TGFβ-dependent induction of interleukin-11 and interleukin-8 involves SMAD and p38 MAPK pathways in breast tumor models with varied bone metastases potential

We have delineated TGF beta signaling pathways in the production of osteolytic factors interleukin-8 and interleukin-11 in breast cancer cells with different bone metastases potential. Bone seeking MDA-MB-231(hm) cells expressed higher levels of IL-11, but lower levels of IL-8 compared to MDA-MB-231 cells. MCF-7 cells (mainly osteoblastic) did not express IL-8 or IL-11; MDA-MB-468 cells (weakly metastatic) expressed IL-8, but not IL-11. The upregulation of IL-11 and IL-8 was associated with the rapid activation of SMAD2/3 and p38 MAPK through the TGF beta/TGF beta R system. Analysis of TGF beta receptors indicated that MCF-7 cells do not express TGF beta RII, and MDA-MB-468 cells do not express SMAD4. Inactivation of SMAD4 or p38PMAPK gene via RNAi resulted in the inhibition of IL-11 and IL-8 production in MDA-MB-231(hm) cells; and overexpression of SMAD4 gene resulted in IL-11 production in MDA-MB-468 cells. TGF beta-1 induced SMAD3 translocation to the nuclei in MDA-MB-231, MDA-MB-231(hm) as well as in SMAD4 deficient MDA-MB-468, indicating that an alternate non-canonical pathway could be responsible for TGF beta-1 induced cytokine production in MDA-MB-468 cells. Thus, four breast cancer cell lines used in this study show differential expression and upregulation of the osteolytic factors in response to TGF beta-1 that involves both SMAD pathway, a non-canonical SMAD pathway, as well as p38 MAPK pathways.