ID: 33: CCL4 can promote bone metastasis of a murine breast cancer cell line, by interacting CCR5-expressing non-tumor cells in bone marrow

Abstract

From a murine breast cancer cell line, 4T1, we established a subclone, 4T1.3, which can metastasize to bone upon orthotopic injection into mammary fat pad. 4T1.3 cells proliferated in vitro and in vivo at the primarily injected site, mammary fat pad, with a similar growth rate as the parental cells. Moreover, 4T1.3 cells migrated to bone with a comparable speed as the parental cells, when injected intravenously. However, 4T1.3 cells survived better than the parental cells when injected directly into osseous tissues. 4T1.3 clone exhibited increased expression of cancer stem cell markers, CD44 and CD24, with upregulation of epithelial-mesenchymal transition (EMT) markers. Microarray analysis revealed an enhanced mRNA expression of chemokine, CCL4, by 4T1.3 clone. On the contrary, 4T1.3 clone did not express CCR5, a specific receptor for CCL4. CCL4 shRNA transfection had few effects on the expression of cancer stem cell markers and EMT markers, but reduced its tumorigenicity in bone when injected directly into osseous tissues. Moreover, tumor formation was attenuated in mice deficient in CCR5, compared with wild-type mice upon intra-osseous inoculation of 4T1.3. Thus, tumor cell-derived CCL4 can interact with CCR5-expressing non-tumor cells to gain a growth advantage in bone marrow.