The Ability to Generate Senescent Progeny as a Mechanism Underlying Breast Cancer Cell Heterogeneity

Abstract

BackgroundBreast cancer is a remarkably heterogeneous disease. Luminal, basal-like, “normal-like”, and ERBB2+ subgroups were identified and were shown to have different prognoses. The mechanisms underlying this heterogeneity are poorly understood. In our study, we explored the role of cellular differentiation and senescence as a potential cause of heterogeneity.Methodology/Principal FindingsA panel of breast cancer cell lines, isogenic clones, and breast tumors were used. Based on their ability to generate senescent progeny under low-density clonogenic conditions, we classified breast cancer cell lines as senescent cell progenitor (SCP) and immortal cell progenitor (ICP) subtypes. All SCP cell lines expressed estrogen receptor (ER). Loss of ER expression combined with the accumulation of p21Cip1 correlated with senescence in these cell lines. p21Cip1 knockdown, estrogen-mediated ER activation or ectopic ER overexpression protected cells against senescence. In contrast, tamoxifen triggered a robust senescence response. As ER expression has been linked to luminal differentiation, we compared the differentiation status of SCP and ICP cell lines using stem/progenitor, luminal, and myoepithelial markers. The SCP cells produced CD24+ or ER+ luminal-like and ASMA+ myoepithelial-like progeny, in addition to CD44+ stem/progenitor-like cells. In contrast, ICP cell lines acted as differentiation-defective stem/progenitor cells. Some ICP cell lines generated only CD44+/CD24-/ER-/ASMA- progenitor/stem-like cells, and others also produced CD24+/ER- luminal-like, but not ASMA+ myoepithelial-like cells. Furthermore, gene expression profiles clustered SCP cell lines with luminal A and “normal-like” tumors, and ICP cell lines with luminal B and basal-like tumors. The ICP cells displayed higher tumorigenicity in immunodeficient mice.Conclusions/SignificanceLuminal A and “normal-like” breast cancer cell lines were able to generate luminal-like and myoepithelial-like progeny undergoing senescence arrest. In contrast, luminal B/basal-like cell lines acted as stem/progenitor cells with defective differentiation capacities. Our findings suggest that the malignancy of breast tumors is directly correlated with stem/progenitor phenotypes and poor differentiation potential.

Estrogen receptor alpha inhibits senescence-like phenotype and facilitates transformation induced by oncogenic ras in human mammary epithelial cells

“…It was reported that senescence in ERα-dependent breast cancer cells induced by tamoxifen appeared to result from the downregulation of survival signals generated by the transcriptional activity of ERα, indicating an anti-senescence role of ERα in breast cancer [8]. Consistently, our results demonstrated that the knockdown of ERα expression with the transfection of the siRNAs induced senescence-like phenotypes in ZR-75-1 and MCF-7 cells.…”

“…Cellular senescence is one of the mechanisms that normal cells use to avoid carcinogenesis [7]. It was demonstrated that tamoxifen can induce a senescent phenotype in several ERα+ breast cancer cells lines [8], which suggested that ERα might play an important role in the regulation of senescence and growth inhibition in breast cancer.…”

Novel anti-HER2 monoclonal antibodies: synergy and antagonism with tumor necrosis factor-α

“…Huh-7 cell line is used in lab since 1995 and was last tested for authenticity in 2010 (originally from Jack Wands Lab at Massachusetts General Hospital, Boston, MA). All breast cancer cell lines have been tested and authenticated by short tandem repeat profiling in September 2009 and February 2012, as described previously [25]. SK-BR-3 cells were grown in McCoy’s 5A medium.…”

“…SK-BR-3 cells were grown in McCoy’s 5A medium. MDA-MB-361, T47D, MCF-7, BT-474 and Huh-7 cells were grown in Dulbecco’s Modified Eagle Medium (DMEM), as described [25,26]. Hybridomas were grown in RPMI 1640, DMEM or Serum Free Media (SFM) from Hyclone (IL, USA).…”

Cancer Stem Cells in Drug Resistance and Drug Screening: Can We Exploit the Cancer Stem Cell Paradigm in Search for New Antitumor Agents?

“…Analysis of cell clones generated from single cells of breast carcinoma tumor cell lines in vitro showed that within 12 different cells lines tested there were two groups. One group (5 cell lines) produced senescent cells (positive for SA-β-Gal/negative for BrdU incorporation) with high frequency (5-40%) whereas the other group produced less that 5% of senescent cells (Mumcuoglu et al, 2010). Based on these features, the authors classified all breast cell lines studied as senescent cell progenitor (SCP) and immortal cell progenitor (ICP) cell subtypes.…”