| Mitogen activated protein kinase (MAPK) signaling is frequently dysregulated in cancer and contributes to both tumor growth and metastasis. These signaling networks consist of a three-tiered phospho-relay system in which the upstream MAPK kinase kinase (MAP3Ks) control magnitude and duration of downstream MAPK activation. MAPK activation drives the subsequent physiological outcomes in the cell based on the location, strength and pattern of MAPK activation. While work to date has focused on activation and dysregulation of MAPK signaling in tumors, it has largely ignored the role of upstream MAP3Ks, despite the critical role of MAP3Ks in pathogenic MAPK signaling.;Herein, I use multiple screening methods to assess the role of MAP3Ks in MAPK network activation in vitro and physiological outcome in cancer in vivo. Specifically, I have devised an immunofluorescent based MAPK activation screen that I use to identify MAP3Ks that regulate MAPK network activation in response to seven stimuli. Screening identified novel positive and negative regulators of growth factor, cytokine and stress stimulated ERK1/2, JNK and p38 activation. In vivo, I use an orthotopic xenograft system with a library of shRNAs to nine MAP3Ks to screen for novel roles of MAP3Ks in tumor growth and metastasis. I identified new roles for six MAP3Ks in tumor growth and/or metastasis in vivo. Of these six MAP3Ks, I focus particularly on MEKK2 and MLK3 that control both tumor growth and metastasis in vivo. I demonstrate that MLK3 regulates cell growth and activation of JNK and p38 in vitro and controls macrophage recruitment to tumors in vivo. By contrast, I find MEKK2 regulates ERK5 activation by ERBB family members and I demonstrate that loss of ERK5 activation inhibits metastasis in vivo. Taken together, these results demonstrate the varied modes of MAP3K regulation of MAPK network activation and how altered MAPK signaling through MAP3Ks contributes to pathogenic signaling in cancer. |
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