CPEB1 regulates β‐catenin mRNA translation and cell migration in astrocytes

Abstract

A crucial step in directed cell migration is the recruitment of cytoskeletal regulatory and signaling proteins to the leading edge of the cell. One protein localized to the leading edge of a migrating astrocyte is β-catenin. Using an in vitro wound healing assay, we show the localization of β-catenin to the leading edge is dependent upon new protein synthesis at the time of wounding. We examined the mRNA encoding β-catenin for potential regulatory elements and identified a conserved cytoplasmic polyadenylation element in the 3′-untranslated region (UTR). We now show that the CPE-binding protein (CPEB1) is expressed in astrocytes and that translation of β-catenin mRNA is regulated by CPEB1. Further, expression of a mutant CPEB1 protein in astrocytes not only blocks β-catenin protein localization, it inhibits cell migration. These findings demonstrate a role for CPEB1-mediated protein synthesis in the localization of β-catenin protein to the leading edge of migrating astrocytes and in regulating directed cell motility.

CPEB1 Regulates the Expression of MTDH/AEG-1 and Glioblastoma Cell Migration

“…The CPE sequences used for the reporter were based on the b-catenin 3 0 -UTR, a well-characterized target of CPEB1 (3,7). Approximately, 250 nucleotides of the 900-nucleotide b-catenin, 3 0 -UTR was amplified from mouse cDNA as previously described (7).…”

“…However, we were interested in what was happening to the posttranscriptional mechanisms controlling mRNA translation in transformed cells, specifically glioblastomas. The mRNA-binding protein cytoplasmic polyadenylation element-binding protein 1 (CPEB1) is present in both neurons and astrocytes, where it regulates the transport and translation of a distinct set of mRNAs (1)(2)(3). CPEB1 binds to mRNAs that contain a cis-element in their 3 0 -untranslated region (UTR) called a cytoplasmic polyadenylation element (CPE; ref.…”

“…Once bound to the CPE, CPEB1 initially silences mRNA translation but can activate translation following phosphorylation (4,5). In astrocytes, CPEB1 is phosphorylated by Aurora kinase A and confirmed CPEB1 targets include b-catenin and cyclin B1 mRNA (3,6), both proteins and the kinase have been implicated in cancer. To determine a functional role for CPEB1 in glioblastoma, we used a mutant version of CPEB1 that maintains the ability to bind specific mRNA, but does not contain the phosphorylation site necessary for activation, thus inhibiting translation of bound mRNA.…”

“…The mutant CPEB1 protein we termed DN-CPEB1 (dominant negative-CPEB1) because it binds specifically to CPEB1 targets, blocking the endogenous CPEB1 from binding, and reduces the translation of bound mRNA (1,3,7). Our rationale for using this approach was predicated on our goal of turning off CPEB1-mediated mRNA translation.…”

“…In astrocytes, CPEB1 was first described as a regulator of b-catenin mRNA and DN-CPEB1 expression blocked cells from migrating in a traditional scratch assay in vitro (3). Left unanswered in that study was whether DN-CPEB1 expression blocked all movement or rather altered the cells ability to move in a directed or progressive manner.…”