BMC Cancer 2008, 8:270 http://www.biomedcentral.com/1471-2407/8/270 Interestingly, integrin β4 was not affected by the pheno- typic deviation and integrin α6 expression was signifi- cantly higher in the papillary tumors, mainly due to decreased expression in the carcinoma cells as compared to the wild-type mammary gland. This may imply that the difference in the tumor cells' motility, discussed further on, involves mainly the actin cytoskeleton. Caveolin (Cav)-1 and Cav-2 are principal structural com- ponents of the caveolar microdomain – a subcompart- ment of the plasma membrane [22]. Cav-1 has been reported to suppress cell transformation and its absence promotes early steps in mammary tumor formation in mice [22]. However, several lines of evidence have sug- gested that Cav-1 may have oncogenic properties leading to breast cancer [23-26]. Significantly (P < 0.05) higher levels of Cav-1 and Cav-2 expression were detected in the carcinoma tumors compared to their papillary adenocar- cinoma counterparts (2.8- and 3.8-fold, respectively). This difference resulted from an exclusive increase in Cav- 2 expression in the carcinoma tumors compared to the wild type mammary gland which was not found in the papillary adenocarcinomas. For Cav-1, higher levels of expression were detected in the wild type mammary gland compared to both types of tumors. Cav-1 expression has been reported to be confined to the myoepithelial cells of the mouse mammary gland [27]. Their absence in the papillary adenocarcinoma implies other targets for expression. Immunohistochemical and immunofluores- cence analyses confirmed Cav-1 expression in basal-like epithelial cells of the lactating gland and possibly in a few myoepithelial cells which are stained by both Cav-1 and smooth muscle actin (SMA) (Figure 6Aa,e,i). In the mul- tiparous gland, Cav-1 expression was augmented in the ductal epithelial cells (Figure 6Ab,f,j), as has also been observed in the breast tissue [26]. The carcinoma tumor sections were characterized by non-overlapping expres- sion of Cav-1 and SMA. Cav-1 was detected in the round red-stained epithelium-like cells, but not in the green- stained SMA ones (Figure. 6Ac,g,k). In contrast, in the papillary adenocarcinoma, Cav-1 staining was limited to fibroblasts and endothelial cells of the fibrovascular core (Figure 6Ad,h,l). Genes coding for cytoplasmic proteins that are down- stream of the integrins and implicated in cell adhesion and motility were generally also more highly expressed in the carcinoma tumors (Figure 5A). Among these encoded proteins are the Rho B and Rho C small GTPases and cal- pain 1, 3, and especially 6. The calpains are highly con- served intracellular, non-lysosomal, calcium-dependent proteases that prompt disassembly of focal-adhesion structures, leading to the turnover of the integrin-depend- ent cell-matrix adhesion needed for cell movement [28]. Interestingly, Cdc42 and its downstream N-WASP, which induces filopodia [29], were highly expressed in the pap- illary adenocarcinomas. The higher expression of actin in the carcinoma tumors is associated with the comparable expression profile of genes encoding cytoskeletal proteins. These genes are listed in Table 1 and include myosins, tropomyosins, tro- ponin and ADP-ribosylation factors. Genes encoding pro- teins that promote Ca++ sensitization such as troponin T1 (skeletal slow), calmodulin, cam kinase, caldemon and TNF were also highly expressed in the carcinomas. In con- trast, those promoting Ca++ desensitization, such as the MLCPs (Ppm1a, Ppm1g, Pp2r2d, Ppp2r1a, Ppp1 catalytic subunit and Cdc42), were more highly expressed in the papillary adenocarcinoma tumors. The Wingless-type (Wnt) pathway includes genes that are involved in transcription and cell adhesion (Figure 5B). The array analysis displayed a clear-cut differentiation in Wnt-related gene activation in the carcinoma vs. papillary adenocarcinoma tumors. Wnt5b and its Frizzled receptor Fzd8, which activate the non-canonical pathway, were more highly expressed in the papillary adenocarcinoma tumors. Higher expression of downstream Dishevelled-1 (Dvl-1) and JNK, which activate the PCP pathway and control cell movement, were also noted [30]. These changes were associated with higher expression of genes in the canonical pathway that encode proteins of the deg- radation complex. Those proteins target β-catenin to ubiq- uitination and proteolysis, rather than translocation into the nucleus. Thus, axin, PP2A and CKII were more highly expressed in the papillary adenocarcinoma, either due to enhanced expression compared to the wild-type mam- mary gland, or to downregulation of their expression in the carcinoma. One notable characteristic of the carcinoma tumors was high expression of Wnt2b and Fzd9, which cause distinct activation of the canonical pathway, leading to increased transcription [31]. The lower expression levels of the genes encoding the degradation complex in this pathway could allow better migration of β-catenin into the nucleus where it binds transcription factors, one of which is TCF. Indeed, TCF gene expression was significantly higher in the carcinoma than in the papillary adenocarcinoma tumors, while expression of TAK1, which blocks its nuclear localization and DNA binding [32], was higher in the papillary adenocarcinomas. Because the array data suggested differential expression of β-catenin in the subcellular compartments of the tumor cells, immunofluorescence analysis of β-catenin was per- formed (Figure 6B), and nuclei expressing β-catenin were quantitated in five microscopic fields (×40) from sections of five tumors of each type and three wild-type lactating Page 10 of 19 (page number not for citation purposes)