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theses

Malignant melanoma has a high incidence of mortality due to its resistance to chemotherapy and tendency to metastasize, and in the past 60 years has seen an increase in industrialized nations. HYPOTHESIS: We propose that activation of the aryl hydrocarbon receptor (AhR) by environmental chemicals contributes to melanoma invasion through enhancing expression and activity of the matrix metalloproteinases (MMPs). Further, we hypothesize that AhR interactions with other signaling pathways are critical for AhR-induced MMP expression in these cells. The AhR, originally identified as the receptor for the polycyclic aromatic hydrocarbon (PAH) family of environmental contaminants, is activated by endogenous and exogenous compounds, including: flavonoids, UV photoproducts of tryptophan, as well as some synthetic retinoids. We have previously shown that TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)-activation of the AhR results in increased expression and activity of MMPs -1, -2 and -9. MMPs are a family of zinc- and calcium-dependent proteinases that degrade extracellular matrix (ECM) substrates that are involved in melanoma progression and metastasis. In this thesis we show that maximal TCDD-induced MMP-1 activation in A2058 melanoma cells requires 3 cis-acting response elements in the distal portion of the MMP-1 promoter, the NFκB, CCAAT and MITF sites. These elements are known to be downstream targets of the Ras/Raf signaling pathway, and our data also show that Ras/Raf activation is critical for AhR-induced MMP-1, -2 and -9 expression. Our data further suggest that AhR-Ras/Raf interactions result in deregulation of ECM metabolism, through alterations in expression of MMPs and their endogenous inhibitors, TIMP-1/-2 (tissue inhibitor of metalloproteinases). Lastly we demonstrate crosstalk between Ras/Raf signaling and the AhR pathway, and show that loss of AhR results in a reduction in Ras/Raf-mediated phosphorylation of ERK. Crosstalk is also demonstrated by a reduction of AhR expression and activity observed following Ras/Raf inhibition. Interestingly, 60% of all melanomas contain an activating mutation, V600EBRAF, in the Ras/Raf pathway, suggesting that melanomas may be more sensitive to AhR-activation. These data demonstrate that AhR-activated expression of MMPs in A2058 melanoma cells requires Ras/Raf signaling and that these pathways are directly involved in the regulation of enzymes vital to melanoma progression.

Ph.D.

Includes bibliographical references (p. 123-133).

http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.17361

ETD_985

doi:10.7282/T3WH2QB8

ETD doctoral

The author owns the copyright to this work.

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