Metastasis persists as a significant unsolved hurdle in cancer treatment, with greater than 90% of cancer-related deaths attributed to metastasis. In order for cells to successfully metastasize, they must dynamically regulate cell adhesion. However, cell adhesion molecules are rarely mutated or deleted genetically in cancer, indicating that tumor cells are able to co-opt intrinsic regulatory mechanisms of adhesion to drive metastasis. We previously identified Activated Leukocyte Cell Adhesion Molecule (ALCAM) as a clinically relevant driver of metastasis and hypothesized that tunable regulation of its function contributes to tumor cell adhesion and metastasis. We tested this hypothesis through two channels.
We identified ALCAM as a novel binding partner of tetraspanin CD151, a known regulator of cell adhesion and motility. We previously demonstrated that clustering of integrin-free CD151 (CD151free) increased cell adhesion, decreased cell motility, and inhibited metastasis. Here, we identified ALCAM as a novel CD151 partner required for CD151free to control adhesion. Biochemical analyses revealed that CD151free is coupled to ALCAM by the scaffolding protein syntenin-1. Additionally, we show that the intracellular domain of ALCAM (ALCAM-ICD) is susceptible to ɣ-secretase cleavage, which releases a PDZ-binding peptide capable of disrupting the CD151/syntenin-1/ALCAM complex. Disruption of this complex impedes CD151free-mediated regulation of tumor cell adhesion and metastasis, demonstrating that CD151free controls tumor cell migration through a trimeric complex of CD151/syntenin-1/ALCAM.
Further evaluate of ALCAM revealed a potential alternative splicing which we predicted to control proteolytic shedding of its extracellular domain. We demonstrate that the loss of the membrane-proximal exon13 generates an ALCAM splice variant (ALCAM-Iso2) that enhances metastasis four-fold. Mechanistic studies identified a novel MMP14-dependent, membrane distal cleavage site in ALCAM-Iso2, which increases shedding ten-fold, thereby decreasing cellular cohesion and promoting motility. ALCAM-Iso2-expression was greatly increased in bladder cancer, further emphasizing that ALCAM alternative splicing can contribute to clinical disease progression. The requirement for both the loss of exon 13 and the gain of metalloprotease activity suggests that ALCAM shedding and concomitant regulation of dissemination is a locally tunable process.
In summary, this dissertation presents two mechanisms by which tumor cells are able to dynamically regulate cell adhesion to modulate migration and metastasis.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-03262018-125428 |
| Date | 27 March 2018 |
| Creators | Hebron, Katie Elizabeth |
| Contributors | Simon Hayward, Deborah Lannigan, Barbara Fingleton, Andries Zijlstra |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-03262018-125428/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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