T-cadherin-mediated cell growth regulation involves G₂ phase arrest and requires p21^CIP1/WAF1 expression

Members of the cadherin family have been implicated as growth regulators in multiple tumor types. Based on recent studies from our laboratory implicating T-cadherin expression in mouse brain tumorigenesis, we examined the role of T-cadherin in astrocytoma growth regulation. In this report, we show that T-cadherin expression increased during primary astrocyte physiologic growth arrest in response to contact inhibition and serum starvation in vitro, suggesting a function for T-cadherin in astrocyte growth regulation. We further demonstrate that transient and stable reexpression of T-cadherin in deficient C6 glioma cell lines results in growth suppression. In addition, T-cadherin-expressing C6 cell lines demonstrated increased homophilic cell aggregation, increased cell attachment to fibronectin, and decreased cell motility. Cell cycle flow cytometry demonstrated that T-cadherin reexpression resulted in G₂ phase arrest, which was confirmed by mitotic index analysis. This growth arrest was p53 independent, as T-cadherin could still mediate growth suppression in p53^-/- mouse embryonic fibroblasts. T-cadherin-expressing C6 cell lines exhibited increased p21^CIP1/WAF1, but not p27^Kip1, expression. Lastly, T-cadherin-mediated growth arrest was dependent on p21^CIP1/WAF1 expression and was eliminated in p21^CIP1/WAF1-deficient fibroblasts. Collectively, these observations suggest a novel mechanism of growth regulation for T-cadherin involving p21^CIP1/WAF1 expression and G₂ arrest.