A mammosphere formation RNAi screen reveals that ATG4A promotes a breast cancer stem-like phenotype.
BACKGROUND
Breast cancer stem cells are suspected to be responsible for tumour recurrence, metastasis formation as well as chemoresistance. Consequently, great efforts have been made to understand the molecular mechanisms underlying cancer stem cell maintenance. In order to study these rare cells in-vitro, they are typically enriched via mammosphere culture. Here we developed a mammosphere-based negative selection shRNAi screening system suitable to analyse the involvement of thousands of genes in the survival of cells with cancer stem cell properties.


METHODS
We describe a sub-population expressing the stem-like marker CD44(+)/CD24(-/low) in SUM149 that were enriched in mammospheres. To identify genes functionally involved in the maintenance of the sub-population with cancer stem cell properties, we targeted over 5000 genes by RNAi and tested their ability to grow as mammospheres. The identified candidate ATG4A was validated in mammosphere and soft agar colony formation assays. Further, we evaluated the influence of ATG4A expression on the sub-population expressing the stem-like marker CD44(+)/CD24(low). Next, the tumorigenic potential of SUM149 after up- or down-regulation of ATG4A was examined by xenograft experiments.


RESULTS
Using this method, Jak-STAT as well as cytokine signalling were identified to be involved in mammosphere formation. Furthermore, the autophagy regulator ATG4A was found to be essential for the maintenance of a sub-population with cancer stem cell properties and to regulate breast cancer cell tumourigenicity in vivo.


CONCLUSIONS
In summary, we present a high-throughput screening system to identify genes involved in cancer stem cell maintenance and demonstrate its utility by means of ATG4A.
Jonas
J
Wolf
Dyah Laksmi
DL
Dewi
Johannes
J
Fredebohm
Karin
K
Müller-Decker
Christa
C
Flechtenmacher
Jörg D
JD
Hoheisel
Michael
M
Boettcher
D000818:Animals; D000071183:Autophagy-Related Proteins; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology*; D051927:CD24 Antigen / Q000378:metabolism; D018929:Cell Culture Techniques; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D057166:High-Throughput Screening Assays / Q000379:methods*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D016513:Mice, SCID; D014411:Neoplastic Stem Cells / Q000473:pathology*; D010085:Oxidative Phosphorylation; D010641:Phenotype; D034622:RNA Interference; D015203:Reproducibility of Results; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D000071183:Autophagy-Related Proteins; D051927:CD24 Antigen; C497889:CD24 protein, human; C497483:CD44 protein, human; D018960:Hyaluronan Receptors; C474025:ATG4A protein, human; D003546:Cysteine Endopeptidases