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Chromosomal amplifications of the 11q13 genomic region are frequent in head and neck squamous cell carcinoma (HNSCC). To identify novel 11q13 amplification targets, we integrated high-resolution array-based comparative genomic hybridization and Affymetrix gene-expression profiling of eight HNSCC cell lines. We found that PPFIA1 was the highest upregulated gene in the 11q13 amplicon of HNSCC cell lines when compared with HNSCC lines without 11q13 amplification and confirmed the upregulation of PPFIA1 in primary HNSCCs by real-time PCR. Using siRNA knockdown, we investigated PPFIA1 function in three HNSCC lines using both in vitro invasion assays and wound-healing assays. Surprisingly, we found that cancer cells become more invasive when the PPFIA1 protein levels were reduced, suggesting that PPFIA1 may act as an invasion inhibitor in HNSCC. This unexpected result suggests that the 11q13 amplicon may comprise both positive and negative regulators involved in HNSCC. Our study is the first to evaluate the role of PPFIA1 in head and neck carcinogenesis and suggests a potential link between PPFIA1 activity and cell-extracellular matrix interactions. This article contains supplementary material available via the Internet at http://www.interscience.wiley.com/jpages/1045-2257/suppmat. © 2008 Wiley-Liss, Inc.

Elevated expression of the PLA2G2A phospholipase in gastric cancer (GC) is associated with improved patient survival. To elucidate function and regulation of PLA2G2A in GC, we analyzed a panel of GC cell lines. PLA2G2A was specifically expressed in lines with constitutive Wnt activity, implicating β-catenin–dependent Wnt signaling as a major upstream regulator of PLA2G2A expression. The invasive ability of PLA2G2A-expressing AGS cells was enhanced by PLA2G2A silencing, whereas cellular migration in non–PLA2G2A-expressing N87 cells was inhibited by enforced PLA2G2A expression, indicating that PLA2G2A is both necessary and sufficient to function as an inhibitor of GC invasion in vitro. We provide evidence that antiinvasive effect of PLA2G2A occurs, at least in part, through its ability to inhibit the S100A4 metastasis mediator gene. Consistent with its invasion inhibitor role, PLA2G2A expression was elevated in primary gastric, colon, and prostrate early-stage tumors, but was decreased in metastatic and late-stage tumors. There was a strong association between PLA2G2A promoter methylation status and PLA2G2A expression, suggesting that the loss of PLA2G2A expression in late-stage cancers may be due to epigenetic silencing. Supporting this, among the non–PLA2G2A-expressing lines, pharmacologic inhibition of epigenetic silencing reactivated PLA2G2A in Wnt-active lines, but in non–Wnt-active lines, a combination of Wnt hyperactivation and inhibition of epigenetic silencing were both required for PLA2G2A reactivation. Our results highlight the complexity of PLA2G2A regulation and provide functional evidence for PLA2G2A as an important regulator of invasion and metastasis in GC. [Cancer Res 2008;68(11):4277–86]

Background The synaptic cell adhesion molecules, protocadherins, are a vertebrate innovation that accompanied the emergence of the neural tube and the elaborate central nervous system. In mammals, the protocadherins are encoded by three closely-linked clusters (α, β and γ) of tandem genes and are hypothesized to provide a molecular code for specifying the remarkably-diverse neural connections in the central nervous system. Like mammals, the coelacanth, a lobe-finned fish, contains a single protocadherin locus, also arranged into α, β and γ clusters. Zebrafish, however, possesses two protocadherin loci that contain more than twice the number of genes as the coelacanth, but arranged only into α and γ clusters. To gain further insight into the evolutionary history of protocadherin clusters, we have sequenced and analyzed protocadherin clusters from the compact genome of the pufferfish, Fugu rubripes. Results Fugu contains two unlinked protocadherin loci, Pcdh1 and Pcdh2, that collectively consist of at least 77 genes. The fugu Pcdh1 locus has been subject to extensive degeneration, resulting in the complete loss of Pcdh1γ cluster. The fugu Pcdh genes have undergone lineage-specific regional gene conversion processes that have resulted in a remarkable regional sequence homogenization among paralogs in the same subcluster. Phylogenetic analyses show that most protocadherin genes are orthologous between fugu and zebrafish either individually or as paralog groups. Based on the inferred phylogenetic relationships of fugu and zebrafish genes, we have reconstructed the evolutionary history of protocadherin clusters in the teleost fish lineage. Conclusion Our results demonstrate the exceptional evolutionary dynamism of protocadherin genes in vertebrates in general, and in teleost fishes in particular. Besides the 'fish-specific' whole genome duplication, the evolution of protocadherin genes in teleost fishes is influenced by lineage-specific gene losses, tandem gene duplications and regional sequence homogenization. The dynamic protocadherin clusters might have led to the diversification of neural circuitry among teleosts, and contributed to the behavioral and physiological diversity of teleosts.