Prohibitins Are Required for Cancer Cell Proliferation and Adhesion

Claudia Sievers,Kathleen Gottschalk,Thomas Rudel,Gwendolyn Billig,Syed A Aziz

doi:10.1371/journal.pone.0012735

Claudia Sievers, Kathleen Gottschalk + Show 3 more

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https://doi.org/10.1371/journal.pone.0012735

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Abstract

Prohibitin 1 (PHB1) is a highly conserved protein that together with its homologue prohibitin 2 (PHB2) mainly localizes to the inner mitochondrial membrane. Although it was originally identified by its ability to inhibit G1/S progression in human fibroblasts, its role as tumor suppressor is debated. To determine the function of prohibitins in maintaining cell homeostasis, we generated cancer cell lines expressing prohibitin-directed shRNAs. We show that prohibitin proteins are necessary for the proliferation of cancer cells. Down-regulation of prohibitin expression drastically reduced the rate of cell division. Furthermore, mitochondrial morphology was not affected, but loss of prohibitins did lead to the degradation of the fusion protein OPA1 and, in certain cancer cell lines, to a reduced capability to exhibit anchorage-independent growth. These cancer cells also exhibited reduced adhesion to the extracellular matrix. Taken together, these observations suggest prohibitins play a crucial role in adhesion processes in the cell and thereby sustaining cancer cell propagation and survival.

Highlights

Prohibitins (PHB1 and prohibitin 2 (PHB2)) are highly homologous proteins that are conserved throughout evolution and ubiquitously expressed [1,2,3]
Selective loss of Prohibitin 1 (PHB1) depleted cells To date no consensus on the function of PHB1 has been reached; in breast cancer cells, PHB1 has been reported to act as a tumor suppressor [15,16], whereas in primary endothelial cells depletion of PHB1 resulted in reduced cell proliferation [26]
Since OPA1 degradation has been shown to lead to changes in cristae morphology [32], we investigated the cristae structure of mitochondria in cells depleted of prohibitins using Transmission Electron Microscopy (TEM)

Summary

Introduction

Prohibitins (PHB1 and PHB2) are highly homologous proteins that are conserved throughout evolution and ubiquitously expressed [1,2,3]. Studies to date have associated PHB1 with diverse roles in the maintenance of cellular homeostasis. Initial work suggested it functions as an inhibitor of DNA synthesis, a role which was later assigned to its 39UTR [9,10]. SiRNA-mediated silencing of PHB1 expression was found to increase breast cancer cell proliferation [16]. Despite these indications of a tumor suppressor activity, recent studies have demonstrated reduced cell proliferation upon loss of PHB1 expression in mouse embryonic fibroblasts and other primary cells; and the rescue of cell proliferation upon overexpression of mitochondrial-targeted PHB2 [17]

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