Author ORCID Identifier

https://orcid.org/0000-0003-4690-5115

Date of Graduation

8-2018

Document Type

Dissertation (PhD)

Program Affiliation

Neuroscience

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Andrew J. Bean, Ph.D.

Committee Member

Edgar T. Walters, Ph.D.

Committee Member

Shane R. Cunha, Ph.D.

Committee Member

Jack C. Waymire, Ph.D.

Committee Member

Peter E. Zage, M.D., Ph.D.

Abstract

Neuroblastoma is the most common malignancy in infants. Overexpression of the epidermal growth factor receptor (EGFR) in neuroblastoma tumors can result in enhanced EGFR signaling, uncontrolled proliferation, and may provide a mechanism for chemotherapy resistance. UBE4B, an E3/E4 ubiquitin ligase, ubiquitinates the EGFR and promotes its lysosomal degradation ultimately attenuating EGFR signaling. Interestingly, the UBE4B gene lies in a chromosomal region (1p36) whose loss is correlated with poor patient outcomes due to inefficient EGFR degradation and enhanced cell proliferation. We examined whether depletion of UBE4B in a chemoresistant neuroblastoma cell line would affect tumor responses to drugs that specifically target selected proteins that are upregulated in the absence of UBE4B. UBE4B depletion in a resistant neuroblastoma cell line resulted in a number of proteins whose levels were altered, including an increase in EGFR and STAT5a levels. We observed that treatment with Cetuximab, a therapeutic antibody targeting the EGFR, significantly inhibited the proliferation of neuroblastoma cells depleted of UBE4B. Addition of a STAT5 inhibitor potentiated the Cetuximab-induced inhibition of proliferation, reduced migration, and enhanced apoptosis in UBE4B-depleted neuroblastoma cells more than either drug treatment alone. Thus, screening resected patient tumors for 1p36 status and UBE4B levels may enable a novel treatment strategy in which selected patients who have low UBE4B-expressing tumors may benefit from simultaneously targeting multiple EGFR signaling pathways.

Keywords

Neuroblastoma, UBE4B, Cetuximab, STAT5, EGFR

Available for download on Tuesday, June 18, 2019

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