Cell lineage tracing links ERα loss in Erbb2-positive breast cancers to the arising of a highly aggressive breast cancer subtype

HER2-positive (HER2+) breast cancers (BrCs) contain approximately equal numbers of ERα+HER2+ and ERα−HER2+ cases. An enduring obstacle is the unclear cell lineage-related characteristics of these BrCs. Although ERα+HER2+ BrCs could lose ERα to become ERα−HER2+ BrCs, direct evidence is missing. To investigate ERα dependencies and their implications during BrC growth and metastasis, we generated ERαCreRFP-T mice that produce an RFP-marked ERα+ mammary gland epithelial cell (MGEC) lineage. RCAS virus-mediated expression of Erbb2, a rodent Her2 homolog, first produced comparable numbers of ERα+RFP+Erbb2+ and ERα−RFP−Erbb2+ MGECs. Early hyperplasia developed mostly from ERα+RFP+Erbb2+ cells and ERα−RFP−Erbb2+ cells in these lesions were rare. The subsequently developed ductal carcinomas in situ had 64% slow-proliferating ERα+RFP+Erbb2+ cells, 15% fast-proliferating ERα−RFP+Erbb2+ cells derived from ERα+RFP+Erbb2+ cells, and 20% fast-proliferating ERα−RFP−Erbb2+ cells. The advanced tumors had mostly ERα−RFP+Erbb2+ and ERα−RFP−Erbb2+ cells and only a very small population of ERα+RFP+Erbb2+ cells. In ERα−RFP+Erbb2+ cells, GATA3 and FoxA1 decreased expression and ERα promoter regions became methylated, consistent with the loss of ERα expression. Lung metastases consisted of mostly ERα−RFP+Erbb2+ cells, a few ERα−RFP−Erbb2+ cells, and no ERα+RFP+Erbb2+ cells. The high metastatic capacity of ERα−RFP+Erbb2+ cells was associated with ERK1/2 activation. These results show that the slow-proliferating, nonmetastatic ERα+RFP+Erbb2+ cells progressively lose ERα during tumorigenesis to become fast-proliferating, highly metastatic ERα−RFP+Erbb2+ cells. The ERα−Erbb2+ BrCs with an ERα+ origin are more aggressive than those ERα−Erbb2+ BrCs with an ERα− origin, and thus, they should be distinguished and treated differently in the future.

Acyl-CoA-binding protein (ACBP) localizes to the endoplasmic reticulum and Golgi in a ligand-dependent manner in mammalian cells

In the present study, we microinjected fluorescently labelled liver bovine ACBP (acyl-CoA-binding protein) [FACI-50 (fluorescent acyl-CoA indicator-50)] into HeLa and BMGE (bovine mammary gland epithelial) cell lines to characterize the localization and dynamics of ACBP in living cells. Results showed that ACBP targeted to the ER (endoplasmic reticulum) and Golgi in a ligand-binding-dependent manner. A variant Y28F/K32A-FACI-50, which is unable to bind acyl-CoA, did no longer show association with the ER and became segregated from the Golgi, as analysed by intensity correlation calculations. Depletion of fatty acids from cells by addition of FAFBSA (fatty-acid-free BSA) significantly decreased FACI-50 association with the Golgi, whereas fatty acid overloading increased Golgi association, strongly supporting that ACBP associates with the Golgi in a ligand-dependent manner. FRAP (fluorescence recovery after photobleaching) showed that the fatty-acid-induced targeting of FACI-50 to the Golgi resulted in a 5-fold reduction in FACI-50 mobility. We suggest that ACBP is targeted to the ER and Golgi in a ligand-binding-dependent manner in living cells and propose that ACBP may be involved in vesicular trafficking.