Distribution of extracellular and cytoplasmic domains of the α3 and α6 integrin subunits in solid tumors

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Abstract
Integrins play an important role in malignant transformation and the invasion of tumors. They mediate cell‐cell and cell‐matrix interactions and participate in transduction of signals across the plasma membrane, processes dependent on the extracellular and cytoplasmic domains of integrins. We studied a selection of solid tumors by immunohistochemistry using monoclonal antibodies (MAbs) against the extracellular domain and the cytoplasmic variants (A and B) of the α3 and α6 integrin subunits. The tissue‐specific expression of ecto‐ and cyto‐domains of α3 and α6 is maintained in a subset of breast, colon, kidney and parotid tumors. In a few breast tumors, there was a switch in variant expression in that α6B was detected instead of α6A in normal breast tissue. In many colon and parotid tumors, one of the variants of α6 was missing, while both were detectable in the corresponding normal tissues. In contrast, co‐expression of the α6 variants was found in some kidney tumors, whereas only one of the variants was detected in the normal tissue. In a minority of colon and kidney tumors, the cytodomains of α3 and α6 were undetectable and total absence of α3 and α6 was noted in a subset of breast, colon, kidney and parotid tumors. These observations show that expression of the integrin variants in tumors varies considerably and support the concept that changes in expression may contribute to malignant behavior.