Galectin-1 and Galectin-3 Mediate Protocadherin-24-Dependent Membrane Localization of ß-catenin in Colon Cancer Cell Line HCT116.

Protocadherin-24 (PCDH24) is linked to the suppression of tumor growth and the inhibition of cell proliferation in the colon cancer cell line HCT116. We previously observed that ß-catenin is localized to the plasma membrane when PCDH24 is expressed in these cells, but the molecular mechanisms by which PCDH24 induces the membrane localization of ß-catenin remain largely unknown. To clarify these mechanisms, we identified molecules that interact with ectopically expressed PCDH24 in HCT116 cells using a HaloTag® pull-down assay. We found that galectin-1 and galectin-3 physically interact with PCDH24 and are retained at the plasma membrane in association with PCDH24 expression. A luciferase-based pull-down assay using HaloTag-fused galectins revealed that an intracellular region of PCDH24 (amino acids 1186-1280) is essential for this interaction. Furthermore, the over-expression of galectin-1 or -3, or the depletion of endogenous galectins by small interfering RNA modulates ß-catenin translocation. We also revealed that the retention of galectin-1 and -3 at the plasma membrane results in the inactivation of PI3K activity. From these findings, we propose a model in which the galectin-anchoring activity of PCDH24 leads to the suppression of ß-catenin signaling by the localization of ß-catenin at the plasma membrane in PCDH24-expressing HCT116 colon cancer cells.

Death effector domain-containing protein (DEDD) is required for uterine decidualization during early pregnancy in mice.

During intrauterine life, the mammalian embryo survives via its physical connection to the mother. The uterine decidua, which differentiates from stromal cells after implantation in a process known as decidualization, plays essential roles in supporting embryonic growth before establishment of the placenta. Here we show that female mice lacking death effector domain-containing protein (DEDD) are infertile owing to unsuccessful decidualization. In uteri of Dedd-/- mice, development of the decidual zone and the surrounding edema after embryonic implantation was defective. This was subsequently accompanied by disintegration of implantation site structure, leading to embryonic death before placentation. Polyploidization, a hallmark of mature decidual cells, was attenuated in DEDD-deficient cells during decidualization. Such inefficient decidualization appeared to be caused by decreased Akt levels, since polyploidization was restored in DEDD-deficient decidual cells by overexpression of Akt. In addition, we showed that DEDD associates with and stabilizes cyclin D3, an important element in polyploidization, and that overexpression of cyclin D3 in DEDD-deficient cells improved polyploidization. These results indicate that DEDD is indispensable for the establishment of an adequate uterine environment to support early pregnancy in mice.

Macrophage-derived AIM is endocytosed into adipocytes and decreases lipid droplets via inhibition of fatty acid synthase activity.

Macrophages infiltrate adipose tissue in obesity and are involved in the induction of inflammation, thereby contributing to the development of obesity-associated metabolic disorders. Here, we show that the macrophage-derived soluble protein AIM is endocytosed into adipocytes via CD36. Within adipocytes, AIM associates with cytosolic fatty acid synthase (FAS), thereby decreasing FAS activity. This decreases lipid droplet size, stimulating the efflux of free fatty acids and glycerol from adipocytes. As an additional consequence of FAS inhibition, AIM prevents preadipocyte maturation. In vivo, the increase in adipocyte size and fat weight induced by high-fat diet (HFD) was accelerated in AIM-deficient (AIM(-)(/-)) mice compared to AIM(+/+) mice. Moreover, injection of recombinant AIM in AIM(-)(/-) mice suppresses the increase in fat mass induced by HFD. Interestingly, metabolic rates are comparable in AIM(-)(/-) and AIM(+/+) mice, suggesting that AIM specifically influences adipocyte status. Thus, this AIM function in adipocytes may be physiologically relevant to obesity progression.

PCDH24-induced contact inhibition involves downregulation of beta-catenin signaling.

Elevated expression of the protocadherin LKC (PCDH24) in HCT116 colon carcinoma cells has been shown to induce contact inhibition, thereby completely abolishing tumor formation in vivo (Carcinogenesis, 2002; 23(7):1139-1148). To clarify the molecular mechanism behind this effect, we performed 2-DE/MS and DNA microarray analyses in order to compare protein and gene expression patterns of parental HCT116 and PCDH24-expressing HTC116 derivative cells. The data revealed drastic changes in phenotypic markers between parental and PCDH24-expressing cells. We found that in PCDH24-expressing cells beta-catenin, a major player in TCF/lef signaling, is retained in a submembranous location. beta-catenin retention coincided with a subsequent decrease in downstream targets of beta-catenin such as CD44, PLAUR, Myc, cyclin D1 and Met. From these findings we propose a novel model for the suppression of beta-catenin signaling by PCDH24 that leads to contact inhibition.