Cytokeratin 5-Positive Cells Represent a Therapy Resistant subpopulation in Epithelial Ovarian Cancer.

OBJECTIVE: Cytokeratin 5 (CK5) is an epithelial cell marker implicated in stem and progenitor cell activity in glandular reproductive tissues and endocrine and chemotherapy resistance in estrogen receptor (ER)(+) breast cancer. The goal of this study was to determine the prevalence of CK5 expression in ovarian cancer and the response of CK5(+) cell populations to cisplatin therapy. MATERIALS AND METHODS: Cytokeratin 5 expression was evaluated in 2 ovarian tissue microarrays, representing 137 neoplasms, and 6 ovarian cancer cell lines. Cell lines were treated with IC(50) (half-maximal inhibitory concentration) cisplatin, and the prevalence of CK5(+) cells pretreatment and posttreatment was determined. Proliferation of CK5(+) versus CK5(-) cell populations was determined using 5-bromo-2'-deoxyuridine incorporation. Chemotherapy-induced apoptosis in CK5(+) versus CK5(-) cells was measured using immunohistochemical staining for cleaved caspase-3. RESULTS: Cytokeratin 5 was expressed in 39.3% (42 of 107) of epithelial ovarian cancers with a range of 1% to 80% positive cells. Serous and endometrioid histologic subtypes had the highest percentage of CK5(+) specimens. Cytokeratin 5 expression correlated with ER positivity (38 of 42 CK5(+) tumors were also ER(+)). Cytokeratin 5 was expressed in 5 of 6 overall and 4 of 4 ER(+) epithelial ovarian cancer cell lines ranging from 2.4% to 52.7% positive cells. Cytokeratin 5(+) compared with CK5(-) cells were slower proliferating. The prevalence of CK5(+) cells increased after 48-hour cisplatin treatment in 4 of 5 cell lines tested. Cytokeratin 5(+) ovarian cancer cells compared with CK5(-) ovarian cancer cells were more resistant to cisplatin-induced apoptosis. CONCLUSIONS: Cytokeratin 5 is expressed in a significant proportion of epithelial ovarian cancers and represents a slower proliferating chemoresistant subpopulation that may warrant cotargeting in combination therapy.

Progesterone-inducible cytokeratin 5-positive cells in luminal breast cancer exhibit progenitor properties.

Progestins play a deleterious role in the onset of breast cancer, yet their influence on existing breast cancer and tumor progression is not well understood. In luminal estrogen receptor (ER)- and progesterone receptor (PR)-positive breast cancer, progestins induce a fraction of cells to express cytokeratin 5 (CK5), a marker of basal epithelial and progenitor cells in the normal breast. CK5(+) cells lose expression of ER and PR and are relatively quiescent, increasing their resistance to endocrine and chemotherapy compared to intratumoral CK5(-)ER(+)PR(+) cells. Characterization of live CK5(+) cells has been hampered by a lack of means for their direct isolation. Here, we describe optical (GFP) and bioluminescent (luciferase) reporter models to quantitate and isolate CK5(+) cells in luminal breast cancer cell lines utilizing the human KRT5 gene promoter and a viral vector approach. Using this system, we confirmed that the induction of GFP(+)/CK5(+) cells is specific to progestins, is dependent on PR, can be blocked by antiprogestins, and does not occur with other steroid hormones. Progestin-induced, fluorescence-activated cell sorting-isolated CK5(+) cells had lower ER and PR mRNA, were slower cycling, and were relatively more invasive and sphere forming than their CK5(-) counterparts in vitro. Repeated progestin treatment and selection of GFP(+) cells enriched for a persistent population of CK5(+) cells, suggesting that this transition can be semi-permanent. These data support that in PR(+) breast cancers, progestins induce a subpopulation of CK5(+)ER(-)PR(-) cells with enhanced progenitor properties and have implications for treatment resistance and recurrence in luminal breast cancer.