Extracellular proteases in neoplastic development

L. M. Coussens, Ph.D.

Cancer Research Institute and Department of Pathology, University of California, San Francisco, CA,

AIM: To study dynamic changes occurring in the neoplastic microenvironment resulting from extracellular proteinase activation, we employ a transgenic mouse model of multi-stage squamous cell carcinoma (SCC) development where expression of human papillomavirus (HPV16) early region oncogenes (E6/E7) are targeted to skin keratinocytes by use of a human keratin 14 promoter/enhancer (K14), e.g., K14-HPV16 mice. HPV16 mice develop hyperplastic skin by one month of age with 100% penetrance. These broad neoplastic lesions progress into angiogenic dysplasias by six months of age, 50% of which undergo malignant conversion into metastatic SCCs [3]. Paralleling neoplastic progression of skin keratinocytes in HPV16 mice, extensive extracellular matrix (ECM) remodeling occurs in parallel with increased expression and activation of several members of the matrix metalloproteinase (MMP) family, e.g., MMP-2, -3, and -9. To functionally address the biologic role(s) of these MMPs, we have generated HPV16 mice harboring homozygous null mutations in each of the MMPs identified as potential modifiers of carcinogenesis. METHODS: To study the impact of individual MMPs on tumor progression, specific MMP-null mice are intercrossed with K14-HPV16 transgenic mice, and parameters of neoplastic development, e.g., epithelial proliferation, angiogenesis, inflammation, malignant conversion, monitored during de novo tumor progression. RESULTS: Analysis of HPV16 mice specifically lacking either MMP-2 or MMP9 suggest that these MMPs are important modifiers of HPV16-induced carcinogenesis. We found that MMP9 modifies epithelial carcinogenesis by increasing the rate and broadening the distribution of hyperproliferating oncogene-positive keratinocytes, regulates onset and intensity of angiogenesis, enhances malignant conversion of dysplasias into frank carcinomas, and effects differentiation characteristics of emergent tumors. Furthermore, we demonstrated that MMP9 imparts these regulatory capabilities on oncogene-positive neoplastic cells as a paracrine factor, originating from reactive inflammatory cells conscripted to support neoplastic growth and progression. CONCLUSIONS: Our goal over the next several years will be to define molecular mechanisms mediating the regulatory capabilities of MMPs by exploiting previously generated HPV16 and MMP-deficient colonies of mice. With this goal in mind, we are focusing on several key questions: 1) How do MMPs modulate epithelial proliferative responses, and, 2) What are the downstream targets (substrates) for MMP action that mediate these effects? Identification of these molecules will have ramifications for the development of new therapeutics that selectively block MMP-substrate interactions and/or selectively turn-off distinct MMP-activated signaling cascades. Our hope is that information gleaned from these combined approaches will lead to the development of more efficacious anti-cancer therapies.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Cancer Genomics.