p120 reportedly is the first of the catenins to bind newly synthesized N-cadherin, and coprecipitates with the nascent precursor form of N-cadherin (Wahl et al., 2003). Because of the extraordinary efficiency of E-cadherin destruction after p120 knockdown, we first considered the possibility that p120 binding was necessary to stabilize E-cadherin during or after protein translation and before arrival at the cell surface. To examine E-cadherin synthesis in the absence of p120, we labeled the p120 knockdown A431 cells with [35S]methionine and performed pulse-chase experiments (Fig. 5 a). Interestingly, the rate of E-cadherin synthesis was unaffected by the absence of p120 (Fig. 5 a, compare top panels). Moreover, the processing and turnover of both the precursor and mature forms of E-cadherin were identical for at least 1 h after the pulse, after which the cadherin degradation curves diverged rapidly. Degradation of α- and β-catenins paralleled the loss of E-cadherin, as expected from the fact that these catenins are stabilized by cadherin binding.
