Depletion of NBR1 in urothelial carcinoma cells enhances rapamycin-induced apoptosis through impaired autophagy and mitochondrial dysfunction

Myeong Joo Kim, Gwang Yong Hwang, Min Ji Cho, Byung Hoon Chi, Serkin Park, In Ho Chang, Young Mi Whang

Research output: Contribution to journalArticle

Abstract

Rapamycin is well-recognized in the clinical therapeutic intervention for patients with cancer by specifically targeting mammalian target of rapamycin (mTOR) kinase. Rapamycin regulates general autophagy to clear damaged cells. Previously, we identified increased expression of messenger RNA levels of NBR1 (the neighbor of BRCA1 gene; autophagy cargo receptor) in human urothelial cancer (URCa) cells, which were not exhibited in response to rapamycin treatment for cell growth inhibition. Autophagy plays an important role in cellular physiology and offers protection against chemotherapeutic agents as an adaptive response required for maintaining cellular energy. Here, we hypothesized that loss of NBR1 sensitizes human URCa cells to growth inhibition induced by rapamycin treatment, leading to interruption of protective autophagic activation. Also, the potential role of mitochondria in regulating autophagy was tested to clarify the mechanism by which rapamycin induces apoptosis in NBR1-knockdown URCa cells. NBR1-knockdown URCa cells exhibited enhanced sensitivity to rapamycin associated with the suppression of autophagosomal elongation and mitochondrial defects. Loss of NBR1 expression altered the cellular responses to rapamycin treatment, resulting in impaired ATP homeostasis and an increase in reactive oxygen species (ROS). Although rapamycin treatment-induced autophagy by adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in NBR1-knockdown cells, it did not process the conjugated form of LC3B-II after activation by unc-51 like autophagy-activating kinase 1 (ULK1). NBR1-knockdown URCa cells exhibited rather profound mitochondrial dysfunctions in response to rapamycin treatment as evidenced by Δψm collapse, ATP depletion, ROS accumulation, and apoptosis activation. Therefore, our findings provide a rationale for rapamycin treatment of NBR1-knockdown human urothelial cancer through the regulation of autophagy and mitochondrial dysfunction by regulating the AMPK/mTOR signaling pathway, indicating that NBR1 can be a potential therapeutic target of human urothelial cancer.

Original languageEnglish
Pages (from-to)19186-19201
Number of pages16
JournalJournal of cellular biochemistry
Volume120
Issue number11
DOIs
Publication statusPublished - 2019 Nov 1

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Autophagy
Sirolimus
Cells
Apoptosis
Carcinoma
Neoplasms
Chemical activation
Adenosine Monophosphate
Protein Kinases
Therapeutics
Reactive Oxygen Species
Phosphotransferases
Adenosine Triphosphate
BRCA1 Gene
Phosphorylation
Mitochondria
Physiology
Cell growth
Growth
Elongation

Keywords

  • AMPK
  • autophagy
  • bladder cancer
  • mitochondrial biogenesis
  • NBR1
  • rapamycin

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Depletion of NBR1 in urothelial carcinoma cells enhances rapamycin-induced apoptosis through impaired autophagy and mitochondrial dysfunction. / Kim, Myeong Joo; Hwang, Gwang Yong; Cho, Min Ji; Chi, Byung Hoon; Park, Serkin; Chang, In Ho; Whang, Young Mi.

In: Journal of cellular biochemistry, Vol. 120, No. 11, 01.11.2019, p. 19186-19201.

Research output: Contribution to journalArticle

Kim, Myeong Joo ; Hwang, Gwang Yong ; Cho, Min Ji ; Chi, Byung Hoon ; Park, Serkin ; Chang, In Ho ; Whang, Young Mi. / Depletion of NBR1 in urothelial carcinoma cells enhances rapamycin-induced apoptosis through impaired autophagy and mitochondrial dysfunction. In: Journal of cellular biochemistry. 2019 ; Vol. 120, No. 11. pp. 19186-19201.
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AB - Rapamycin is well-recognized in the clinical therapeutic intervention for patients with cancer by specifically targeting mammalian target of rapamycin (mTOR) kinase. Rapamycin regulates general autophagy to clear damaged cells. Previously, we identified increased expression of messenger RNA levels of NBR1 (the neighbor of BRCA1 gene; autophagy cargo receptor) in human urothelial cancer (URCa) cells, which were not exhibited in response to rapamycin treatment for cell growth inhibition. Autophagy plays an important role in cellular physiology and offers protection against chemotherapeutic agents as an adaptive response required for maintaining cellular energy. Here, we hypothesized that loss of NBR1 sensitizes human URCa cells to growth inhibition induced by rapamycin treatment, leading to interruption of protective autophagic activation. Also, the potential role of mitochondria in regulating autophagy was tested to clarify the mechanism by which rapamycin induces apoptosis in NBR1-knockdown URCa cells. NBR1-knockdown URCa cells exhibited enhanced sensitivity to rapamycin associated with the suppression of autophagosomal elongation and mitochondrial defects. Loss of NBR1 expression altered the cellular responses to rapamycin treatment, resulting in impaired ATP homeostasis and an increase in reactive oxygen species (ROS). Although rapamycin treatment-induced autophagy by adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in NBR1-knockdown cells, it did not process the conjugated form of LC3B-II after activation by unc-51 like autophagy-activating kinase 1 (ULK1). NBR1-knockdown URCa cells exhibited rather profound mitochondrial dysfunctions in response to rapamycin treatment as evidenced by Δψm collapse, ATP depletion, ROS accumulation, and apoptosis activation. Therefore, our findings provide a rationale for rapamycin treatment of NBR1-knockdown human urothelial cancer through the regulation of autophagy and mitochondrial dysfunction by regulating the AMPK/mTOR signaling pathway, indicating that NBR1 can be a potential therapeutic target of human urothelial cancer.

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