Marra et al. BMC Cancer 2010, 10:129 http://www.biomedcentral.com/1471-2407/10/129 Table 2 Genes differentially expressed upon reduction of PSCA expression and overlap between in vitro and in vivo dataset. Genes up regulated down regulated in vitro 123 119 in vivo 208 234 overlap 8 3 p-value 0.0001 0.19 implications of this observation remain to be elucidated [26]. The observed tumor specific expression of PSCA has prompted the development of therapeutic antibodies specific for this membrane protein. Indeed, growth inhi- bition has been observed upon antibody treatment of cells transfected with vectors expressing PSCA or of naturally expressing cell lines such as SW780. The pub- lished studies are in agreement with the data reported here indicating that reduced PSCA expression is asso- ciated with lower viability [7]. Thus, based on these published data, a better understanding of the biologic role played by PSCA in tumor growth is warranted. To shed light on PSCA role in tumor biology we com- pared PSCA expression in different cell lines and found expression on cell surface in few of them or in explanted primary tumors. Thus, the bladder cell line SW780 was engineered to obtain a pharmacological controlled expression of PSCA and to study the impact of reduced PSCA gene expression on cell viability and tumor growth. Here, we report a direct correlation between PSCA expression and tumor growth. Of note is the observation that pretreatment with dox in vitro Page 7 of 9 further reduced tumor growth. This latter result may be partially explained by the slow decay of PSCA displayed on the cell membrane as indicated by FACS analysis. A role for PSCA in tumor proliferation is further sup- ported by the biological pathway analysis of gene expres- sion profiling where a statistical significant association with “negative regulation of apoptosis” and “growth” was observed. Many of the pathways activated upon PSCA downregulation control key immune functions. Activation of IFNa/b signal transduction pathway was observed only in SW780-shPSCA tumors (Figure 2B) and it was not evident in tumors obtained upon injection of control cells. In contrast, similar studies conducted with these cell lines in vitro did not show induction of the pathway suggesting that in the tumor context additional factors such as those related to immune modulation may contri- bute to the observed microarray signature. A quantitative analysis of gene expression by qPCR confirmed overex- pression of IFNa/b genes (Figure 4). The activation of IFNa/b pathway only in vivo further supports the idea that triggering of this pathway is not determined by an intracellular mechanism related to double strand RNA, as it has been previously reported. On the contrary, the data suggest that IFNa/b activation is related to environmen- tal signals. The activation of IFNa/b pathway is consis- tent with a reduced tumor growth as previously shown with recombinant IFNa [27,28] . Nonetheless, further experiments are required to bet- ter characterize the link between PSCA downregulation and activation of immune pathways such as IFNa/b. In this direction it is worth mentioning a potential physical Figure 4 Expression levels of selected IFNa/b pathway genes as a function of PSCA expression. Expression levels for IFI27, IFI44L and IFIT1 genes were measured in individual SW780-shPSCA tumors (n = 6-8) (A) or in SW780-shPSCA in cell culture conditions (B) with or without dox treatment. Gene expression was measured by qPCR using the ΔΔ ct method. The average gene values in dox untreated mice served as reference and GAPDH gene as normalizer. In black average values in SW780-shPSCA tumors and in white SW780-shCont.