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Access Type

WSU Access

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Cancer Biology

First Advisor

Raymond R. Mattingly

Abstract

Breast ductal carcinoma in situ (DCIS) is a non-obligate precursor of invasive ductal carcinoma (IDC). It is still unclear which DCIS will become invasive and which will remain indolent. Previous data by our group found that Sprouty4 transcript was differentially expressed between three DCIS cell lines and a non-transformed breast epithelial cell line. Sprouty proteins are important regulators of ERK/MAPK signaling, and have been studied in various cancers. We hypothesized that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling and that its loss/reduced expression is a mechanism by which DCIS lesions progress toward IDC, including triple-negative disease. Using immunohistochemistry we found that Sprouty4 expression was reduced in IDC patient samples compared to DCIS, and that ERK/MAPK phosphorylation had an inverse relationship to Sprouty4 expression. These observations were reproduced using a 3D culture model of disease progression. Knockdown of Sprouty4 in MCF10.DCIS cells increased ERK/MAPK phosphorylation as well as their invasive capability, and overexpression of Sprouty4 in MCF10.CA1d IDC cells reduced ERK/MAPK phosphorylation and the aggressive phenotype exhibited by these cells. Immunofluorescence experiments revealed dynamic changes in the actin cytoskeleton and data consistent with the relocation of E-cadherin back to the cell surface and the restoration of adherens junctions. To determine whether these effects were due to changes in ERK/MAPK signaling, MEK1/2 was pharmacologically inhibited in IDC cells. Nanomolar concentrations of drug restored an epithelial-like phenotype and reduced pericellular proteolysis, similar to Sprouty4 overexpression. From these data we conclude that Sprouty4 acts to control ERK/MAPK signaling in DCIS, thus limiting the progression of these premalignant breast lesions.

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