Significance of alpha 9 beta 1 and alpha v beta 6 integrin expression in breast carcinoma

Both alpha 9 beta 1 and alpha v beta 6 integrins have been newly identified from the tracheal epithelium of guinea pig. It has been pointed out that alpha 9 beta 1 functions as a receptor for tenascin-C and osteopontin. As for the ligands of alpha v beta 6, fibronectin and tenascin-C have been identified. It has not been ascertained whether alpha 9 beta 1 and alpha v beta 6 are expressed in normal breast tissue, benign breast lesion or breast carcinoma.

Immunohistochemical staining for alpha 9 beta 1 and alpha v beta 6 was performed in benign breast lesion and breast carcinoma specimens. Western blotting was carried out on 11 breast carcinoma cases.

alpha 9 beta 1 was expressed in the cytoplasm of carcinoma cells in 23 of 90 cases (26%) and alpha v beta 6 in the membrane of carcinoma cells in 16 of 90 cases (18%). However, these findings of alpha 9 beta 1 and alpha v beta 6 did not correlate with any clinicopathological factors including the patients' age, tumor size, histological type of carcinoma, location of carcinoma cells and hormone receptor status. With regard to the histological grade of carcinoma, alpha v beta 6 and alpha 9 beta 1 expression did not statistically correlate, although no expression of alpha v beta 6 was observed in 14 cases of Grade I. On Western-blott analysis strong and weak bands consistent with alpha v beta 6 were noted in the membrane fraction extracted from breast carcinoma cells. On the other hand weak bands consistent with alpha 9 subunit were noted in the whole cell lysates of breast carcinoma cells and very weak or no bands consistent with alpha 9 subunit were noted in the membrane fraction extracted from the breast carcinoma cells.

Significance of alpha 9 beta 1 and alpha v beta 6 integrins expression in breast carcinoma was still unknown on clinicopathological examination. The findings of Western blot analysis may indicate that the transportation system of glycoproteins such as integrins to the cell membrane of carcinoma cells is disturbed, although these integrins can be produced.