Differential expression of beta 1 integrins in nonneoplastic smooth and striated muscle cells and in tumors derived from these cells.

Integrins are a superfamily of transmembrane alpha beta heterodimers that play an important role in cell-matrix and cell-cell interactions by acting as receptors for extracellular matrix proteins and for cell adhesion molecules. Using monoclonal antibodies against beta 1, alpha 1 to alpha 6, and alpha v subunits, the in situ distribution pattern of beta 1 integrins was examined immunohistochemically in nonneoplastic smooth and striated muscle cells and in their tumors. Nonneoplastic smooth muscle cells were beta 1+, alpha 1+, alpha 3+, alpha v+ and, in diverse localizations, also alpha 5+ or even alpha 6+. The expression of the beta 1 chain was conserved in all leiomyomas and leiomyosarcomas. The distribution pattern of the alpha subunits by contrast underwent several changes during malignant transformation of smooth muscle cells. These alterations consisted in a neoexpression of alpha 2, alpha 4, and alpha 6 as well as in an abnormal abrogation of alpha 1 and alpha 3 in some leiomyosarcomas. Except for the absence of alpha 5 in the majority of epithelioid leiomyosarcomas, expression of the alpha 5 and alpha v subunits was mainly conserved. In addition, tumors with epithelioid differentiation differed from typical cases by the absence of alpha 1 and the simultaneous presence of alpha 4. Adult striated muscle cells were beta 1+ but alpha 1- to alpha 6- and alpha v-, whereas fetal striated muscle cells were not only beta 1+ but also alpha 3+/-, alpha 4+/-, alpha 5+ and alpha 6+. In all rhabdomyosarcomas the expression of beta 1 was retained. Furthermore, the majority of cases showed the expression of one or more alpha subunits most of which, ie, alpha 4, alpha 5, and alpha 6, were also found in fetal striated muscle cells. In conclusion, beta 1 integrins exhibited a differential expression pattern along the two lines of myogenic differentiation. This integrin profile underwent characteristic changes during malignant transformation. Nevertheless, the compiled distribution patterns of the alpha 1, alpha 3, and alpha v subunits allowed in most instances the discrimination between tumors of smooth (alpha 1+/alpha 3+/alpha v+) and striated muscle (alpha 1-/alpha 3-/alpha v-) differentiation.