Lysophosphatidic acid (LPA) induces actin rearrangement, focal adhesion assembly, and cell migration through the activation of small G protein Rho and its downstream effectors. These diverse cellular responses are mediated by its associated G protein-coupled receptors. However, the mechanisms and specificity by which these LPA receptors mediate LPA actions are still poorly understood. Here we show that LPA stimulation promotes the interaction of the LPA 2 receptor with a focal adhesion molecule, TRIP6 (thyroid receptor interacting protein 6)/ZRP-1 (zyxin-related protein 1). TRIP6 directly binds to the carboxyl-terminal tail of the LPA 2 receptor through its LIM domains. LPA-dependent recruitment of TRIP6 to the plasma membrane promotes its targeting to focal adhesions and co-localization with actin stress fibers. In addition, TRIP6 associates with the components of focal complexes including paxillin, focal adhesion kinase, c-Src, and p130 cas in an agonistdependent manner. Overexpression of TRIP6 augments LPA-induced cell migration; in contrast, suppression of endogenous TRIP6 expression by a TRIP6-specific small interfering RNA reduces it in SKOV3 ovarian cancer cells. Strikingly, the association with TRIP6 is specific to the LPA 2 receptor but not LPA 1 or LPA 3 receptor, indicating a specific role for TRIP6 in regulating LPA 2 receptor-mediated signaling. Taken together, our results suggest that TRIP6 functions at a point of convergence between the activated LPA 2 receptor and downstream signals involved in cell adhesion and migration.Lysophosphatidic acid (LPA) 1 is a bioactive growth factorlike phospholipid, which mediates diverse biological responses such as mitogenesis, differentiation, cell survival, angiogenesis, inflammation, and cell migration (1). Although the functions of LPA were recognized in the mid-1980s, its associated

Antigen receptor genes are assembled by site-specific DNA rearrangement. The recombination activator genes RAG-1 and RAG-2 are essential for this process, termed V(D)J rearrangement. The activity and stability of the RAG-2 protein have now been shown to be regulated by phosphorylation. In fibroblasts RAG-2 was phosphorylated predominantly at two serine residues, one of which affected RAG-2 activity in vivo. The threonine at residue 490 was phosphorylated by p34cdc2 kinase in vitro; phosphorylation at this site in vivo was associated with rapid degradation of RAG-2. Instability was transferred to chimeric proteins by a 90-residue portion of RAG-2. Mutation of the p34cdc2 phosphorylation site of the tumor suppressor protein p53 conferred a similar phenotype, suggesting that this association between phosphorylation and degradation is a general mechanism.

Nearly half of human cancers harbor p53 mutations, which can promote cancerous growth, metastasis, and resistance to therapy. The gain of function of mutant p53 is partly mediated by its ability to form a complex with NF-Y or p63/p73. Here, we demonstrate that TopBP1 mediates these activities in cancer, and we provide both in vitro and in vivo evidence to support its role. We show that TopBP1 interacts with p53 hot spot mutants and NF-YA and promotes mutant p53 and p300 recruitment to NF-Y target gene promoters. TopBP1 also facilitates mutant p53 interaction with and inhibition of the transcriptional activities of p63/p73. Depletion of TopBP1 in mutant p53 cancer cells leads to downregulation of NF-Y target genes cyclin A and Cdk1 and upregulation of p63/p73 target genes such as Bax and Noxa. Mutant p53-mediated resistance to chemotherapeutic agents depends on TopBP1. The growth-promoting activity of mutant p53 in a xenograft model also requires TopBP1. Thus, TopBP1 mediates mutant p53 gain of function in cancer. Since TopBP1 is often overexpressed in cancer cells and is recruited to cooperate with mutant p53 for tumor progression, TopBP1/ mutant p53 interaction may be a new therapeutic target in cancer.The tumor suppressor protein p53 generally functions through a specific DNA binding activity. Mutations of p53 are found in almost half of human cancers. Most of these mutations occur within the DNA-binding domain of p53, destroying its specific DNA binding activity. It is also well recognized that mutant p53 (mutp53) acquires new functions (gain of function) in promoting cancer cell proliferation, metastasis, genomic instability, and resistance to chemotherapy (33). The combined effects of both loss of tumor suppression and newly gained oncogenic properties may explain the high prevalence of mutp53 in human cancers.There are several potential mechanisms for mutp53 gain of function in transcriptional regulation. mutp53 can interact with NF-Y, a heterotrimeric transcription factor that recognizes the CCAAT consensus motif and regulates many cell cycle-related genes such as cyclin A, cyclin B, Cdk1, Cdc25C, etc. (7). Through the interaction, mutp53 and p300 are recruited to NF-Y target gene promoters and are responsible for aberrant expression of the above-mentioned NF-Y target genes and consequently abnormal proliferation. mutp53 can form a complex with p63/p73 and block the DNA binding activities of p63 and p73 and therefore inactivate their proapoptotic functions (9, 30, 39). mutp53 was also reported to bind non-B DNA in a DNA structure-selective manner rather than a sequence-specific manner. This binding was proposed to be the basis for its interaction with the matrix attachment region resulting in inhibition of the transcription factor recruitment and transcriptional repression (12). The full scope of mutp53 in carcinogenesis remains to be explored. Understanding its mechanistic aspect would be imperative for us to devise badly needed therapeutic strategies targeting the mutp53 gain of function in cancer.TopBP...

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