Growth, metastasis, and expression of CCL2 and CCL5 by murine mammary carcinomas are dependent upon Myd88

Previously we reported that lipopolysaccharide (LPS) treatment of murine mammary carcinomas resulted in decreased growth of the tumors. Here we show the decreased growth following LPS treatment was mediated through effects downstream of TLR4 and Myd88. Perhaps more notably, simply reducing TLR4 or Myd88 levels was sufficient to slow tumor growth rates. Moreover, reduced levels of Myd88 correlated with a significant reduction in lung metastasis as well as decreased CCL2 and CCL5 expression. To determine whether inhibiting Myd88 function could also alter tumor growth and chemokine expression we used a Myd88 homodimerization inhibitory peptide. Indeed, inhibiting Myd88 function in four different murine mammary carcinomas as well as the human breast cancer cell line MDA-MB-231 led to decreased growth as well as CCL2 and CCL5 expression. These data imply that Myd88 is important for growth and metastasis of breast cancer, and expression of at least two proinflammatory chemokines.