The carboxyl-terminal Src kinase (Csk) is an indispensable negative regulator for the Src family tyrosine kinases (SFKs) that play pivotal roles in various cell signalings. To understand the molecular basis of the Csk-mediated regulation of SFKs, we elucidated the crystal structure of full-length Csk. The Csk crystal consists of six molecules classified as active or inactive states according to the coordinations of catalytic residues. Csk assembles the SH2 and SH3 domains differently from inactive SFKs, and their binding pockets are oriented outward enabling the intermolecular interaction. In active molecules, the SH2-kinase and SH2-SH3 linkers are tightly stuck to the N-lobe of the kinase domain to stabilize the active conformation, and there is a direct linkage between the SH2 and the kinase domains. In inactive molecules, the SH2 domains are rotated destroying the linkage to the kinase domain. Cross-correlation matrices for the active molecules reveal that the SH2 domain and the N-lobe of the kinase domain move as a unit. These observations suggest that Csk can be regulated through coupling of the SH2 and kinase domains and that Csk provides a novel built-in activation mechanism for cytoplasmic tyrosine kinases.

Csk (carboxyl-terminal Src kinase) is a cytoplasmic tyrosine kinase that phosphorylates a critical tyrosine residue in each of the Src family kinases (SFKs) to inhibit their activities. Recently, we identified a transmembrane protein, Cbp (Csk-binding protein), that, when phosphorylated, can recruit Csk to the membrane where the SFKs are located. The Cbp-mediated relocation of Csk to the membrane may play a role in turning off the signaling events initiated by SFKs. To further characterize the Csk-Cbp interaction, we have generated a reconstituted system using soluble, highly purified proteins. Csk and phosphorylated Cbp were co-purified as a large protein complex consisting of at least four Csk⅐Cbp units. The addition of the phosphorylated, but not nonphosphorylated, Cbp to an in vitro assay stimulated Csk activity toward Src. Csk was also activated by a phosphopeptide containing the tyrosine in Cbp that binds to Csk (Tyr-314). Kinetic analysis revealed that Cbp or the phosphopeptide induced up to a 6-fold reduction in the K m for Src, indicating that the Csk⅐Cbp complex has a greater affinity for Src than free Csk. These findings suggest that Cbp is involved in the regulation of SFKs not only by relocating Csk to the membrane but also by directly activating Csk.The Src family kinases (SFKs) 1 are nonreceptor protein tyrosine kinases (PTKs) that are associated with the inner surface of plasma membrane through their fatty-acylated amino termini (1). SFKs are known to act as molecular switches that regulate a variety of cellular events, including cell growth and division, cell attachment and movement, differentiation, survival, or death (2). SFKs are ordinarily present in an inactive state in which the phosphorylated carboxyl-terminal regulatory tyrosine binds to its own SH2 domain (3). In response to an external stimulus, an SFK is activated through dephosphorylation of the carboxyl-terminal tyrosine or through binding to another protein that displaces the intramolecular interaction. The phosphorylation of the regulatory tyrosine of SFK is known to be catalyzed by another PTK, Csk (4, 5). In contrast, the phosphatases that activate SFKs have not yet been positively identified, although some candidate molecules have been proposed (6, 7). To understand the regulation of SFKs, it is essential to clarify the regulation mechanism controlling the phosphorylation and dephosphorylation of the critical carboxylterminal tyrosine.Csk is a cytoplasmic PTK consisting of an SH3, an SH2, and a kinase domain. Because it lacks an amino-terminal acylation signal and a carboxyl-terminal tyrosine, the regulatory mechanisms of Csk itself have remained unknown. A line of evidence has suggested that the SH2 and/or SH3 domain of Csk is essential for SFK regulation (8, 9). The relocation of Csk to the membrane, specifically to regions where SFKs are active, was also observed (10). In addition, a membrane-targeted form of Csk, containing the myristoylation signal of Src, more actively suppressed SFK functions (11). These facts suggeste...

These findings suggest that xCT is an independent predictive factor in GBMs.

Background: Patients with poor-grade aneurysmal subarachnoid hemorrhage (SAH) presenting with large intracerebral (ICH) or sylvian hematomas (SylH) have poor outcomes due to the mass effect of significant brain stem compression following mass effect. On the other hand, decompressive craniectomy (DC) can reduce morbidity and mortality in critically ill patients with massive ischemic infarction and severe head injury. However, the role of DC in SAH patients is not fully understood. We investigated the outcome of DC in poor-grade SAH presenting with large ICH or SylH. Methods: 110 consecutive patients with poor-grade SAH (Hunt & Kosnik (H&K) grades IV and V, and Fisher group 4) were admitted to our hospital between April 1, 1993, and July 30, 2004. We treated 57 of those who presented with large ICH or SylH using DC. We retrospectively reviewed medical charts, radiological findings, operative notes, and video records. Results: Among the 57 patients (mean age 57.8, male 29, female 28), 25 were classified as H&K grade IV and 32 as grade V. Ruptured aneurysms were located on the internal carotid artery in 11 and the middle cerebral artery in 46 patients. 50 of the aneurysms were small, 5 were medium, and 2 were large. Rerupture was preoperatively confirmed in 13 (22.8%). Hypothermia was applied to 17 (29.8%). The Glasgow Outcome Scale on discharge showed good recovery, moderate recovery, severe disability, vegetative state, and death in 8 (14.0%), 13 (22.8%), 16 (28.1%), 8 (14.0%), and 12 (21.1%), respectively. The outcomes of grade IV patients were favorable and poor in 14 (56.0%) and 10 (40.0%), respectively, and 1 (4.0%) died. Conclusion: Several experimental studies have also indicated that DC significantly improves outcome due to reduced intracranial pressure or increased perfusion pressure. Urgent DC for poor-grade SAH with space-occupying hematoma can lead to survival with good recovery in some patients.

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