HIF-1 activation induces doxorubicin resistance in MCF7 3-D spheroids via P-glycoprotein expression: a potential model of the chemo-resistance of invasive micropapillary carcinoma of the breast

BACKGROUND: Invasive micropapillary carcinoma (IMPC) of the breast is a distinct and aggressive variant of luminal type B breast cancer that does not respond to neoadjuvant chemotherapy. It is characterized by small pseudopapillary clusters of cancer cells with inverted cell polarity. To investigate whether hypoxia-inducible factor-1 (HIF-1) activation may be related to the drug resistance described in this tumor, we used MCF7 cancer cells cultured as 3-D spheroids, which morphologically simulate IMPC cell clusters. METHODS: HIF-1 activation was measured by EMSA and ELISA in MCF7 3-D spheroids and MCF7 monolayers. Binding of HIF-1α to MDR-1 gene promoter and modulation of P-glycoprotein (Pgp) expression was evaluated by ChIP assay and FACS analysis, respectively. Intracellular doxorubicin retention was measured by spectrofluorimetric assay and drug cytotoxicity by annexin V-FITC measurement and caspase activity assay. RESULTS: In MCF7 3-D spheroids HIF-1 was activated and recruited to participate to the transcriptional activity of MDR-1 gene, coding for Pgp. In addition, Pgp expression on the surface of cells obtained from 3-D spheroids was increased. MCF7 3-D spheroids accumulate less doxorubicin and are less sensitive to its cytotoxic effects than MCF7 cells cultured as monolayer. Finally, HIF-1α inhibition either by incubating cells with 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (a widely used HIF-1α inhibitor) or by transfecting cells with specific siRNA for HIF-1α significantly decreased the expression of Pgp on the surface of cells and increased the intracellular doxorubicin accumulation in MCF7 3-D spheroids. CONCLUSIONS: MCF7 breast cancer cells cultured as 3-D spheroids are resistant to doxorubicin and this resistance is associated with an increased Pgp expression in the plasma membrane via activation of HIF-1. The same mechanism may be suggested for IMPC drug resistance

Tropomodulin1 is required for membrane skeleton organization and hexagonal geometry of fiber cells in the mouse lens

The spectrin–actin network is disrupted in Tmod1 mutants, disturbing fiber cell morphology, and disordering lens cell organization

Bcl-2 protein in normal, hyperplastic and neoplastic breast tissues. A metabolite of the putative stem-cell subpopulation of the mammary gland

This investigation, though initially designed to examine the possible influence of the Bcl-2 protein on the node-metastasizing capacity of breast carcinomas, was amplified to study the expression of this antiapoptotic protein in normal breast lobules and hyperplastic lesions. We examined paraffin sections of 508 breast carcinomas, stained for Bcl-2, estrogen (ER) and progesterone receptors (PgR) and epithelial membrane antigen, and occasionally for other antigens as well. Only a few cells showing a strong Bcl-2 positivity spotted the tubulo-lobular units of normal resting glands, whereas such cells were relatively numerous in atrophic lobules, and very scarce in the terminally differentiated lactating breast. Columnar and usual types of hyperplasia were exclusively, or almost exclusively, composed of Bcl-2(+), ER(+) and PgR(+) cells. The foci of carcinoma in situ and those of invasive carcinomas were respectively 83% and 66% positive for Bcl-2 in at least 25% of their cells. Even among the invasive carcinomas, Bcl-2(+) cases included 83% and 87% of the ER(+) and PgR(+) cases, respectively (p=0.0001). Though there was a statistically significant inverse relation between Bcl-2 and tumor grade (p=0.0001), no significant association was found between Bcl-2 and lymph node stage. In conclusion, we suggest that normal, hyperplastic and neoplastic breast epithelial cells expressing the anti-apoptotic protein Bcl- 2 are immature cells that ought to form part of the stemcell subpopulation, which is committed to the development and to the maintenance of the normal gland and which gives rise to hyperplastic and neoplastic disorders when its proliferation is deregulated. In ductal proliferative changes Bcl-2 assays may be useful for diagnostic but not for prognostic purposes