Date of Award

12-2002

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Bruce E. Bejcek

Second Advisor

Dr. Alexander J. Enyedi

Third Advisor

Dr. Bart O. Williams

Fourth Advisor

Dr. Silvia Rossbach

Abstract

Platelet-derived growth factor (PDGF) is overexpressed in various cancer cells and the overexpression may be correlated with the prognosis of several types of cancers. Binding of PDGF to its receptors induces receptor dimerization and subsequent autophosphorylation of tyrosine residues in the receptor’s cytoplasmic domains. The phosphorylated tyrosine residues interact with the secondary signaling molecules to initiate signaling cascades that trigger cellular changes by affecting downstream effectors. In our recent publication, we have shown that a NF-icB mediates the transformation of mouse fibroblast cells overexpressing PDGF B chain. Though there is a significant correlation between PDGF stimulation and N F-kB activity, it is still unclear what secondary signaling molecules and downstream targets regulate NFkB activity in the cell. In the glioblastoma cell line U87-MG which is known to overexpress the PDGF B chain and the PDGF beta receptor, N F-kB activity is significantly increased. A dominant negative mutant of PDGF beta receptor missing five intracellular tyrosine residues, which is unable to activate multiple secondary signaling molecules significantly, decreased N F-kB activity when it was introduced into U87-MG cells. When one o f the five tyrosine residue is added back so that the negative PDGF beta receptor can only activate PI3-K pathway, NF-kB activity returned to the level that was normal for U87-MG the cells. In addition, treating U87-MG cells with chemical inhibitors of the phosphatidylinocitol 3 kinase (PI3-K) pathway resulted in the significant inhibition o f NF-kB activity in a dose dependent manner. The use of short interfering RNA (siRNA) against p i 10 kinase of PI3-K to suppress the expression of p i 10 kinase also resulted in the inhibition of PI3-K pathway activity and NF-kB activity. The study presented here demonstrates that the PI3-K pathway is one o f the pathways that controls NF-kB activity in U87-MG cells. Elucidating the exact signaling cascades that mediate NF-kB activity upon PDGF stimulation will unveil a significant mechanism of PDGF induced transformation, which may lead to the discovery of novel molecular targets to suppress tumors with high PDGF activity.

Comments

Fifth Advisor: Dr. John R. Geisler

Access Setting

Dissertation-Open Access

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