All ETDs from UAB

Advisory Committee Chair

Yi-Ping Li

Advisory Committee Members

Robin D Hatton

Ralph D Sanderson

John D Mountz

Document Type

Dissertation

Date of Award

2016

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

It is known that the vacuolar ATPase has a number of functions related to tumor growth and progression such as involvement in drug resistance, pH regulation, autophagy, and lysosomal acid protease activation, as well as invasion and metastasis. Here we specifically describe the role of ATP6v1c1 in murine and human models of breast cancer. ATP6v1c1 is the dominant isoform of the coordinating subunit (ATP6v1c) involved in the assembly of the vacuolar ATPase complex which plays a key role in cancer growth and progression. We also describe how ATP6v1c1 knockdown impairs tumor nutrient signaling through mTORC1 and tumor cell proliferation, by inhibiting the normal recruitment of mTOR by the Ragulator complex to (LAMP-1+) lysosomes. The mTORC1 kinase regulatory complex promotes cancer growth by mediating growth factor signaling and nutrient availability. Its activity is often dysregulated in cancers, and especially breast cancer where it is expressed in preference to ATP6v1c2. Previous research has shown that amino acid sufficiency is detected by mTORC1, often generated by autophagy, through a mechanism requiring mTOR recruitment to mTORC1 through a signaling interaction between V-ATPase and the Ragulator complex. The mechanism underlying V-ATPase activation of mTORC1 in transformed cells and tumors is not totally clear and it was not previously known whether ATP6v1c1 was necessary for that activity. Our data reveal that silencing Atp6v1c1 in highly metastatic 4T1 mouse mammary tumor cells severely impairs 4T1 cell proliferation, migration, and invasion in vitro, as well as growth and metastasis in vivo. We also show that ATP6v1c1 knockdown inhibits mTORC1 pathway activation, and especially mTORC1 activation stimulated by amino acids. Furthermore, Atp6v1c1 knockdown reduced the proliferation of MCF-7, MDA-MB-435s, and MDA-MB-231 human breast cancer cells and inhibited their mTORC1 pathway activation, including its stimulation by amino acids. Unexpectedly, Atp6v1c1 knockdown in untransformed C3H10T1/2 cells had an effect on neither their growth nor mTORC1 pathway stimulation by amino acids. This work demonstrates a mechanism by which Atp6v1c1 enables cancer cell growth and metastasis through its dual functions in V-ATPase activation and mTOR pathway activation and shows that it may provide a novel therapeutic approach for breast cancer metastasis.

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