LAMP2A overexpression in breast tumors promotes cancer cell survival via chaperone-mediated autophagy

Abstract

Lysosome-associated membrane protein type 2A (LAMP2A) is a key protein in the chaperone-mediated autophagy (CMA) pathway. LAMP2A helps in lysosomal uptake of modified and oxidatively damaged proteins directly into the lumen of lysosomes for degradation and protein turnover. Elevated expression of LAMP2A was observed in breast tumor tissues of all patients under investigation, suggesting a survival mechanism via CMA and LAMP2A. Reduced expression of the CMA substrates, GAPDH and PKM, was observed in most of the breast tumor tissues when compared with the normal adjacent tissues. Reactive oxygen species (ROS) mediated oxidative stress damages regulatory cellular components such as DNA, proteins and/or lipids. Protein carbonyl content (PCC) is widely used as a measure of total protein oxidation in cells. Ectopic expression of LAMP2A reduces PCC and thereby promotes cell survival during oxidative stress. Furthermore, inhibition of LAMP2A stimulates accumulation of GAPDH, AKT1 phosphorylation, generation of ROS, and induction of cellular apoptosis in breast cancer cells. Doxorubicin, which is a chemotherapeutic drug, often becomes ineffective against tumor cells with time due to chemotherapeutic resistance. Breast cancer cells deficient of LAMP2A demonstrate increased sensitivity to the drug. Thus, inhibiting CMA activity in breast tumor cells can be exploited as a potential therapeutic application in the treatment of breast cancer.

Keywords: :

• PCC
• TUNEL
• autophagy
• CMA
• tumor
• tissues
• doxorubicin

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

T.S. is grateful to the American Cancer Society (IRG #97-152-16-2) and the Fisher Center for Familial Cancer Center, Georgetown University, for financial support. T.S. would like to thank Prof. Eliot Rosen for laboratory space and Prof. Peter Shields, Prof. Stephen Byers, Dr. Michael Johnson and Prof. Robert Clark of Lombardi Cancer Center, Georgetown University and Dr. Melvin L. DePamphilis of NICHD, NIH for their continuing support. T.S. is grateful to Drs. Rabin Roy and Sujata Choudhury of Oncology, Lombardi Cancer Center, Georgetown University for helping out in activating the radioactive permit for pulse-chase experiment in their laboratory. Lastly T.S. would like to extend sincere thanks to Dr. Sushil Rane, principal investigator from NIDDK, NIH, who provided all the initial materials to execute the initial ideas. T.S. also acknowledges the support from microscopy and imaging shared resources, flow cytometry and cell sorting shared resources and tissue culture shared resource at Lombardi Comprehensive Cancer Center. T.S. thanks Dr. Asha Acharya, Dr. Vikas Rishi and Mrs. Jordan Woodrick for carefully editing this manuscript.

Supplemental Materials

Supplemental materials may be found here: www.landesbioscience.com/journals/autophagy/article/21654