14-3-3 zeta mediated epithelial -mesenchymal transition (EMT) contributes to ErbB2 overexpressing ductal carcinoma in situ (DCIS) progression into invasive breast cancer
ErbB2, is overexpressed in 20-30% of invasive/metastatic breast cancers, but is more frequently detected in an early stage, non-invasive breast cancer ductal carcinoma in situ (DCIS) (50-60%). It is still not clear how a sub-group of the ErbB2 overexpressing DCIS progress into invasive breast cancer. Our lab recently found that high levels of both ErhB2 and 14-3-3 zeta expression in breast cancer patients correlated with poor clinical outcome. More interestingly, our lab also found that co-overexpression of ErbB2 and 14-3-3 zeta in DCIS associated with recurrence of invasive disease. Therefore, I hypothesized that: ErbB2 and 14-3-3 zeta cooperatively drive DCIS progression into invasive breast cancer. I generated MCF10A cells overexpressing either ErbB2 alone or both ErbB2 and 14-3-3 zeta. ErbB2 overexpression in MCF-10A cells (grown in 3-dimensional matrigel culture) led to the disruption of acinar structures with no invasion, which mimics DCIS in vivo. Interestingly, co-overexpression of ErbB2 and 14-3-3 zeta in MCF10A cells led to further disrupted acinar structures formation, with strikingly invasive properties. I found that ErbB2 overexpression led to increased migration. 14-3-3 zeta overexpression led to epithelial-mesenchymal transition (EMT), with reduced expression of epithelial cell proteins, and de novo expression of mesenchymal cell proteins. Further studies demonstrated that loss of E-cadherin, the key event of EMT phenotype, was mediated by Smad interacting protein 1 (SIP-1) upregulation. SIP-1 is a zinc-finger transcriptional repressor that is regulated by TGFβ/Smads pathway. I found that 14-3-3 zeta interacted with TGFβ receptor I to stabilize it. The increased TGFβ receptor I led to the increased phospho-Smad3 levels in the nuclei of 10A.ErbB2.zeta cells, where it bound to SIP-1 promoter to upregulate SIP-1 expression. Indeed, inhibition of TGFβ/Smads pathway by its inhibitor led to a partial recovery of E-cadherin expression, which correlated with less invasive phenotype of 10A.ErbB2.zeta cells. Thus, ErbB2 overexpression contributed to the increased migration, while 14-3-3 zeta overexpression contributed to the decreased cell-cell adhesion via regulating EMT. Taken together, co-overexpression of ErbB2 and 14-3-3 zeta promoted invasion in MCF10A cells. Therefore, co-overexpression of ErbB2 and 14-3-3 zeta in DCIS patients may indicate a higher risk of progression into invasive breast cancer.
Lu, Jing, "14-3-3 zeta mediated epithelial -mesenchymal transition (EMT) contributes to ErbB2 overexpressing ductal carcinoma in situ (DCIS) progression into invasive breast cancer" (2008). Texas Medical Center Dissertations (via ProQuest). AAI3305166.