Downstream of mutant KRAS, the transcription regulator YAP is essential for neoplastic progression to pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with poor survival rates and frequently carries oncogenic KRAS mutation. However, KRAS has thus far not been a viable therapeutic target. We found that the abundance of YAP mRNA, which encodes Yes-associated protein (YAP), a protein regulated by the Hippo pathway during tissue development and homeostasis, was increased in human PDAC tissue compared with that in normal pancreatic epithelia. In genetically engineered Kras(G12D) and Kras(G12D):Trp53(R172H) mouse models, pancreas-specific deletion of Yap halted the progression of early neoplastic lesions to PDAC without affecting normal pancreatic development and endocrine function. Although Yap was dispensable for acinar to ductal metaplasia (ADM), an initial step in the progression to PDAC, Yap was critically required for the proliferation of mutant Kras or Kras:Trp53 neoplastic pancreatic ductal cells in culture and for their growth and progression to invasive PDAC in mice. Yap functioned as a critical transcriptional switch downstream of the oncogenic KRAS-mitogen-activated protein kinase (MAPK) pathway, promoting the expression of genes encoding secretory factors that cumulatively sustained neoplastic proliferation, a tumorigenic stromal response in the tumor microenvironment, and PDAC progression in Kras and Kras:Trp53 mutant pancreas tissue. Together, our findings identified Yap as a critical oncogenic KRAS effector and a promising therapeutic target for PDAC and possibly other types of KRAS-mutant cancers.

Abstract 1485: Snail activation of MAPK pathway may contributes to tumor insensitivity to tamoxifen chemotherapy in breast cancer cells

Snail is a zinc finger transcriptional repressor that induces epithelial-mesenchymal transitions (EMT) and is expressed at high levels in tumors. Snail contributes to chemotherapy resistance in ovarian, liver, colorectal, and breast carcinomas by activating the MAPK/ERK1/2 (ERK1/2) pathway .

ERK1/2 controls cell proliferation, survival, migration, and adhesion.

However, a role for MAPK in

Snail-mediated EMT in breast cancer is unclear. We hypothesized that Snail promotes EMT by decreasing cell adhesion and increasing cell migration through the MAPK pathway, resulting inresistance to Tamoxifen chemotherapy. Preliminary results suggest that breast cancer cells express variable levels of Snail that is higher than in normal MCF10A cells.

We utilized MCF-7 breast adenocarcinoma cells transfected stably with empty

Neo vector control (MCF-7 Neo) or constitutively active Snail cDNA (MCF-7

Snail). MCF-7 Neo and MCF-7 Snail have previously represented a breast cancer

EMT model; we used this model to examine cell adhesion and cell migration. We injected these cells into female nude mice to examine tumor size. We also examined activation of MAPK pathway using phospo-ERK (p-ERK) antibodies in response to Snail overexpression and the effect of inhibiting this pathway with

UO126 (MEK inhibitor, 20uM). Finally, we tested how Snail overexpression affects response to UO126 and/or Tamoxifen treatments using MTS cell proliferation assay. Our results showed that Snail overexpression led to decreased cell adhesion and increased cell migration on collagen and fibronectin in vitro, and increased tumorigenicity in vivo. Interestingly, immunofluorescent analysis revealed that activated ERK1/2 (p-ERK) had cytoplasmic localization in MCF-7 Neo, and exclusive nuclear localization in

MCF-7 Snail. Inhibition of activated ERK1/2 with UO126 antagonized cell adhesion primarily in MCF-7 Neo cells, while it decreased cell migration primarily in MCF-7 Snail cells. This would suggest that cytoplasmic p-ERK may be important for cell adhesion while nuclear p-ERK may be important for cell migration. MCF-7 Neo proliferation was consistently higher than MCF-7 Snail indicating that Snail may not play a significant role in cell proliferation, but other EMT functions like migration and adhesion. Tamoxifen treatment did not affect MCF-7 Snail cells morphologically, but led to sickly-appearing MCF-7

Neo cells. Additionally, MCF-7 Snail cells treated with Tamoxifen proliferated at similar rates to control untreated cells but co-treatment with UO126 greatly inhibited cell proliferation. This suggests that antagonizing nuclear p-ERK may sensitize breast cancer cells to Tamoxifen therapy. In conclusion, our study shows that Snail activation of MAPK pathway specifically within the nucleus promotes resistance to Tamoxifen and future ERK1/2 inhibition within the nucleus may sensitize cells to chemotherapy.

Citation Format: Bethany N. Smith, Peri Nagappan, Mahandranauth Chetram, LaTonia Taliaferro-Smith, Clayton Yates, Cimona Hinton, Valerie Odero-Marah. Snail activation of MAPK pathway may contributes to tumor insensitivity to tamoxifen chemotherapy in breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1485. doi:10.1158/1538-7445.AM2013-1485

Abstract 5747: Elucidating the mechanisms by which Snail transcription factor promotes resistance to chemotherapy in breast carcinomas

Snail (Snail1) is a zinc finger transcription factor that can induce EMT and is expressed at high levels in tumors. Maspin is a potential tumor suppressor, whose expression is lost as breast and prostate tumors progress during EMT. Maspin can be transcriptionally repressed by androgen receptor (AR) in prostate cancer cells. We hypothesized that overexpression of Snail will inhibit maspin expression and confer resistance to chemotherapy. Initially, we examined the expression of Snail and maspin in a panel of breast epithelial and breast cancer cells by RT-PCR and Western blot analysis. Preliminary results suggest that breast cancer cells express variable levels of Snail that is higher in breast cancer cells than in the normal MCF10A cells. We then utilized MCF-7 cells transfected stably with an empty Neo vector (MCF-7 Neo) or constitutively active Snail cDNA (MCF-7 Snail) that have been shown previously to represent an EMT model, and examined maspin, estrogen receptor alpha (ER-α) and AR levels by western blot analysis. MCF-7 Snail cells had upregulated levels of Snail and lower levels of maspin, ER-α and AR, as compared to MCF-7 Neo. MCF-7 Neo and MCF-7 Snail cells were also xenografted into nude mice and tissue sections stained immunohistochemically for Snail, maspin, and ER-α. Tumor volumes of MCF-7 Snail tumor xenografts were significantly larger than the MCF-7 Neo xenografts. MCF-7 Snail tissue sections expressed higher levels of Snail and lower levels of maspin and ER-α as compared to MCF-7 Neo sections. MCF-7 Neo and MCF-7 Snail cells were also treated with estradiol (E2, 0.01uM), tamoxifen (TAM, 10uM), and docetaxel (DOX, 1uM) individually; and in combination with E2 plus TAM and TAM plus DOX for periods of 24h and 72h to analyze changes in cell morphology and EMT marker expression. No effect on cell morphology or cell death was observed in MCF-7 Snail cells after TAM treatments, whereas TAM induced cell death in MCF-7 Neo. Expression of Snail was increased with E2 treatments and decreased with TAM, DOX, and combination treatments in MCF-7 Neo and MCF-7 Snail. AR expression decreased further in MCF-7 Snail cells and MCF-7 Neo following treatments with TAM and DOX. Overall, the Snail overexpression appears to promote resistance to TAM and DOX chemotherapeutic agents. The mechanism of Snail-regulated EMT needs to be investigated further to determine changes in breast cancer progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5747. doi:1538-7445.AM2012-5747