Co-regulation and physical association of the 67-kDa monomeric laminin receptor and the alpha6beta4 integrin.

The interactions between tumor cells and laminin or other components of the extracellular matrix have been shown to play an important role in tumor invasion and metastasis. However, the role of the monomeric 67-kDa laminin receptor (67LR) remains unclear. We analyzed the regulation of 67LR expression under different culture conditions with respect to the expression of other well characterized laminin receptors. In A431 cells treated with laminin for different time periods, the regulation of 67LR expression correlated with expression of the alpha6 integrin subunit but not with the expression of other laminin receptors. Moreover, cytokine treatment resulted in down-modulated expression of the alpha6 integrin subunit and the 67LR. Co-regulation of the expression of the two receptors was further suggested by the observation that specific down-modulation of the alpha6-chain by antisense oligonucleotides was accompanied by a proportional decrease in the cell surface expression of 67LR. Biochemical analyses indicated co-immunoprecipitation of 67LR and the alpha6 subunit with an anti-alpha6 but not an anti-beta1 monoclonal antibody. Co-regulation of 67LR and alpha6 subunit expression, together with the physical association between the two receptors, supports the hypothesis that 67LR is an auxiliary molecule involved in regulating or stabilizing the interaction of laminin with the alpha6beta4 integrin.