Regulation of Autophagy by Protein Kinase C-ε in Breast Cancer Cells.

Alakananda Basu

doi:10.3390/ijms21124247

Abstract

Protein kinase C-ε (PKCε), an anti-apoptotic protein, plays critical roles in breast cancer development and progression. Although autophagy is an important survival mechanism, it is not known if PKCε regulates autophagy in breast cancer cells. We have shown that silencing of PKCε by siRNA inhibited basal and starvation-induced autophagy in T47D breast cancer cells as determined by the decrease in LC3-II, increase in p62, and decrease in autophagy puncta both in the presence and absence of bafilomycin A1. The mechanistic target of rapamycin (mTOR) associates with Raptor or Rictor to form complex-1 (mTORC1) or complex-2 (mTORC2), respectively. Knockdown of PKCε attenuated an increase in autophagy caused by the depletion of Raptor and Rictor. Overexpression of PKCε in MCF-7 cells caused activation of mTORC1 and an increase in LC3-I, LC3-II, and p62. The mTORC1 inhibitor rapamycin abolished the increase in LC3-I and p62. Knockdown of mTOR and Rictor or starvation enhanced autophagy in PKCε overexpressing cells. While overexpression of PKCε in MCF-7 cells inhibited apoptosis, it induced autophagy in response to tumor necrosis factor-α. However, inhibition of autophagy by Atg5 knockdown restored apoptosis in PKCε-overexpressing cells. Thus, PKCε promotes breast cancer cell survival not only by inhibiting apoptosis but also by inducing autophagy.

Highlights

Protein kinase C (PKC) is a family of serine/threonine protein kinases that play critical roles in signal transduction and cell regulation [1]
Since inhibition of mTOR complex 1 (mTORC1) rather than activation autophagy, we examined the effect of the mTORC1 inhibitor rapamycin on the Protein kinase C-ε (PKCε)-mediated of mTORC1 is associated with an increase in autophagy, we examined the effect of the mTORC1 increase in LC3-I and LC3-II
Since rapamycin is a pharmacological inhibitor, suggesting that activation of mTORC1 by PKCε may be responsible for the increase in LC3-I and we examined how silencing of mechanistic target of rapamycin (mTOR) as well as the mTORC1 and mTOR complex 2 (mTORC2) components Raptor and p62

Summary

Introduction

Protein kinase C (PKC) is a family of serine/threonine protein kinases that play critical roles in signal transduction and cell regulation [1]. Based on the structural variations and biochemical properties, the PKC family can be categorized into three groups: Conventional (α, βI, βII, and γ), novel (δ, ε, η, and θ), and atypical (λ/ι and ξ) [2]. PKCε, a member of the novel PKC family, was identified as a transforming oncogene [3]. It is overexpressed in several cancers, including breast cancer, and has been associated with cancer development and progression [4,5,6].

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