In a previous prospective study of 80 patients with squamous cell carcinoma of the upper aerodigestive tract, a progressive increase in expression of the integrin cell adhesion molecule α6β4 in suprabasilar cell layers of the tumor parenchyma was associated with an increase in early recurrence after therapy. In this study, we determined the relationship of the altered expression pattern of the integrin to changes occurring during benign, invasive, or metastatic stages of tumor development. Suprabasilar expression of integrin α6β4 appeared with neoplastic transformation in benign squamous papillomas, but homogeneous expression occurred more frequently in the parenchyma of primary and metastatic squamous cell carcinomas. The variation in the extent of suprabasilar integrin expression among the tumors corresponded to the variation in the population undergoing proliferation as determined by two independent markers of proliferation. Integrin expression was quantified in primary, HPV 16 DNA-immortalized, and v-ki-ras oncogene-transformed keratinocytes, and the pattern of expression was compared with cell cycle progression. Primary keratinocyte lines showed a bimodal distribution of integrin expression, with one population showing decreased integrin expression, cell size, and a block of cell cycle progression consistent with differentiation, whereas another population exhibited high integrin expression and full progression through the cell cycle, consistent with proliferation. HPV-immortalized and v-ki-ras-transformed cell lines undergoing continuous proliferation exhibited uniformly strong integrin expression, which was similar in intensity to that observed in the proliferating population of normal keratinocytes. Similar increases in expression of two additional integrins, α2β1 and α3β1, occurred along with integrin α6β4 in tissue specimens and cell lines derived from neoplasms. Thus, epidermal neoplasms display an increase in a population of cells exhibiting constitutive expression of a repertoire of integrins, which is similar to that found transiently in the acute phase of epidermal wound healing, a physiological response in which hyperproliferation, retention of multiple layers of proliferating cells, and migration occur. The association of a progressive increase in suprabasilar expression of these integrins with early tumor recurrence and advanced neoplasia suggests that constitutive expression and function of the same repertoire of integrins may be advantageous, rather than sufficient, for tumor progression.
Supported by NIH Intramural Project Z01-DC-00017.