Date of Award

Spring 4-28-2023

Embargo Period

5-23-2023

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biochemistry and Pathobiology

College

College of Graduate Studies

First Advisor

Steven Carroll

Second Advisor

Jody Longo

Abstract

Patients with Neurofibromatosis Type 1 have germline mutations in the neurofibromin gene (NF1) and are prone to develop tumors in the nervous system and elsewhere throughout their lifespan. Loss-of-function mutations of the remaining functional copy of the NF1 tumor suppressor gene in the Schwann cell lineage results in development of benign tumors known as dermal and plexiform neurofibromas. Mutations in additional tumor suppressor genes, like p53 and CDKN2A, subsequently transforms plexiform neurofibromas into highly aggressive malignant peripheral nerve sheath tumors (MPNSTs). At present, no effective treatments are available for MPNSTs, in fact some approaches make these tumors more aggressive. Since both neurofibromas and MPNSTs demonstrate Ras hyperactivation, many laboratories have targeted Ras and key downstream effectors of Ras. Unfortunately, all attempts to develop downstream targeted therapies for MPNSTs have failed. However, upstream receptor tyrosine kinases (RTKs) can activate Ras through several mechanisms in MPNSTs. One RTK, erbB3, has yet to be investigated in MPNST pathogenesis. Furthermore, upstream, and parallel Ras activation by intracellular calcium signaling has also been implicated in MPNSTs but has not yet been investigated. We found that erbB3 is expressed and required for the proliferation and survival of MPNST cells and that erbB3 promotes calcium-mediated signaling viii mechanisms. Using genome-wide shRNA screens, NRG1β-erbB3 microarray analyses and in vitro drug kinomics screening, we identified novel erbB3 and calcium regulated signaling pathways as potential druggable targets for MPNSTs. Due to the historical failure of monotherapy drug treatments in MPNST patients, we sought to identify a combinatorial treatment that effectively inhibited MPNST cell proliferation and survival by targeting upstream activators. We discovered that erbB3 signals through both canonical and novel pathways in MPNSTs and that calcium-calmodulin mediated signaling is an MPNST vulnerability. We have identified a novel calmodulin-independent regulation of the calmodulin effector calmodulin-regulated kinase II (CamKII) and have shown that simultaneous inhibition of erbB3 and calcium-calmodulin mediated signaling significantly reduces MPNST cell proliferation and survival. We conclude that erbB3 contributes significantly to MPNST growth and survival as well as calcium-calmodulin mediated signaling and that inhibition of both pathways is more effective than treatment with erbB or calmodulin inhibitors alone.

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Copyright is held by the author. All rights reserved.

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