Date of Award

1-1-2009

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Biomedical Sciences

Content Description

1 online resource (x, 144 pages) : illustrations (some color)

Dissertation/Thesis Chair

Douglas S Conkliin

Committee Members

Julio Aguirre-Ghiso, Steve Hanes, Bruce Herron, Paula McKeown-Longo

Keywords

Alternative Promoter, Breast Cancer, Bruton's Tyrosine Kinase, Protein Tyrosine Kinase, RNA interference, Survival Pathways, Protein-tyrosine kinase, Breast

Subject Categories

Cell Biology | Genetics | Molecular Biology

Abstract

The receptor protein tyrosine kinases (RPTKs) and the non- receptor protein tyrosine kinases (PTKs) are among the most commonly up-regulated genes found in all types of cancers. Although, a large body of data implicates a majority of tyrosine kinases (TKs) in cancer, few have been extensively evaluated for any potential therapeutic benefit in any of the many subtypes of breast cancer. We have used RNA interference (RNAi) to perform a large-scale loss-of-function analysis to facilitate the identification of individual factors necessary for the survival of an ErbB2 positive breast cancer cell line. We have found that 30% of the TKs screened contributed to the viability of the BT474 breast cancer cell line. Surprisingly, multiple members of the Tec family of cytoplasmic TKs and Eph family of receptor TKs were among the TKs that when knocked down caused the greatest decrease in cellular viability. Further analysis of one Tec family member, Bruton's tyrosine kinase (BTK), which has multiple roles in regulating the development of immune cells but is not expected to be present in breast cells, revealed that its inhibition using RNAi or pharmacological inhibitors causes apoptosis in BT474 breast cancer cells. Our results show that an alternative form of BTK, containing an amino-terminal extension, is expressed in several breast cancer cell lines at significantly higher levels than in normal breast cells. There is no significant difference in cellular growth rates, survival, or morphology detected in cells expressing one form of the BTK protein or the other, suggesting the two BTK isoforms are functionally equivalent. Our results suggest, rather that aberrant transcription of the BTK gene from an alternative promoter causes BTK to be expressed in breast carcinomas at higher levels compared to normal, matched breast cells. Furthermore, constitutive signaling through the RPTK and oncogene ErbB2 may enhance BTK activation leading to the amplification of PLC gamma 2 signaling in ErbB2 and BTK positive breast cancer cells. Therefore, BTK may represent a highly promising, additional target in which to treat ErbB2 positive breast carcinomas.

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