All ETDs from UAB

Advisory Committee Chair

Steven L Carroll

Advisory Committee Members

Bruce Korf

Robin Lorenz

Anne Theibert

Danny Welch

Document Type

Dissertation

Date of Award

2011

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Malignant peripheral nerve sheath tumors (MPNSTs) arising in patients with neurofibromatosis type I (NF1) are null for the tumor suppressor neurofibromin, a negative regulator of signaling from both classic Ras (H-Ras, N-Ras and K-Ras) and R-Ras (R-Ras, R-Ras2/TC21, M-Ras/R-Ras3) subfamily members. Treatment of these tumors with Ras-targeted agents such as farnesyltransferase inhibitors has proven unsuccessful, likely due to the inability of these agents to successfully target all of the Ras isoforms regulated by neurofibromin. Thus, determining which Ras isoforms are critical for MPNST pathogenesis would be of therapeutic value. In this dissertation, we first review the clinical manifestations of NF1 and then describe transgenic models developed to study NF1-related tumorigenesis in the peripheral nervous system. We then examine the role of the classic Ras and R-Ras subfamilies in MPNST proliferation, survival and migration. We show that a dominant negative (DN) H-Ras mutant, which can inhibit activation of all three classic Ras isoforms, inhibits MPNST proliferation and survival but not migration. In contrast, a dominant negative R-Ras mutant, which is thought to inhibit R-Ras and R-Ras2 activation, inhibits MPNST proliferation and migration but not survival. We then utilize a mass spectrometric phosphoproteomics approach to identify the mechanistic basis for the differential effects of DN H-Ras and DN R-Ras on MPNST cells. Finally, we attempt to determine whether shRNA-mediation ablation a single classic Ras isoform can recapitulate the effects of pan-inhibition of the classic Ras subfamily with DN H-Ras. We show that K-Ras ablation, but not N-Ras ablation, can reduce proliferation to a similar extent as DN H-Ras expression in at least one MPNST cell line. All together, this dissertation explains our current understanding of how neurofibromin loss promotes tumor formation in the peripheral nervous system and extends our knowledge about the contribution of neurofibromin-regulated Ras isoforms to this process.

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