptor protein, using sensitive receptor binding assays with selective radioligands such as 125 I-10, would be welcome, as no reports using sst 3 antibodies have conclusively answered this question.…”