MLK3 is critical for breast cancer cell migration and promotes a malignant phenotype in mammary epithelial cells

Abstract

The malignant phenotype in breast cancer is driven by aberrant signal transduction pathways. Mixed-lineage kinase-3 (MLK3) is a mammalian mitogen-activated protein kinase kinase kinase (MAP3K) that activates multiple MAPK pathways. Depending on the cellular context, MLK3 has been implicated in apoptosis, proliferation, migration and differentiation. Here we investigated the effect of MLK3 and its signaling to MAPKs in the acquisition of malignancy in breast cancer. We show that MLK3 is highly expressed in breast cancer cells. We provide evidence that MLK3's catalytic activity and signaling to c-jun N-terminal kinase (JNK) is required for migration of highly invasive breast cancer cells and for MLK3-induced migration of mammary epithelial cells. Expression of active MLK3 is sufficient to induce the invasion of mammary epithelial cells, which requires AP-1 activity and is accompanied by the expression of several proteins corresponding to AP-1-regulated invasion genes. To assess MLK3's contribution to the breast cancer malignant phenotype in a more physiological setting, we implemented a strategy to inducibly express active MLK3 in the preformed acini of MCF10A cells grown in 3D Matrigel. Induction of MLK3 expression dramatically increases acinar size and modestly perturbs apicobasal polarity. Remarkably, MLK3 expression induces luminal repopulation and suppresses the expression of the pro-apoptotic protein BimEL, as has been observed in Her2/Neu-expressing acini. Taken together, our data show that MLK3-JNK-AP-1 signaling is critical for breast cancer cell migration and invasion. Our current study uncovers both a proliferative and novel antiapoptotic role for MLK3 in the acquisition of a malignant phenotype in mammary epithelial cells. Thus, MLK3 may be an important therapeutic target for the treatment of invasive breast cancer.

Platelet MEKK3 regulates arterial thrombosis and myocardial infarct expansion in mice

“…33 Also, our recent studies demonstrated that Raf was responsible for platelet ERK5 activation. 34 MLK3 has been reported to activate JNKs and regulate apoptosis and dorsal closure during embryonic morphogenesis, 35,36 suggesting that MLK3 might play a synergistic role in MEKK3-mediated JNK2 activation in platelets. However, because the role of MLK3 in platelet activation is unclear, further studies are required.…”

MAP3K11 is a tumor suppressor targeted by the oncomiR miR-125b in early B cells

“…In mammary carcinoma, for example, miR-125b functions as a tumor suppressor, whereas MAP3K11 has been shown to regulate breast cancer cell migration and confers a malignant phenotype to mammary epithelial cells. 42,43 Thus, a part of the tumor-suppressive function of miR-125b in breast cancer may be mediated by MAP3K11 suppression, thereby controlling tumor cell metastasis and invasiveness. Indeed, such a relationship has recently been described in malignant melanoma, where loss of miR-125b expression promotes proliferation and invasion of cancer cells by upregulation of MAP3K11.…”

Mixed Lineage Kinase-c-Jun N-Terminal Kinase Axis: A Potential Therapeutic Target in Cancer

“…42 Corroborating MLK3's role in gastric cancer cell migration, it is reported that MLK3 plays a similar role in breast cancer cell migration via MLK3-JNK-AP-1 signaling. 7 Expression of active MLK3 was sufficient to induce mammary epithelial cell migration/invasion M Monographs via AP-1-regulated expression of genes involved in invasion. 7 Quite recently, Cronan et al 5 also identified MLK3 as one of the primary MAP3K members whose knockdown in the highly invasive breast cancer cell line MDA-MB-231 prevented tumor growth and metastasis.…”

“…7 Expression of active MLK3 was sufficient to induce mammary epithelial cell migration/invasion M Monographs via AP-1-regulated expression of genes involved in invasion. 7 Quite recently, Cronan et al 5 also identified MLK3 as one of the primary MAP3K members whose knockdown in the highly invasive breast cancer cell line MDA-MB-231 prevented tumor growth and metastasis. In this study, they also showed that loss of MLK3 expression increased mitotic infidelity and apoptosis in vitro.…”