Evidence for a selective loss of somatostatin receptor subtype expression in male germ cell tumors of seminoma type

Somatostatin (SRIF) is a potent antiproliferative signal for both normal an d tumoral mammalian cells and an alteration in the SRIF receptor expression pattern has been associated with carcinogenesis. In the present study, the relevance of SRIF signaling to human male germ cell tumors was assessed at the receptor level. The expression of five SRIF receptor (sst1-sst5) mRNAs was estimated by RT-PCR and compared between normal and tumoral testes. Al l 12 normal testicular tissues studied contained sst3 and sst5 receptor tra nscripts whereas sst4 was present in almost all (11 of 12), sst1 transcript s mere consistently absent while the majority (11/12) of normal samples stu died did not contain sst2 mRNA, Parallel assessment of SRIF receptor mRNAs in 10 seminoma testicular germ cell tumors showed expression of a single re ceptor type, sst5, in all samples analyzed. All seminoma samples were deple ted in transcripts corresponding to sst1 and sst2 receptors while either ss t3 or sst4 mRNAs were absent in almost all (9 of 10) tumoral samples studie d, The comparison of SRIF receptor expression between normal tissue and sem inoma tumors thus points to a selective loss of sst3 and sst4 mRNA expressi on in seminomas, Altogether these data indicate that: (i) normal human test es are putative SRIF targets; (ii) loss of sst3 and sst4 SRIF receptor expr ession might be associated with seminoma carcinogenesis.