Epinephrine Increases Phosphorylation of MAP-2c in Rat Pheochromocytoma Cells (PC12 Cells) via a Protein Kinase C- and Mitogen Activated Protein Kinase-Dependent Mechanism

Structure and Functions of Microtubule Associated Proteins Tau and MAP2c: Similarities and Differences

The stability and dynamics of cytoskeleton in brain nerve cells are regulated by microtubule associated proteins (MAPs), tau and MAP2. Both proteins are intrinsically disordered and involved in multiple molecular interactions important for normal physiology and pathology of chronic neurodegenerative diseases. Nuclear magnetic resonance and cryo-electron microscopy recently revealed propensities of MAPs to form transient local structures and long-range contacts in the free state, and conformations adopted in complexes with microtubules and filamentous actin, as well as in pathological aggregates. In this paper, we compare the longest, 441-residue brain isoform of tau (tau40), and a 467-residue isoform of MAP2, known as MAP2c. For both molecules, we present transient structural motifs revealed by conformational analysis of experimental data obtained for free soluble forms of the proteins. We show that many of the short sequence motifs that exhibit transient structural features are linked to functional properties, manifested by specific interactions. The transient structural motifs can be therefore classified as molecular recognition elements of tau40 and MAP2c. Their interactions are further regulated by post-translational modifications, in particular phosphorylation. The structure-function analysis also explains differences between biological activities of tau40 and MAP2c.

Functionally specific binding regions of microtubule-associated protein 2c exhibit distinct conformations and dynamics

Microtubule-associated protein 2c (MAP2c) is a 49-kDa intrinsically disordered protein regulating the dynamics of microtubules in developing neurons. MAP2c differs from its sequence homologue Tau in the pattern and kinetics of phosphorylation by cAMP-dependent protein kinase (PKA). Moreover, the mechanisms through which MAP2c interacts with its binding partners and the conformational changes and dynamics associated with these interactions remain unclear. Here, we used NMR relaxation and paramagnetic relaxation enhancement techniques to determine the dynamics and long-range interactions within MAP2c. The relaxation rates revealed large differences in flexibility of individual regions of MAP2c, with the lowest flexibility observed in the known and proposed binding sites. Quantitative conformational analyses of chemical shifts, small-angle X-ray scattering (SAXS), and paramagnetic relaxation enhancement measurements disclosed that MAP2c regions interacting with important protein partners, including Fyn tyrosine kinase, plectin, and PKA, adopt specific conformations. High populations of polyproline II and α-helices were found in Fyn- and plectin-binding sites of MAP2c, respectively. The region binding the regulatory subunit of PKA consists of two helical motifs bridged by a more extended conformation. Of note, although MAP2c and Tau did not differ substantially in their conformations in regions of high sequence identity, we found that they differ significantly in long-range interactions, dynamics, and local conformation motifs in their N-terminal domains. These results highlight that the N-terminal regions of MAP2c provide important specificity to its regulatory roles and indicate a close relationship between MAP2c's biological functions and conformational behavior.

The epinephrine increases tyrosine hydroxylase expression through upregulating thioredoxin-1 in PC12 cells

Epinephrine is a stress hormone which is sharply increased in response to acute stress and is continuously elevated during persistent stress. Thioredoxin-1 (Trx-1) is a redox regulating protein and is induced under various stresses. Our previous study has shown that epinephrine induces the expression of Trx-1. Tyrosine hydroxylase (TH) is the major rate-limiting enzyme in catecholamine biosynthesis in response to stress. However, how TH is regulated by epinephrine is still unknown. In the present study, we found that epinephrine increased the expression of TH in a dose- and time-dependent manner in PC12 cells, which was inhibited by propranolol (β-adrenergic receptor inhibitor), but not by phenoxybenzamine (α-adrenergic receptor inhibitor). The increase of TH was also inhibited by SQ22536 (adenylyl cyclase inhibitor), H-89(PKA inhibitor) and LY294002 (phosphatidylinositol 3 kinase inhibitor). More importantly, overexpression of Trx-1 significantly enhanced the expression of TH, while Trx-1 siRNA suppressed TH expression induced by epinephrine. These results suggest that Trx-1 is involved in TH expression induced by epinephrine in PC12 cells.

Hypoxia-induced up-regulation of aquaporin-1 protein in prostate cancer cells in a p38-dependent manner

BACKGROUND/AIMS

Aquaporin-1 (AQP1) is a glycoprotein that mediates osmotic water transport, its expression has been found to correlate with tumour stage in some tumours. However, the mechanism by which AQP1 protein expression is regulated in tumor cells remains to be fully elucidated. We hypothesized that hypoxia might play an important role in AQP1 induction during tumorigenesis and at the late stages of tumor development.

METHODS

Isotonic and serum-free hypoxic models were used to investigate AQP1 expression in PC-3M human prostate cancer cells.

RESULTS

AQP1 expression was up-regulated by density-induced pericellular hypoxia and cobalt(II) chloride (CoCl(2))-induced hypoxia at the transcriptional level. Moreover, phosphorylation of p38 mitogen-activated protein kinase (MAPK) was induced by density-induced pericellular hypoxia and CoCl(2)-induced hypoxia, specific inhibitors of p38 MAPK could concentration-dependently block those effects of hypoxia on AQP1 expression. Intracellular calcium ion (Ca(2+)) and protein kinase C (PKC) were shown to be responsible for the activation of p38 MAPK pathway. In addition, AQP1 induction in dense cultures was dependent on lowered oxygen (O(2)) tension. In high cell density culture, certain secretory proteins might induce AQP1 expression indirectly.

CONCLUSION

These findings suggest that AQP1 could be induced by hypoxia at transcription level, and the regulation of AQP1 in PC-3M cells is dependent on calcium, PKC and p38 MAPK, as well as low oxygen tension.

Heparin-binding epidermal growth factor-like growth factor is a potent neurotrophic factor for PC12 cells

Heparin-binding epidermal growth factor EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor family that is expressed in many cell types. We have previously reported the effects of HB-EGF on intestinal epithelial cells and endothelial cells after exposure to ischemia/reperfusion in vivo or anoxia/reoxygenation injury in vitro. However, the effect of HB-EGF on neuronal cells is largely unexplored. In this study, we examined the effect of HB-EGF on neurite outgrowth in pheochromocytoma (PC12) cells as well as the neuroprotective effect of HB-EGF on injured PC12 cells exposed to oxygen and glucose deprivation (OGD), which mimics ischemic conditions. We found that HB-EGF significantly promotes PC12 cell neurite outgrowth and that this effect was blocked by EGF receptor (EGFR) inhibition or mitogen-activated protein kinase (MAPK) inhibition, but not by tyrosine kinase inhibition. In the face of OGD injury, HB-EGF preserves cell viability and decreases apoptosis and LDH release in PC12 cells. HB-EGF-mediated cytoprotection was abolished by EGFR inhibition and MAPK inhibition. We conclude that HB-EGF, through its interaction with the EGF receptor, activates the MAPK signaling pathway in PC12 cells under basal or injury conditions, leading to enhanced neurite outgrowth and neuroprotection against ischemic injury.