Autocrine Signaling of Neuropilin 1 Receptor Promotes Tumor Growth in Oral Squamous Cell Carcinoma

Introduction

Tumor angiogenesis is one of the hallmarks of oral squamous cell carcinoma (OSCC). Neuropilin 1 (NRP1) is a transmembrane receptor that binds angiogenic factors in the VEGF family in complex with VEGF recep- tor tyrosine kinases (RTKs) to stimulate the sprouting of blood vessels during neovascularization. Previously, our laboratory published that NRP1 is restricted to the suprabasal epithelium in normal oral mucosa, but is upregulated in the basal cell layer in dysplastic lesions. In OSCC, NRP1 expression was correlated with VEGF levels and tumor angiogenesis. NRP1 is not a kinase, therefore its role in epithelial or carcinoma cells which typically lack VEGF RTKs is unknown. Our aim is to determine the role that Nrp1 plays in OSCC tumorigenesis and explore the mechanistic action of NRP1 in carcinoma cells.

Methods/Results

To characterize the role of Nrp1 in keratinocytes during tu- morigenesis, K14-Cre^ERT;Nrp1-floxed (Nrp1-iKO) mice were treated with 4-Hydroxytamoxifen to induce Cre activity to delete the Nrp1 gene. Deletion in the epithelial compartment was confirmed using Nrp1 immunostaining on biop- sied tissues. Nrp1-iKO and control (K14-Cre) mice were given 4-NQO carcinogen in the drinking water, ad libitum, for 16 weeks to generate premalignant lesions and OSCC, then moved to regular drinking water for 9 weeks and then euthanized and necropsied. Results indicated fewer tumor incidence and smaller tumor size in the Nrp1-iKO group than in the control group. In vitro data confirmed a direct effect of VEGF on the growth of the human OSCC cell line (HSC3) in colony formation in soft agar, while silencing of NRP1 inhibited colony growth compared to con- trols.

Conclusion

Our data highlight the important role that NRP1 plays in OSCC and suggests that NRP1 signals in an autocrine fashion to enhance tumor growth in carcinoma cells.