Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Cancer Biology

First Advisor

Karin List

Abstract

MATRIPTASE MEDIATED c-MET SIGNALING IN CRITICAL FOR BREAST CANCER PROGRESSION

by

GINA ZORATTI

Historically proteases have been associated with tumor progression and metastasis through degradation of the basement membrane. However, in recent years these enzymes have also been shown to play key roles in the activation of growth factors and cytokines, thereby activating pro-oncogenic signaling pathways. Matriptase (MT-SP1, ST14) is an epithelia-specific pericellular protease which has received considerable attention in recent years spurred by the consistent dysregulation of the protease in human epithelial tumors including breast cancer. We have performed both functional and mechanistic studies of matriptase in breast cancer using parallel, complementary in vitro and in vivo genetic "loss-of-function" strategies. To determine the contribution of matriptase to breast cancer in vivo we used matriptase hypomorhic mice with very low matriptase expression in the mammary gland. When crossed into the mammary tumor virus (MMTV) Polyomavirus middle T (PymT) mouse genetic mammary tumor model, matriptase hypomorphic mice displayed a significant decrease in tumor burden.

The hepatocyte growth factor (HGF)/c-Met signaling pathway is dysregulated in breast cancer and has been causally linked to breast carcinogenesis. It has previously been shown that matriptase is an effective activator of the inactive pro-form of HGF. To investigate whether matriptase mediated pro-HGF activation and elicitation of the c-Met signaling pathway plays a critical role in breast cancer we isolated primary mammary carcinoma cells from conditional matriptase knock-out mice carrying the β-actin-Cre ERTM transgene. Upon brief exposure to tamoxifen, matriptase was efficiently genetically ablated allowing for comparative analysis of c-Met phosphorylation/activation in matriptase sufficient and deficient primary carcinoma cells. Addition of pro-HGF to matriptase sufficient cells resulted in robust activation of c-Met and the downstream targets Gab1 and Akt. In contrast, matriptase ablation led to a greatly reduced level of c-Met pathway activation. Parallel experiments using RNA silencing of matriptase in four different human breast cancer cell lines similarly demonstrated abrogation of c-Met signaling upon pro-HGF stimulation. This abrogation of the c-Met signaling pathway affects the breast cancer cells proliferation rate as well as their invasiveness as demonstrated in 3D culture.

Our results suggest that matriptase is critically involved in pro-HGF activation leading to downstream signaling and elicitation of mitogenic, migratory and invasive responses in breast cancer.

Download

Share

COinS