Role of podoplanin expression in squamous cell carcinoma of upper aerodigestive tract.

Podoplanin, a type-1 transmembrane glycoprotein, was originally named due to its expression in renal podocytes of rats. It was subsequently detected in a variety of normal human tissues, including lymphatic endothelium. Although podoplanin has been identified as the endogenous ligand of C-type lectin-like receptor 2 (CLEC-2) on platelets, its physiological functions and pathways remain largely unknown. A role in lymphangiogenesis has been suggested, since podoplanin-deficient mice were found to die at birth with a phenotype of dilated, malfunctioning lymphatic vessels and lymphedema. Podoplanin is invariably expressed in some tumors, such as lymphangioma, seminoma and follicular dendritic cell tumor, but tumor cell expression of podoplanin is highly variable in squamous cell carcinoma (SCC). It has been found that high podoplanin expression is associated with lymph node metastasis and poor prognosis in SCC of the upper aerodigestive tract. Now there is growing evidence that podoplanin is also involved in carcinogenesis, cell motility, tumor invasiveness, platelet aggregation and hematogenous metastasis. Additionally, animal studies confirmed some in vivo effects of podoplanin-overexpressing tumors, including formation of more tumor lymphatic vessels, larger lymph node metastases, more platelet aggregation, and more pulmonary metastases. Several recently developed anti-podoplanin antibodies, such as NZ-1, P2-0 and hP2-0, have been shown to attenuate podoplanin-induced platelet aggregation and prevent experimental hematogenous metastasis in nude mice. These antibodies may be applied in preclinical and clinical studies to evaluate the possibility of podoplanin-targeted therapy.