Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Toxicology and Cancer Biology

First Advisor

Dr. Isabel Mellon

Abstract

Hexavalent chromium (Cr(VI)) is classified as a confirmed human carcinogen by the International Agency for Research and Cancer (IARC) and by the U.S. Environmental Protection Agency (EPA). Chronic exposure to (Cr(VI)) causes malignant cell transformation in human bronchial epithelial BEAS-2B cells. These Cr(VI)-transformed cells exhibit a highly aggressive phenotype including increased migration, invasion, and angiogenesis. The Cas family protein neuronal precursor developmentally down regulated protein 9 (NEDD9/Cas-L/HEF1) was dramatically overexpressed in Cr(VI)-transformed cells compared to normal BEAS-2B cells. Knockdown of NEDD9 by its shRNA reduced migration and invasion in vitro measured by migration and invasion assays. shNEDD9 reduced tumor formation in nude mice injected subcutaneously and metastasis in mice injected in the lateral tail vein. NEDD9 is critical for the activation of c-Src kinase (Src) at Y416 and overexpression of focal adhesion kinase (FAK). These interactions with NEDD9, FAK, and Src indicate that NEDD9 was acting upstream from FAK and Src in Cr(VI)-transformed cells. NEDD9 expression or Src activation had downstream effects on migration and invasion. Interestingly β-Catenin activity was positively regulated by the expression of NEDD9 and the activation of Src. NEDD9 is critical for HIF-1α expression which leads to angiogenesis. The NEDD9 mediated angiogenic proteins VEGF, PECAM, ANG1, and MMP proteins are overexpressed in Cr(VI)-transformed cells. NEDD9 may increase angiogenesis by first mediating the phosphorylation of p38 and then HIF-1α. NEDD9 can also bind directly to CREB binding protein (CBP) a critical cofactor for HIF-1α transcriptional activity. These results lead us to believe that NEDD9 is a driving force in lung cancer aggressiveness by magnifying migration and invasion by facilitating FAK/Src binding and activation of Src kinase, by increasing β-Catenin activity and by increasing angiogenesis through HIF-1α stabilization and overexpression of downstream angiogenic proteins.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.041

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