Cytokeratin 5 positive cells represent a steroid receptor negative and therapy resistant subpopulation in luminal breast cancers

Abstract

A majority of breast cancers are estrogen receptor (ER) positive and have a luminal epithelial phenotype. However, these ER+ tumors often contain heterogeneous subpopulations of ER− tumor cells. We previously identified a population of cytokeratin 5 (CK5) positive cells within ER+ and progesterone receptor positive (PR+) tumors that is both ER−PR− and CD44+, a marker of breast tumor-initiating cells (TICs). These CK5+ cells have properties of TICs in luminal tumor xenografts, and we speculated that they are more resistant to chemo- and anti-ER-targeted therapies than their ER+ neighbors. To test this, we used ER+PR+ T47D and MCF7 breast cancer cells. CK5+ cells had lower proliferative indices than CK5− cells, were less sensitive to 5-fluorouracil and docetaxel, and cultures became enriched for CK5+ cells after treatments. CK5+ cells were less prone to drug-induced apoptosis than CK5− cells. In cells treated with 17β-estradiol (E) plus anti-estrogens tamoxifen or fulvestrant, ER protein levels decreased, and CK5 protein levels increased, compared to controls treated with E alone. In ER+ tumors from patients treated with neoadjuvant endocrine therapies ER gene expression decreased, and CK5 gene expression increased in post compared to pre-treatment tumors. The number of CK5+ cells in tumors also increased in post- compared to pre-treatment tumors. We conclude that an ER−PR−CK5+ subpopulation found in many luminal tumors is resistant to standard endocrine and chemotherapies, relative to the majority ER+PR+CK5− cells. Compounds that effectively target these cells are needed to improve outcome in luminal breast cancers.

The role of steroid hormones in breast cancer stem cells

“…MCF7 mammospheres were also shown to be resistant to high doses of tamoxifen (Cariati et al 2008). Moreover, tamoxifen, fulvestrant, or estrogen deprivation increased the percentage of cells expressing cytokeratin 5 (CK5), a marker of human breast stem/progenitor cells also found in BCSCs, in T47D breast cancer cells (Creighton Kabos et al 2011). These data confirm that, while endocrine therapies target the differentiated proliferative breast cancer cells, they cannot effectively target the BCSCs.…”

“…In endocrine therapy, accumulating evidence suggests that there is an increase in BCSCs in ER C breast cancer following anti-estrogen treatment. Two studies have reported enrichment for cells with both BCSC gene and marker expression in breast tumor tissue following short term AI (letrozole) or tamoxifen treatment (Creighton et al 2010, Kabos et al 2011. Additionally, other studies demonstrated similar effects in ER C breast cancer cell lines.…”

Maintenance of hormone responsiveness in luminal breast cancers by suppression of Notch

“…These cells, referred to here as "luminobasal" cells, have tumorinitiating potential. Similar cells are up-regulated in patients whose luminal tumors develop resistance to chemo-and hormone therapies (13).…”

Cytokeratin 5 positive cells represent a therapy resistant subpopulation in epithelial ovarian cancer

“…We observed a histologic preference with half of serous and endometrioid carcinomas containing CK5+ cells, while in mucinous and non epithelial subtypes CK5 expression was infrequent. In breast cancer, ~50% of luminal ER+ tumors contain subpopulations of CK5+ cells where they show heightened endocrine and chemotherapy resistance (19). CK5 is expressed ubiquitously in basal-like breast cancer and is a signature marker of this subtype.…”

“…We have previously identified that half of ER+ breast tumors contain a subpopulation of cells that express the epithelial-specific intermediate filament cytokeratin 5 (CK5) (18,19), a marker of luminal progenitor and stem cells in the normal breast (20,21). CK5+ compared to intratumoral CK5− cells are relatively quiescent, tumor initiating, and have enhanced endocrine and chemotherapy resistance (18,19).…”