Sperm-associated antigen 1 is expressed early in pancreatic tumorigenesis and promotes motility of cancer cells

Sperm-associated antigen 1 (SPAG1) was recently identified in a rare form of infertility where anti-SPAG1 antibodies derived from the serum of an infertile woman were reported to cause sperm agglutination. Except for its expression and potential role in spermatogenesis, the function of SPAG1 is completely unknown. The unexpected finding of high levels of SPAG1 expression in pancreatic adenocarcinoma compared to normal pancreatic tissue in our previous cDNA array experiments prompted us to look in more detail at the expression and role of this gene in a panel of normal and malignant human tissues as well as in a larger series of pancreatic cancer specimens. We have generated an SPAG1-specific monoclonal antibody and showed high levels of SPAG1 protein in testis and in a large proportion of pancreatic ductal adenocarcinomas (PDAC). In the latter, SPAG1 expression was predominantly cytoplasmic and confined to malignant cells. Furthermore, the extent and intensity of SPAG1 expression was shown to be associated with stage and tumour nodal status, while analysis of precursor lesions, pancreatic intraepithelial neoplasias (PanINs), demonstrated its increased immunoreactivity with increasing PanIN grade, suggesting that SPAG1 is a novel marker of PDAC progression. Immunocytochemical analysis demonstrated colocalization of SPAG1 with microtubules, and their association was confirmed by co-immunoprecipitation; subsequent motility assays further substantiated a potential role of SPAG1 in cancer cell motility. Combined with the finding of its early expression in PDAC development, our data suggest that SPAG1 could contribute to the early spread and poor prognosis of pancreatic adenocarcinoma.