The role of stem cell markers in multidrug resistance mediated by ABC transporters

Spheroid-induced heterogeneity and plasticity of uveal melanoma cells

PURPOSE

The mechanism underlying cancer heterogeneity and plasticity remains elusive, in spite of the fact that multiple hypotheses have been put forward. We intended to clarify this heterogeneity in uveal melanoma (UM) by looking for evidence of cancer stem cell involvement and a potential role of ZEB1 in cancer cell plasticity.

METHODS

Spheroids derived from human UM cells as well as xenograft tumors in nude mice were dissected for signs of heterogeneity and plasticity. Two human UM cell lines were studied: the epithelioid type C918 cell line and the spindle type OCM1 cell line. We knocked down ZEB1 in both cell lines to investigate its involvement in the regulation of stem-like cell formation and vascularization by qRT-PCR, immunohistochemistry, flow cytometry, electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assays.

RESULTS

We found that a small side population (SP) in OCM1 showed stem cell-like properties such as heterogeneity, remote dissemination and nuclear dye exclusion after spheroid formation in vitro. ZEB1 regulated UM stem cell generation indirectly by promoting cell proliferation to form large size tumors in vivo and spheroid in vitro, and directly by binding to stemness genes such as TERT and ABCB1. In addition, we found that ZEB1 participates in vasculogenic mimicry system formation through the regulation of CD34 and VE-cadherin expression.

CONCLUSIONS

From our data we conclude that cancer stem cells may contribute to UM heterogeneity and plasticity and that ZEB1 may play a regulatory role in it.

CD147 promotes MTX resistance by immune cells through up-regulating ABCG2 expression and function

BACKGROUND

Methotrexate (MTX) is a drug used to treat psoriasis due to inducing immune cell apoptosis. However, certain patients show MTX resistant. CD147, highly expressed by psoriatic PBMCs, is assumed to regulate MTX sensitivity. The underlining mechanism is still relatively understudied.

OBJECTIVE

To understand the mechanisms of that CD147 promotes MTX resistance in immune cells.

METHODS

The expression of CD147 and ABCG2 in PBMCs from psoriatic patients, cellular apoptosis and intracellular MTX amount were measured. We also checked the cellular drug sensitivity of CHO (Chinese Hamster Ovary) cell lines with introduced CD147 and Jurkat T cells depeleted CD147. By immunoprecipitation, we detected the interaction between CD147 and ABCG2.

RESULTS

Both ABCG2 and CD147 are highly expressed in psoriatic PBMCs. Cultured in vitro, the PBMCs from psoriatic patients were more resistant to MTX-induced apoptosis comparing to PBMCs from healthy people. Further studies demonstrated that exogenous overexpression of CD147 in CHO cells increased ABCG2 protein level. After MTX treatment, CD147 overexpressing CHO cells showed lower apoptosis rate and lower intracellular MTX concentration. On the contrary, knockdown of CD147 by shRNA in Jurkat T cells decreased ABCG2 expression, as well as increased MTX-induced apoptosis and decreased MTX efflux. Immunoprecipitation experiment revealed that the trans-membrane domain of CD147 conferred its' interaction with ABCG2.

CONCLUSION

Our study suggests a role of CD147 in regulating ABCG2 transportation of MTX in immune cells. Strategies involving targeting CD147 could be considered in clinical treatment of psoriatic patients resistant to MTX.