Overexpression of angiomotin in sinonasal inverted papilloma

Abstract

Although inverted papilloma (IP) is one of the most common sinonasal tumors, its etiology and factors associated with tumor progression have not been fully determined. Generally, tumorigenesis or tumor growth requires angiogenesis to feed tumor cells. Angiomotin is a recently discovered protein that regulates migration and tubule formation in endothelial cells. It has been reported that angiomotin affects angiostatin (circulating inhibitor of angiogenesis), resulting in promotion of angiogenesis. Thus, we evaluated the expression and distribution of angiomotin in sinonasal IP, compared to normal control tissue. The study included 10 subjects with sinonasal IP and 5 normal controls. Ethmoid sinus mucosa obtained during reduction of blowout fractures was used as a normal control. Reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, immunohistochemistry, and Western blot analysis were used to assess the expression, intensity, and distribution of angiomotin in tissues. Positive bands for angiomotin were seen in all specimens by RT-PCR. The expression level of angiomotin was significantly upregulated in IP tissues versus normal sinus mucosa by real-time PCR. Immunohistochemistry revealed positive reactions on endothelial cells of capillaries and small vessels within the tumor and normal tissues, but the positivity was significantly stronger in IP. Western blot analysis showed that expression levels of angiomotin were increased in IP compared to normal sinus mucosa. Angiomotin, a novel protein in angiogenesis, was overexpressed in IP. Although it is not an etiological or initiating factor in tumor development, it seems to be associated with progression and growth of IP via promoting angiogenesis.