Schwann cells induce cancer cell dispersion and invasion.

Nerves enable cancer progression, as cancers have been shown to extend along nerves through the process of perineural invasion, which carries a poor prognosis. Furthermore, the innervation of some cancers promotes growth and metastases. It remains unclear, however, how nerves mechanistically contribute to cancer progression. Here, we demonstrated that Schwann cells promote cancer invasion through direct cancer cell contact. Histological evaluation of murine and human cancer specimens with perineural invasion uncovered a subpopulation of Schwann cells that associates with cancer cells. Coculture of cancer cells with dorsal root ganglion extracts revealed that Schwann cells direct cancer cells to migrate toward nerves and promote invasion in a contact-dependent manner. Upon contact, Schwann cells induced the formation of cancer cell protrusions in their direction and intercalated between the cancer cells, leading to cancer cell dispersion. The formation of these processes was dependent on Schwann cell expression of neural cell adhesion molecule 1 (NCAM1) and ultimately promoted perineural invasion. Moreover, NCAM1-deficient mice showed decreased neural invasion and less paralysis. Such Schwann cell behavior reflects normal Schwann cell programs that are typically activated in nerve repair but are instead exploited by cancer cells to promote perineural invasion and cancer progression.

The chemokine (CCL2-CCR2) signaling axis mediates perineural invasion.

UNLABELLED: Perineural invasion is a form of cancer progression where cancer cells invade along nerves. This behavior is associated with poor clinical outcomes; therefore, it is critical to identify novel ligand-receptor interactions between nerves and cancer cells that support the process of perineural invasion. A proteomic profiler chemokine array was used to screen for nerve-derived factors secreted from tissue explants of dorsal root ganglion (DRG), and CCL2 was identified as a lead candidate. Prostate cancer cell line expression of CCR2, the receptor to CCL2, correlated closely with MAPK and Akt pathway activity and cell migration towards CCL2 and DRG. In vitro nerve and cancer coculture invasion assays of perineural invasion demonstrated that cancer cell CCR2 expression facilitates perineural invasion. Perineural invasion is significantly diminished in coculture assays when using DRG harvested from CCL2(-/-) knockout mice as compared with control CCL2(+/+) mice, indicating that CCR2 is required for perineural invasion in this murine model of perineural invasion. Furthermore, 20 of 21 (95%) patient specimens of prostate adenocarcinoma with perineural invasion exhibited CCR2 expression by immunohistochemistry, while just 3 of 13 (23%) lacking perineural invasion expressed CCR2. In summary, nerve-released CCL2 supports prostate cancer migration and perineural invasion though CCR2-mediated signaling. IMPLICATIONS: These results reveal CCL2-CCR2 signaling as a key ligand-receptor mechanism that mediates cancer cell communication with nerves during perineural invasion and highlight a potential future therapeutic target.

GFRα1 released by nerves enhances cancer cell perineural invasion through GDNF-RET signaling.

The ability of cancer cells to invade along nerves is associated with aggressive disease and diminished patient survival rates. Perineural invasion (PNI) may be mediated by nerve secretion of glial cell line-derived neurotrophic factor (GDNF) attracting cancer cell migration through activation of cell surface Ret proto-oncogene (RET) receptors. GDNF family receptor (GFR)α1 acts as coreceptor with RET, with both required for response to GDNF. We demonstrate that GFRα1 released by nerves enhances PNI, even in the absence of cancer cell GFRα1 expression. Cancer cell migration toward GDNF, RET phosphorylation, and MAPK pathway activity are increased with exposure to soluble GFRα1 in a dose-dependent fashion. Dorsal root ganglia (DRG) release soluble GFRα1, which potentiates RET activation and cancer cell migration. In vitro DRG coculture assays of PNI show diminished PNI with DRG from GFRα1(+/-) mice compared with GFRα1(+/+) mice. An in vivo murine model of PNI demonstrates that cancer cells lacking GFRα1 maintain an ability to invade nerves and impair nerve function, whereas those lacking RET lose this ability. A tissue microarray of human pancreatic ductal adenocarcinomas demonstrates wide variance of cancer cell GFRα1 expression, suggesting an alternate source of GFRα1 in PNI. These findings collectively demonstrate that GFRα1 released by nerves enhances PNI through GDNF-RET signaling and that GFRα1 expression by cancer cells enhances but is not required for PNI. These results advance a mechanistic understanding of PNI and implicate the nerve itself as a key facilitator of this adverse cancer cell behavior.