| Metastasis is a critical problem in the management of cancer patients. While improvements in systemic chemotherapies and surgical and radiation techniques are some of the greatest achievements of modern medicine, many advancements in cancer treatment cannot offer a cure in the setting of advanced disease. Therefore, understanding the molecular mechanisms underlying metastasis progression could have a valuable impact on the treatment of metastatic disease in the clinic. The mitogen-activated protein (MAP) kinase kinase MKK4 has been shown to suppress ovarian and prostate cancer metastasis. Previous studies showed that human ovarian cancer cells expressing MKK4 in experimental metastasis assays had decreased proliferation associated with induction of p21, suggesting that MKK4 regulates metastasis by inhibiting cell cycle progression. Expression of MKK6, a specific activator of the p38 MAP kinase, was also previously shown to suppress metastasis of ovarian cancer. Here, I report that inhibition of p38 did not significantly impact the number of metastases or animal survival. This may be due to functional redundancy of p38 isoforms. I also explore the mechanism of p21 induction in SKOV3ip.1 cells, and confirm that these cells do not express detectable p53 protein and harbor a mutation in Exon 4 of the TP53 gene. In response to doxorubicin-induced DNA damage, p21 induction and cell cycle arrest is observed in SKOV3ip.1 cells, and increased p38 phosphorylation is detected. Physical disruption also stimulated p38 phosphorylation, suggesting that MKK4 signaling may be activated by dissemination of cells during metastasis, leading to induction of cell cycle arrest. Finally, I report the results of a microarray experiment to identify transcriptional changes associated with metastasis suppression over the course of metastatic colonization. These studies identified that genes with reported roles in cytokinesis are significantly differentially expressed between MKK4- and empty vector-expressing cells at early time points during metastasis. The metastasis suppression signature was also predictive of disease progression in two publicly available datasets of clinical cancer, suggesting that studies of the mechanism of MKK4-mediated metastasis suppression may contribute to the understanding of the function of MKK4, but also provide insight into the molecular mechanisms underpinning clinical disease. |
