While the distal segments of the renal tubule consistently exhibited strong cytoplasmic and nuclear immunolabeling, significantly weaker YAP expression was observed in the proximal tubules, the putative site of origin of ccRCC MG-132 cell line (Figure 2, A and B). In RCC tissue samples, we found nuclear up-regulation of YAP expression compared to the proximal tubules in the adjacent normal tissue in 20 of 31 cases (65%; P < .0001). Of note, YAP staining intensity was considerably more prominent at the tumor margins representing the invasive front, and in several patients that showed high expression levels of YAP, we observed single keratin-positive tumor cells invading

the surrounding lymphocyte rich stroma, suggesting a possible role of Hippo signaling in ccRCC tumor cell invasion in vivo ( Figure 2, C–G). We cannot report correlation of YAP positivity with tumor grade based on this small sample size, with 22 of 31 cases being histopathologically Selleck Buparlisib classified as grade 2. However, vascular invasion or lymph node metastases were reported for 9 of 30 cases, and of these, 7 exhibited marked YAP positivity. Immunohistochemistry revealed strong cytoplasmic SAV1 expression in normal tubular epithelial cells, but curiously immunolabeling

was lost in adjacent neoplastic cells in 16 of 31 cases. Moreover, weak or absent SAV1 expression was found to correlate with nuclear localization of YAP, whereas sustained SAV1 expression vice versa caused nuclear exclusion of YAP (P = .0091; see Table 1 and Figure 2, H–K). To further study the role of Hippo signaling in renal cell cancer and to evaluate its potential as a putative therapeutic target, three ccRCC cell lines with high basal YAP expression levels—A498, ACHN, and MZ1774—were Celecoxib picked and dysfunctional Hippo signaling and aberrant YAP activity were abrogated by shRNA-mediated knockdown. For each of the respective parental cell lines, at least two different shRNA sequences directed

against YAP (designated as “YAPshRNA#4” and “YAPshRNA#5”) were used and compared to untransduced as well as to mock-transduced mass clones to minimize the risk of unspecific, off-target effects. Consistent stable knockdown of endogenous YAP was confirmed by Western blot analysis (Figure 3A). In all of the three cell lines examined, YAP knockdown led to a significant time-dependent reduction of net cell growth compared to mock-transduced cells as determined using MTS assays (Figure 3B). Next, effects of YAP knockdown on in vitro cell migration was assessed by employing modified Boyden chamber assays. Of note, a marked reduction of ccRCC migration was observed in response to YAP knockdown in all three cell lines examined (P < .001; Figure 3C), in line with the observation of YAP being associated to an invasive phenotype in vivo, as already discussed above. All experiments were done in triplicates and repeated at least once.