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

Alakananda Basu¹

¹Department of Microbiology, Immunology and Genetics, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.

International Journal of Molecular Sciences

|June 19, 2020

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.

Insights

Protein kinase C-ε (PKCε) promotes breast cancer cell survival by inhibiting apoptosis and inducing autophagy. Silencing PKCε reduced autophagy, while its overexpression activated mTORC1 and increased autophagy, highlighting PKCε

Area of Science:

Oncology
Cell Biology
Biochemistry

Background:

Protein kinase C-ε (PKCε) is an anti-apoptotic protein crucial for breast cancer progression.
The role of PKCε in regulating autophagy, a key survival mechanism, within breast cancer cells remains largely unexplored.

Purpose of the Study:

To investigate whether PKCε regulates autophagy in breast cancer cells.
To elucidate the mechanisms by which PKCε influences cell survival pathways, including apoptosis and autophagy.

Main Methods:

Silencing of PKCε using small interfering RNA (siRNA) in T47D breast cancer cells.
Overexpression of PKCε in MCF-7 breast cancer cells.
Assessment of autophagy markers (LC3-II, p62, autophagy puncta) and apoptosis.
Manipulation of mechanistic target of rapamycin (mTOR) complexes (mTORC1/mTORC2) and autophagy-related gene 5 (Atg5).

Main Results:

PKCε silencing inhibited both basal and starvation-induced autophagy, evidenced by decreased LC3-II and autophagy puncta, and increased p62.
PKCε overexpression activated mTORC1, increased autophagic markers (LC3-I, LC3-II, p62), and inhibited apoptosis.
Inhibition of autophagy by Atg5 knockdown restored apoptosis in PKCε-overexpressing cells, indicating autophagy's role in PKCε-mediated survival.

Conclusions:

PKCε promotes breast cancer cell survival by concurrently inhibiting apoptosis and inducing autophagy.
PKCε's regulation of autophagy involves the mTORC1 pathway.
Targeting PKCε or its downstream pathways may offer novel therapeutic strategies for breast cancer.

Read full analysis

Keywords:

PKCε Raptor Rictor apoptosis autophagy breast cancer mTORC1 mTORC2

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