Publications (18) View all
-
Article: Tubulin polymerizing protein 1 (TPPP1) phosphorylation by Rho-associated Coiled-coil kinase (ROCK) and Cyclin dependent kinase 1 (Cdk1) inhibits microtubule dynamics to increase cell proliferation.
[show abstract] [hide abstract]
ABSTRACT: Tubulin polymerization promoting protein 1 (TPPP1) regulates microtubule (MT) dynamics via promoting MT polymerization and inhibiting Histone deacetylase 6 (HDAC6) activity to increase MT acetylation. Our results reveal that as a consequence, TPPP1 inhibits cell proliferation by delaying the G1/S-phase and the mitosis to G1-phase transitions. We show that phosphorylation of TPPP1 by Rho-associated coiled-coil kinase (ROCK) prevents its HDAC6 inhibitory activity to enable cells to enter S-phase. Whereas, our analysis of the role of TPPP1 during mitosis revealed that inhibition of its MT polymerizing and HDAC6 regulatory activities were necessary for cells to re-enter the G1-phase. During this investigation, we also discovered that TPPP1 is a novel cyclin B/Cdk1 (cyclin dependent kinase) substrate and that Cdk phosphorylation of TPPP1 inhibits its MT polymerizing activity. Overall, our results show that dual ROCK and Cdk phosphorylation of TPPP1 inhibits its regulation of the cell cycle to increase cell proliferation.Journal of Biological Chemistry 01/2013; · 4.77 Impact Factor -
Article: The phosphorylation of p25/TPPP by LIM kinase 1 inhibits its ability to assemble microtubules.
[show abstract] [hide abstract]
ABSTRACT: LIM kinase 1 (LIMK1) is a key regulator of actin dynamics as it phosphorylates and inactivates cofilin, an actin-depolymerizing factor. LIMK1 activity is also required for microtubule disassembly in endothelial cells. A search for LIMK1-interacting proteins identified p25alpha, a phosphoprotein that promotes tubulin polymerization. We found that p25 is phosphorylated by LIMK1 on serine residues in vitro and in cells. Immunoblotting analysis revealed that p25 is not a brain specific protein as previously reported, but is expressed in all mouse tissues. Immunofluorescence analysis demonstrated that endogenous p25 is co-localized with microtubules and is also found in the nucleus. Down-regulation of p25 by siRNA decreased microtubule levels while its overexpression in stable NIH-3T3 cell lines increased cell size and levels of stable tubulin. Bacterially expressed unphosphorylated p25 promotes microtubule assembly in vitro; however, when phosphorylated in cells, p25 lost its ability to assemble microtubule. Our results represent a surprising connection between the tubulin and the actin cytoskeleton mediated by LIMK1. We propose that the LIMK1 phosphorylation of p25 blocks p25 activity, thus promoting microtubule disassembly.Experimental Cell Research 01/2008; 313(20):4091-106. · 3.58 Impact Factor -
Article: Lim kinases, regulators of actin dynamics.
[show abstract] [hide abstract]
ABSTRACT: The members of the LIM kinase (LIMK) family, which include LIMK 1 and 2, are serine protein kinases involved in the regulation of actin polymerisation and microtubule disassembly. Their activity is regulated by phosphorylation of a threonine residue within the activation loop of the kinase by p21-activated kinases 1 and 4 and by Rho kinase. LIMKs phosphorylate and inactivate the actin depolymerising factors ADF/cofilin resulting in net increase in the cellular filamentous actin. Hsp90 regulates the levels of the LIM kinase proteins by promoting their homo-dimerisation and trans-phosphorylation. Rnf6 is an E3 ubiquitin ligase responsible for LIMK degradation in neurons. The activity of LIMK1 is also required for microtubule disassembly in endothelial cells. While LIMK1 localizes mainly at focal adhesions, LIMK2 is found in cytoplasmic punctae, suggesting that they may have different cellular functions. LIMK1 was shown to be involved in cancer metastasis, while LIMK2 activation promotes cells cycle progression.The International Journal of Biochemistry & Cell Biology 02/2007; 39(6):1071-6. · 4.63 Impact Factor -
Article: A role of LIM kinase 1/cofilin pathway in regulating endocytic trafficking of EGF receptor in human breast cancer cells.
[show abstract] [hide abstract]
ABSTRACT: We have previously shown that overexpression of LIM kinase1 (LIMK1) resulted in a marked retardation of the internalization of the receptor-mediated endocytic tracer, Texas red-labeled epidermal growth factor (EGF) in low-invasive human breast cancer cell MCF-7. We thereby postulate that LIMK1 signaling plays an important role in the regulation of ligand-induced endocytosis of EGF receptor (EGFR) in tumor cells by reorganizing and influencing actin-filament dynamics. In the present study, we further assessed the effect of wild-type LIMK1, a kinase-deficient dominant negative mutant of LIMK1 (DN-LIMK1) and an active, unphosphorylatable cofilin mutant (S3A cofilin) on internalization of EGF-EGFR in MDA-MB-231, a highly invasive human breast cancer cell line. We demonstrate here that a marked delay in the receptor-mediated internalization of Texas red-labeled EGF was observed in the wild-type LIMK1 transfectants, and that most of the internalized EGF staining were accumulated within transferrin receptor-positive early endosomes even after 30 min internalization. In contrast, the expression of dominant-negative LIMK1 mutant rescued the efficient endocytosis of Texas red-EGF, and large amounts of Texas red-EGF staining already reached LIMPII-positive late endosomes/lysosomal vacuoles after 15 min internalization. We further analyzed the effect of S3A cofilin mutant on EGFR trafficking, and found an efficient delivery of Texas red-EGF into late endosomes/lysosomes at 15-30 min after internalization. Taken together, our novel findings presented in this paper implicate that LIMK1 signaling indeed plays a pivotal role in the regulation of EGFR trafficking through the endocytic pathway in invasive tumor cells.Histochemie 12/2006; 126(5):627-38. · 2.59 Impact Factor -
Article: Chronic exposure to U18666A is associated with oxidative stress in cultured murine cortical neurons.
[show abstract] [hide abstract]
ABSTRACT: Findings that antioxidant treatment may be beneficial in Alzheimer's disease indicate that oxidative stress is an important factor in its pathogenesis. Studies have also suggested that cholesterol imbalance in the brain might be related to the development of neurological disorders. Previously, we have reported that U18666A, a cholesterol transport-inhibiting agent, leads to apoptosis and intracellular cholesterol accumulation in primary cortical neurons. In this study, we found that neuronal apoptosis mediated by U18666A is associated with oxidative stress in the treated cortical neurons. Cortical neurons treated with U18666A also showed decreased secretion and increased intraneuronal accumulation of beta-amyloid. The association of neuronal apoptosis with oxidative stress and Abeta accumulation may provide clues to the pathogenesis of Alzheimer's disease, as well as the role oxidative stress plays in other neurodegenerative diseases.Journal of Neurochemistry 09/2006; 98(4):1278-89. · 4.06 Impact Factor
