Date of Award

1-1-2013

Embargo Period

1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology and Immunology

College

College of Graduate Studies

First Advisor

James S. Norris

Second Advisor

Xiang Liu

Third Advisor

Robin Muise-Helmericks

Fourth Advisor

Besim Ogretmen

Fifth Advisor

Christina Voelkel-Johnson

Abstract

Prostate cancer is a leading cause of cancer and cancer-related mortality in males in the United States. Acid ceramidase is frequently overexpressed in prostate cancer and catalyzes the deacylation of proapoptotic ceramide into sphingosine. Sphingosine is converted by sphingosine kinases into sphingosine 1-phosphate, which promotes numerous pro-cancer phenotypes. Due to the frequent overexpression of acid ceramidase in prostate cancer and its net cancer promoting signaling effects achieved by reducing ceramide and generating sphingosine 1-phosphate, the impact of acid ceramidase, and the lipid profiles it alters, on prostate cancer cell signaling were studied. Here we report the activation of the oncogeneic PI3K/Akt signaling pathway when acid ceramidase is overexpressed both in human prostate tissue and in prostate cancer cell lines. This effect was found to depend on sphingosine kinase 1; potentially reflecting increased accessibility of sphingosine kinase 1 to lysosome-derived sphingosine. Surprisingly, we found that S1P receptor 2 mediates acid ceramidase-induced Akt activation, which challenges the prevailing view in the literature that suggests predominately tumor suppressive functions for S1P receptor 2. Functionally, acid ceramidase overexpressing cells were found to be resistant to cytotoxic chemotherapies, but profoundly sensitive to inhibition of PI3K or Akt in proliferation assays and soft agar colony formation, suggesting acid ceramidase overexpressing cells become dependent on Akt signaling for their oncogenic phenotype. The tumor suppressor PTEN classically antagonizes PI3K-mediated activation of Akt, however emerging evidence suggests that nuclear PTEN is also critically important in suppressing cancer. Thus, mechanisms mediating nucleocytoplasmic shuttling of PTEN are of great interest. Following observations that acid ceramidase promoted net redistribution of PTEN from the nucleus into the cytoplasm, we found that the AC-induced Akt activation pathway described above also promoted nuclear egress of PTEN. Furthermore, we found that acid ceramidase and sphingosine 1-phosphate promote formation of a complex between Crm1 and PTEN, confirming that acid ceramidase promotes Crm1-mediated active export of PTEN. After investigating several potential mechanism including PTEN C-terminus phosphorylation and direct export through an in silico predicted PTEN nuclear export sequence, we found that acid ceramidase promotes PTEN nuclear export dependent upon Akt-mediated activation of S6K. Functionally, we found that acid ceramidase was able to promote resistance to Docetaxel chemotherapy, cell proliferation, and tumor formation in cells expressing wild type PTEN, but not in cells expressing nuclear localized PTEN, suggesting that acid ceramidase promotes prostate cancer in part through Akt-mediated nuclear export of PTEN.

Rights

All rights reserved. All rights reserved. Copyright is held by the author.

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