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Articles by K. C Chang
Total Records ( 2 ) for K. C Chang
  C Wang , K. C Chang , G Somers , D Virshup , B. T Ang , C Tang , F Yu and H. Wang
  Cheng Wang, Kai Chen Chang, Gregory Somers, David Virshup, Beng Ti Ang, Carol Tang, Fengwei Yu, and Hongyan Wang

Drosophila larval brain neural stem cells, also known as neuroblasts, divide asymmetrically to generate a self-renewing neuroblast and a ganglion mother cell (GMC) that divides terminally to produce two differentiated neurons or glia. Failure of asymmetric cell division can result in hyperproliferation of neuroblasts, a phenotype resembling brain tumors. Here we have identified Drosophila Protein phosphatase 2A (PP2A) as a brain tumor-suppressor that can inhibit self-renewal of neuroblasts. Supernumerary larval brain neuroblasts are generated at the expense of differentiated neurons in PP2A mutants. Neuroblast overgrowth was observed in both dorsomedial (DM)/posterior Asense-negative (PAN) neuroblast lineages and non-DM neuroblast lineages. The PP2A heterotrimeric complex, composed of the catalytic subunit (Mts), scaffold subunit (PP2A-29B) and a B-regulatory subunit (Tws), is required for the asymmetric cell division of neuroblasts. The PP2A complex regulates asymmetric localization of Numb, Pon and Atypical protein kinase C, as well as proper mitotic spindle orientation. Interestingly, PP2A and Polo kinase enhance Numb and Pon phosphorylation. PP2A, like Polo, acts to prevent excess neuroblast self-renewal...

  M. E Scholz , J. D Meissner , R. J Scheibe , P. K Umeda , K. C Chang , G Gros and H. P. Kubis

The effect of constitutively activated proto-oncogene H-ras (H-rasQ61L) on the regulation of myosin heavy chain (MHC) promoter activities was investigated in rabbit satellite cell-derived muscle cell culture during the proliferation stage and early and later stages of differentiation, respectively. During proliferation, overexpression of H-rasQ61L did not affect basal level of activity of the slow MHCI/β or the fast MHCIId/x promoter luciferase reporter gene construct in transient transfection assays. By contrast, H-rasQ61L affected both MHC promoter activities during differentiation, and this effect changes from inactivation after 2 days to activation after 4 days of differentiation. The activating effect of H-rasQ61L on both MHC promoters after 4 days of differentiation was significantly reduced by LY-294002, a specific inhibitor of the phosphoinositol-3-kinase (PI3K), a downstream target of Ras. Furthermore, the protein kinase Akt (protein kinase B), a downstream target of PI3k, was activated 4 days after initiation of differentiation in myotubes overexpressing H-rasQ61L. By contrast, inhibition of another Ras downstream pathway, mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated protein kinase 1/2 (MKK1/2-ERK1/2-MAPK), increased activities of both MHC promoters, indicating a suppressive role of this pathway. Moreover, the Ras-PI3K-Akt signaling pathway is involved in the activation of MHCI/β and IId/x promoters in a later stage of differentiation of muscle cells, presumably by a known inhibiting effect of activated Akt on the MKK1/2-ERK1/2-MAPK pathway. The experiments demonstrate that during differentiation of muscle cells activated H-ras is an important regulator of MHC isoform promoter function with opposite effects during early and later stages.

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