The results of this study provide evidence that HDAC6 expression could be regulated by HER2 and AKT1 in breast cancer. The regulation of Akt phosphorylation by HDAC6 has been reported. Therefore, it is possible that HER2 may activate PI3K/Akt activity through up regulation of HDAC6. Like COX protein inhibitor 2, HDAC6 could induce pleiotropic effects on tumorigenesis and tumor progression. It appears that both are key genes that mediate HER2 effects on tumor progression. Modulation of HER2 expression by cell culture condition and tumorigenesis Non adherent cells derived from CD44 CD24 R2N1d cells were found to lose the expression of HER2, HDAC and AKT simultaneously. Apparently, the non adherent cells are resistant to anoikis by a mechanism in the absence Inhibitors,Modulators,Libraries of Akt expression.

After replating and reattachment as adherent culture, these cells regained the expression of these 3 genes. We have carried out experiments to test the importance of the expression of these genes in tumor development. The comparative study Inhibitors,Modulators,Libraries showed that non adherent R2N1d cells formed tumors with HER2 expres sion but at lower frequency and with much longer latency period. The results reaffirm the important role of HER2 in tumor development and show that HER2 expression can be modulated by cell culture condition. We speculate that HER2 expression could be modu lated by changed in vivo condition following chemother apy and/or radiation treatment. The few remaining cancer stem cells under the changed environment may not express HER2 and remain non tumorigenic for a long time.

However, these cells could express HER2 Inhibitors,Modulators,Libraries and become tumorigenic in response to tissue or humoral change. This may be a mechanism for tumor dormancy and relapse. Overall, this study provides clear evidence Inhibitors,Modulators,Libraries that Inhibitors,Modulators,Libraries HER2 has the ability to induce fast growing invasive breast tumors of stem cell origin. Considering the key genes induced by HER2 and their biological effects, it appears that the up regulation of the expression of COX 2 and HDAC6, and the increase in CD44 CD24 cancer stem cell frequency may account for the potent tumorigenic function of HER2 in breast carcinogenesis. To counter these HER2 effects, future therapy of HER2 positive breast tumors may consider a strategy of using the com bination of anti HER2 antibodies with other drugs that target breast cancer selleckchem ARQ197 stem cells such as metfdormin, salinomycin and CXCR1 to eliminate breast cancer stem cells. Methods Development of R2d and R2N1d cells Previously, we have reported the development of immor tal, weakly tumorigenic and highly tumorigenic cell lines from a human breast epithelial cell type with stem cell charac teristics after successive SV40 large T antigen transfec tion, X ray irradiation and ectopic expression of C erbB2/neu oncogene.