Silicon Investor (SI) -- The First Internet Community

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

Biotech / Medical : Biotech News -- Ignore unavailable to you. Want to Upgrade?

To: Ian@SI who wrote (2829)	12/28/2003 1:02:42 PM
From: scaram(o)uche	Read Replies (1) \| Respond to of 7143

J Biol Chem. 2003 Oct 30 [Epub ahead of print]. Characterization of the protein kinase activity of TRPM7/ChaK1, a protein kinase fused to TRP ion channel. Ryazanova LV, Dorovkov MV, Ansari A, Ryazanov AG. Pharmacology Dept., UMDNJ-R.W.Johnson Medical School, Piscataway, NJ 08854. Channel-kinase TRPM7/ChaK1 is a member of recently discovered family of protein kinases called alpha-kinases that display no sequence homology to conventional protein kinases. It is an unusual bi-functional protein that contains an alpha-kinase domain fused to an ion-channel. TRPM7/ChaK1 channel has been characterized using electrophysiological techniques and recent evidence suggests that it may play a key role in the regulation of magnesium homeostasis. However, little is known about its protein kinase activity. To characterize the kinase activity of TRPM7/ChaK1 we expressed the kinase catalytic domain in bacteria. ChaK1-cat is able to undergo autophosphorylation and to phosphorylate myelin basic protein and histone H3 on serine and threonine residues. The kinase is specific for ATP, and cannot use GTP as a substrate. ChaK1-cat is insensitive to staurosporine (up to 0.1 mM), but can be inhibited by rottlerin. Since the kinase domain is physically linked to an ion channel, we investigated the effect of ions on ChaK1-cat activity. The kinase requires Mg2+ (optimum at 4-10 mM) or Mn2+ (optimum at 3-5 mM), with activity in the presence of Mn2+ being two orders of magnitude higher then in the presence of Mg2+. Zn2+ and Co2+ inhibited ChaK1-cat kinase activity. Ca2+ at the concentration up to 1mM did not affect kinase activity. Considering intracellular ion concentration, our results suggest that among divalent metal ions only Mg2+ can directly modulate TRPM7/ChaK1 kinase activity in vivo. J Biol Chem. 2003 Oct 31;278(44):42867-76. Epub 2003 Aug 06. Regulation of a TRPM7-like current in rat brain microglia. Jiang X, Newell EW, Schlichter LC. Division of Cellular and Molecular Biology, Toronto Western Research Institute, 399 Bathurst Street, Toronto, Ontario M5T 2S8, Canada. Non-excitable cells use Ca2+ influx for essential functions but usually lack voltage-gated Ca2+ channels. The main routes of Ca2+ entry appear to be store-operated channels or Ca2+-permeable non-selective cation channels, of which the magnesium-inhibited cation (or magnesium-nucleotide-regulated metal cation) current has received considerable recent attention. This current appears to be produced by one of the recently cloned transient receptor potential (TRP) channels, TRPM7. In this study of rat microglia, we identified TRPM7 transcripts and a prevalent current with the hallmark biophysical and pharmacological features of TRPM7. This is the first identification of a TRPM7-like current in the brain. There is little known about how members of the TRPM sub-family normally become activated. Using whole-cell patch clamp recordings from rat microglia, we found that the TRPM7-like current activates spontaneously after break-in and that the current and its activation are inhibited by elevated intracellular Mg2+ but not affected by cell swelling or a wide range of intracellular Ca2+ concentrations. The TRPM7-like current in microglia appears to depend on tyrosine phosphorylation. It was inhibited by several tyrosine kinase inhibitors, including a peptide (Src 40-58) that was shown previously to inhibit Src actions, but not by inactive drugs or peptide analogues. The current did not depend on the cell activation state; i.e. it was the same in microglia recently removed from the brain or when cultured under a wide range of conditions that favor the resting or activated state. Because TRPM7 channels are permeable to Ca2+, this current may be important for microglia functions that depend on elevations in intracellular Ca2+. Cell. 2003 Jul 25;114(2):191-200. Regulation of vertebrate cellular Mg2+ homeostasis by TRPM7. Schmitz C, Perraud AL, Johnson CO, Inabe K, Smith MK, Penner R, Kurosaki T, Fleig A, Scharenberg AM. Department of Pediatrics, University of Washington and Children's Hospital and Regional Medical Center, Seattle, WA 98195, USA. TRPM7 is a polypeptide with intrinsic ion channel and protein kinase domains whose targeted deletion causes cells to experience growth arrest within 24 hr and eventually die. Here, we show that while TRPM7's kinase domain is not essential for activation of its channel, a functional coupling exists such that structural alterations of the kinase domain alter the sensitivity of channel activation to Mg(2+). Investigation of the relationship between Mg(2+) and the cell biological role of TRPM7 revealed that TRPM7-deficient cells become Mg(2+) deficient, that both the viability and proliferation of TRPM7-deficient cells are rescued by supplementation of extracellular Mg(2+), and that the capacity of heterologously expressed TRPM7 mutants to complement TRPM7 deficiency correlates with their sensitivity to Mg(2+). Overall, our results indicate that TRPM7 has a central role in Mg(2+) homeostasis as a Mg(2+) uptake pathway regulated through a functional coupling between its channel and kinase domains.