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ABSTRACT: Vascular morphogenesis is a key process for development, reproduction, and pathogenesis. Thus understanding the mechanisms of this process is of pathophysiological importance. Despite the fact that collagen I is the most abundant and potent promorphogenic molecule known, the molecular mechanisms by which this protein regulates endothelial cell tube morphogenesis are still unclear. Here we provide strong evidence that collagen I induces tube morphogenesis by inhibiting glycogen synthase kinase 3β (GSK3β). Further mechanistic studies revealed that GSK3β activity is regulated by protein kinase D (PKD). PKD inhibited GSK3β activity, which was required for collagen I-induced endothelial tube morphogenesis. We also found that GSK3β regulated trafficking of integrin α(2)β(1) in a Rab11-dependent manner. Taken together, our studies highlight the important role of PKD in the regulation of collagen I-induced vascular morphogenesis and show that it is mediated by the modulation of GSK3β activity and integrin α(2)β(1) trafficking.
AJP Cell Physiology 08/2012; 303(7):C743-56. · 3.54 Impact Factor
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Cell cycle (Georgetown, Tex.) 03/2012; 11(6):1053-4. · 5.36 Impact Factor
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ABSTRACT: Integrins are major mediators of cancer cell adhesion to extracellular matrix. Through this interaction, integrins play critical roles in cell migration, invasion, metastasis, and resistance to apoptosis during tumor progression. Recent studies highlight the importance of integrin trafficking, endocytosis and recycling, for the functions of integrins in cancer cells. Understanding the molecular mechanisms of integrin trafficking is pivotal for understanding tumor progression and for the development of anticancer drugs.
International Journal of Cell Biology 01/2012; 2012:516789.
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ABSTRACT: The p70 ribosomal protein S6 kinase 1 (S6K1) plays a key role in cell growth and proliferation by regulating insulin sensitivity, metabolism, protein synthesis, and cell cycle. Thus, deregulation of S6K contributes to the progression of type 2 diabetes, obesity, aging, and cancer. Considering the biological and clinical importance of S6K1, a complete understanding of its regulation is critical. One of the key motifs in the activation of S6K1 is a turn motif, but its regulation is not well understood. Here we provide evidence for two mechanisms of modulating turn motif phosphorylation and S6K1 activity. First, mammalian target of rapamycin regulates turn motif phosphorylation by inhibiting its dephosphorylation. Second, we unexpectedly found that glycogen synthase kinase (GSK)-3 promotes turn motif phosphorylation. Our studies show that mammalian target of rapamycin and GSK-3 cooperate to control the activity of S6K1, an important regulator of cell proliferation and growth. Our unexpected results provide a clear rationale for the development and use of drugs targeting GSK-3 to treat diseases such as diabetes, cancer, and age-related diseases that are linked to improper regulation of S6K1.
Proceedings of the National Academy of Sciences 11/2011; 108(47):E1204-13. · 9.68 Impact Factor
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Cell cycle (Georgetown, Tex.) 07/2010; 9(13):2483-4. · 5.36 Impact Factor
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ABSTRACT: Hyperactivation of Ras-ERK1/2 signaling is critical to the development of many human malignancies, but little is known regarding the specific contribution of ERK1 or ERK2 to oncogenic processes. We demonstrate that ERK2 but not ERK1 signaling is necessary for Ras-induced epithelial-to-mesenchymal transformation (EMT). Further, ERK2 but not ERK1 overexpression is sufficient to induce EMT. Many ERK1/2-interacting proteins contain amino acid motifs, e.g., DEF or D-motifs, which regulate docking with ERK1/2. Remarkably, ERK2 signaling to DEF motif-containing targets is required to induce EMT and correlates with increased migration, invasion, and survival. Importantly, the late-response gene product Fra1 is necessary for Ras- and ERK2-induced EMT through upregulation of ZEB1/2 proteins. Thus, an apparent critical role for ERK2 DEF motif signaling during tumorigenesis is the regulation of Fra1 and the subsequent induction of ZEB1/2, suggesting a potential therapeutic target for Ras-regulated tumorigenesis.
Molecular cell 04/2010; 38(1):114-27. · 14.61 Impact Factor
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ABSTRACT: The major participants of the Ras/ERK and PI3-kinase (PI3K) pathways are well characterized. The cellular response to activation of these pathways, however, can vary dramatically. How differences in signal strength, timing, spatial location, and cellular context promote specific cell-fate decisions remains unclear. Nuclear transport processes can have a major impact on the determination of cell fate; however, little is known regarding how nuclear transport is regulated by or regulates these pathways. Here we show that RSK and Akt, which are activated downstream of Ras/ERK and PI3K, respectively, modulate the Ran gradient and nuclear transport by interacting with, phosphorylating, and regulating Ran-binding protein 3 (RanBP3) function. Our findings highlight an important link between two major cell-fate determinants: nuclear transport and the Ras/ERK/RSK and PI3K/Akt signaling pathways.
Molecular Cell 03/2008; 29(3):362-75. · 14.18 Impact Factor
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ABSTRACT: Matrix metalloproteinase (MMP)-9 plays a key role in tumor invasion. Inhibitors of MMP-9 were screened from Metasequoia glyptostroboides (Dawn redwood) and one potent inhibitor, isoginkgetin, a biflavonoid, was identified. Noncytotoxic levels of isoginkgetin decreased MMP-9 production profoundly, but up-regulated the level of tissue inhibitor of metalloproteinase (TIMP)-1, an inhibitor of MMP-9, in HT1080 human fibrosarcoma cells. The major mechanism of Ras-dependent MMP-9 production in HT1080 cells was phosphatidylinositol 3-kinase (PI3K)/Akt/nuclear factor-kappaB (NF-kappaB) activation. Expression of dominant-active H-Ras and p85 (a subunit of PI3K) increased MMP-9 activity, whereas dominant-negative forms of these molecules decreased the level of MMP-9. H-Ras did not increase MMP-9 in the presence of a PI3K inhibitor, LY294002, and a NF-kappaB inhibitor, SN50. Further studies showed that isoginkgetin regulated MMP-9 production via PI3K/Akt/NF-kappaB pathway, as evidenced by the findings that isoginkgetin inhibited activities of both Akt and NF-kappaB. PI3K/Akt is a well-known key pathway for cell invasion, and isoginkgetin inhibited HT1080 tumor cell invasion substantially. Isoginkgetin was also quite effective in inhibiting the activities of Akt and MMP-9 in MDA-MB-231 breast carcinomas and B16F10 melanoma. Moreover, isoginkgetin treatment resulted in marked decrease in invasion of these cells. In summary, PI3K/Akt is a major pathway for MMP-9 expression and isoginkgetin markedly decreased MMP-9 expression and invasion through inhibition of this pathway. This suggests that isoginkgetin could be a potential candidate as a therapeutic agent against tumor invasion.
Molecular Cancer Therapeutics 12/2006; 5(11):2666-75. · 5.23 Impact Factor
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ABSTRACT: Active Ras proteins contribute to breast carcinogenesis and progression. Here, we provide evidence that active H-Ras regulates the expression and activity of the E2F family of transcription factors in SUM-159 breast carcinoma cells. In addition, we show by using a DNA-binding mutant of E2F, as well as expression of specific E2Fs that are transcriptionally active, that the active E2Fs1-3 can mediate the H-Ras-dependent invasion of SUM-159 cells. The inhibitory E2Fs4-5, in contrast, do not influence invasion. One mechanism by which the active E2Fs promote H-Ras-dependent invasion seems to be their ability to increase expression of the beta4 integrin subunit, a component of the alpha6beta4 integrin that is known to enhance carcinoma invasion. Specifically, expression of E2Fs1-3 increased beta4 mRNA, protein, and cell surface expression. The active E2Fs were unable to stimulate invasion in cells that expressed a beta4 short hairpin RNA. This effect of the active E2Fs on beta4 expression does not seem to result from E2F-mediated beta4 transcription because the beta4 promoter lacks known E2F binding motifs. In summary, the data reported here indicate a novel mechanism by which H-Ras can promote the invasion of breast carcinoma cells. This mechanism links active H-Ras, transcriptionally active E2F, and the alpha6beta4 integrin in a common pathway that culminates in enhanced alpha6beta4-dependent invasion.
Cancer Research 07/2006; 66(12):6288-95. · 7.86 Impact Factor
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ABSTRACT: ErbB2 (HER2, Neu) and Ras play key roles in tumor invasion and metastasis. We identified a novel mechanism by which integrin alpha(6)beta(4) regulates ErbB2 expression, Ras activation, and the invasion of breast carcinoma cells. Here we show that integrin alpha(6)beta(4) regulates Ras activity especially in serum-depleted condition. Down-regulation of beta(4) integrin by beta(4) short hairpin RNA (shRNA) decreased Ras activity and carcinoma invasion whereas reexpression of this integrin restored Ras activity. ErbB2, a binding partner of epidermal growth factor receptor (EGFR), and EGFR modulated Ras activity, and integrin alpha(6)beta(4) regulated phospho-EGFR level without affecting EGFR expression. We also found that integrin alpha(6)beta(4) is involved in ErbB2 expression. Depletion of beta(4) by shRNA reduced ErbB2 protein level without affecting ErbB2 mRNA level and reexpression of beta(4) increased ErbB2 protein level. Reduction of eukaryotic initiation factor 4E, a rate-limiting factor for cap-dependent translation, decreased ErbB2 protein level, and beta(4) shRNA cells exhibited a shift in ErbB2 mRNA to light polysomes compared with control cells. These results show that integrin alpha(6)beta(4) regulates ErbB2 through translational control. In summary, we propose a novel mechanism for ErbB2 up-regulation and Ras activation in serum-depleted breast cancer cells; integrin alpha(6)beta(4) regulates the expression of ErbB2 and the subsequent phosphorylation of EGFR and activation of Ras. These findings provide a mechanism that substantiates the reported role of alpha(6)beta(4) in carcinoma invasion.
Cancer Research 04/2006; 66(5):2732-9. · 7.86 Impact Factor
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ABSTRACT: Hypoxia plays a key role in tumor cell survival, invasion, and metastasis. Here we show that hypoxia increases tumor cell invasion by the modulation of Rab11, an important molecule for vesicular trafficking, especially membrane protein recycling and translocation of proteins from trans-Golgi network to plasma membrane. Dominant-negative Rab11 dramatically decreased hypoxia-induced invasion of MDA-MB-231 breast carcinoma cells without affecting cell apoptosis. Hypoxia-induced Rab11 trafficking is regulated by microtubule stability, as evidenced by the findings that hypoxia increases Glu tubulin and that colchicine blocks Rab11 trafficking and invasion. Inhibition of GSK-3beta activity by hypoxia seems to be central to microtubule stabilization and invasion. In fact, expression of a dominant-negative GSK-3beta was sufficient to stimulate invasion in normoxia. One target of Rab11-mediated trafficking that contributes to invasion is the integrin alpha6beta4. Hypoxia induced a significant increase in alpha6beta4 surface expression but it had no effect on the surface expression of alpha3beta1. This increase is dependent on Rab11 and stable microtubules. In summary, we identify vesicle trafficking as a novel target of hypoxic stimulation that is important for tumor invasion.
Cancer Research 05/2005; 65(7):2761-9. · 7.86 Impact Factor
