Recent studies suggest that lysophosphatidic acid (LPA) and its G protein-coupled receptors (GPCRs) LPA 1, LPA2, or LPA3 may play a role in the development of several types of cancers, including colorectal cancer. However, the specific receptor subtype(s) and their signal-transduction pathways responsible for LPA-induced cancer cell proliferation have not been fully elucidated. We show by specific RNA interference (RNAi) that LPA 2 and LPA3 but not LPA1 are targets for LPA-induced proliferation of HCT116 and LS174T colon cancer cells. We determined that LPA-induced colon cancer cell proliferation requires the ␤-catenin signaling pathway, because knockdown of ␤-catenin by RNAi abolished LPA-induced proliferation of HCT116 cells. Moreover, LPA activates the main signaling events in the ␤-catenin pathway: phosphorylation of glycogen synthase kinase 3␤ (GSK3␤), nuclear translocation of ␤-catenin, transcriptional activation of T cell factor (Tcf)͞lymphoid-enhancer factor (Lef), and expression of target genes. Inhibition of conventional protein kinase C (cPKC) blocked the effects, suggesting its involvement in LPA-induced activation of the ␤-catenin pathway. Thus, LPA 2 and LPA3 signal the proliferation of colon cancer cells through cPKC-mediated activation of the ␤-catenin pathway. These results link LPA and its GPCRs to cancer through a major oncogenic signaling pathway.colon cancer cell ͉ G protein-coupled receptor

The antiatherogenic property of estrogens is mediated via at least two mechanisms: first by affecting plasma lipoprotein profiles, and second by affecting the components of the vessel wall. Raising plasma apolipoprotein E (apoE) in mice protects them against dietinduced atherosclerosis (Shimano, H., Yamada, N., Katsuki, M., Gotoda, T., Harada, K., Murase, T., Fukuzawa, C., Takaku, F., and Yazaka, Y. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 1750 -1754). It is possible that estrogen may be antiatherogenic at least in part by increasing plasma apoE levels. Therefore, we studied the regulation of apoE by estrogen. A survey of 15 inbred strains of mice showed that some mouse strains responded to injections or subcutaneously implanted pellets of estradiol by raising their apoB and apoE levels and some did not. We performed detailed studies in two "responder" strains, C57L and C57BL, and two "non-responder" strains, C3H and BALBc. Responders increased their plasma apoE levels 2.5-fold. Non-responders' levels were altered ؎10%. In the responders the distribution of apoE among the plasma lipoproteins shifted from high density lipoprotein toward the apoB-containing lipoprotein fractions. In nonresponders the shift was toward high density lipoprotein. Hepatic apoE mRNA levels and relative rates of apoE mRNA transcription were unchanged in all strains, suggesting that apoE regulation occurred at posttranscriptional loci. Therefore, we measured apoE synthesis in fresh liver slices and on isolated hepatic polysomes. Two-fold increases were noted but only in responders accompanied by selective 1.5-fold increases in polysomal apoE mRNA levels. Similar increases in apoE synthesis were also observed in castrated C57BL mice given either physiological or pharmacological replacement doses of estradiol, but not testosterone, suggesting that the effect of estradiol was specific on the distribution of apoE mRNA in the translationally active polysomal pool. Next, we examined whether the effects of estrogen on apoE translation were mediated by estrogen receptors (ER). ER-␣ knockout mice and their wild-type littermates were administered estradiol. As expected, apoE levels and hepatic apoE synthesis increased more than 2-fold in the wildtype littermates, but only 20% increases in the plasma apoE and hepatic synthesis were observed in the ER knock-out mice. Hepatic apoE mRNA levels did not change in either the wild-type or the ER knock-out mice. Thus, estradiol up-regulates apoE gene expression by increasing levels of apoE mRNA in the polysomal translating pool. Furthermore, the increased polysomal recruitment of apoE mRNA is largely mediated by estrogen receptors.Estrogens may exert antiatherogenic effects either by modulating lipoprotein profiles (1) or by affecting atherosclerosispromoting factors in the vessel wall (2). Estradiol produces marked alterations in the lipoprotein profiles of mice, raising the concentrations of apoB 1 -containing particles in plasmas of strains susceptible to atherosclerosis (3, 4). In part the rise is due...

To induce dietary atherosclerosis in mice, high-fat/high-cholesterol (HF) diets are frequently supplemented with cholic acid (CA). This diet produces low plasma levels of high-density lipoprotein (HDL) and high levels of lowdensity lipoprotein (LDL). However, HF diets without any added CA, which more closely resemble human diets, increase levels of both HDL and LDL, suggesting that CA may be responsible for the lowering of HDL. Our aim was to examine the potential mechanism responsible for the lowering of HDL. Nontransgenic (NTg) C57BL mice and apoA-I-transgenic (apoAI-Tg) mice, with greatly increased basal apoA-I and HDL levels, were used. Mice were fed the following four diets: control (C), high-fat/high-cholesterol (HF), control and 1% cholate (CA) and HF 1 CA. Dietary CA reduced plasma HDL levels by 35% in NTg and 250% in apoAI-Tg mice, independent of the fat or cholesterol content of the diet. Hepatic apoA-I mRNA decreased 30% in NTg and 180% in apoAI-Tg mice. Hepatic apoA-I synthesis and apoA-I mRNA transcription rates also decreased in parallel with apoA-I mRNA levels, suggesting that the CA-induced decreases in plasma apoA-I levels occurred primarily via decreasing apoA-I mRNA transcription rates. An HF diet increased HDL levels 1.8-fold in NTg and 1.5-fold in apoAI-Tg mice. Addition of CA to the HF diet lowered HDL levels by 1.6-fold in NTg and 2.5-fold in apoAI-Tg mice. Transfection studies with the apoA-I promoter suggested the presence of a putative cis-acting element responsible for the CA-mediated down-regulation of the apoA-I promoter activity. Measurements of apoA-I regulatory protein-1 (ARP-1) mRNA, a negative regulator of the apoA-I gene in the mouse liver showed that CA increased the ARP-1 mRNA levels. Because apoA-I gene transcription alone was not sufficient to account for the lowering of plasma HDL levels, scavenger receptor-B1 (SR-B1) and hepatic lipase (HL) mRNAs levels were quantitated. The levels of SR-B1 and HL mRNA were not changed by dietary CA. These studies suggest that dietary cholate regulates plasma levels of apoA-I primarily by a transcriptional mechanism via a putative bile acid response element involving a negative regulator of apoA-I, and partly by an unidentified post-transcriptional mechanism.

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Expression of uMtCK and BCK in human placenta is highly regulated, and post-transcriptional regulation of uMtCK and BCK expression occurs in the term placenta. The coordinate regulation of uMtCK and BCK in human placenta supports the CP shuttle hypothesis. This analysis demonstrates that human placenta has high energy needs that can change rapidly; thus, a functioning CP shuttle may be important in the maintenance and termination of pregnancy.