Role of TRAF2/6 in tumour growth and bone metastases associated with breast cancer
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Date
02/07/2016Item status
Restricted AccessEmbargo end date
31/12/2100Author
Peramuhendige, Pushpabhani Prabha
Metadata
Abstract
Tumour necrosis factor receptor associated factors (TRAFs) play a key role in
signal transduction in mammalian cells. Several members of the TRAF family
have been identified but only TRAF2 and TRAF6 are implicated in the regulation
of both osteoclastic bone resorption and breast cancer. Here I studied the role of
TRAF2 and TRAF6 in breast cancer induced osteoclastogenesis and osteolysis. I
observed that TRAF2, but not TRAF6, is highly expressed in a highly metastatic
bone-tropic clone of the human MDA-MB-231-BT (MDA-231-BT) breast cancer
cells when compared to parental MDA-MB-231 (MDA-231) cells. Targeted
knockdown of TRAF2, but not TRAF6, in both parental MDA-231 and bone-tropic
MDA-231-BT breast cancer cells by siRNAs markedly reduced cell
migration and significantly reduced the ability of these cells and their conditioned
medium to induce osteoclast formation in RANKL stimulated bone marrow
cultures. Encouraged by these data, I generated stable parental MDA-231 and
bone-tropic MDA-231-BT breast cancer cell lines overexpressing TRAF2 using a
retroviral approach. Then, I went on to show that overexpression of TRAF2 in
parental MDA-231 cell line significantly stimulated directed cell migration and
3D invasion in vitro. Bone-tropic MDA-231-BT breast cancer cells over
expressing TRAF2 or their conditioned medium were significantly effective in
enhancing RANKL induced osteoclast formation in vitro. Mechanistic studies in
parental MDA-231 and bone-tropic MDA-231-BT breast cancer cells revealed
that over-expression of TRAF2 enhanced cell migration and osteoclastogenesis
via a mechanism that involves the activation of the breast cancer oncogene
IKKepsilon (IKKε) coupled with significant increase in levels of Vascular
endothelial growth factor (VEGF). Ex vivo studies in human MDA-231-mouse
calvaria organ co-cultures showed that conditioned medium obtained from MDA-
231 cells enhanced calvarial osteolysis. In vivo studies showed that
overexpression of TRAF2 in the human breast cancer cells MDA-231 enhanced
tumour incidence and tumour volume after orthotopic injection and exacerbated
osteolysis after supracalvarial injection of conditioned medium from these cells.
In conclusion, our studies showed that the TRAF2/IKK/VEGF axis in breast
cancer cells regulates breast cancer cell motility in vitro, osteoclastogenesis in
vitro and osteolysis ex vivo and in vivo. However, the role of TRAF2 in bone
metastasis associated with breast cancer will require further in vivo investigation.