Identification of p18 INK4c as a tumor suppressor gene in glioblastoma multiforme.

Genomic alterations leading to aberrant activation of cyclin/cyclin-dependent kinase (cdk) complexes drive the pathogenesis of many common human tumor types. In the case of glioblastoma multiforme (GBM), these alterations are most commonly due to homozygous deletion of p16(INK4a) and less commonly due to genomic amplifications of individual genes encoding cyclins or cdks. Here, we describe deletion of the p18(INK4c) cdk inhibitor as a novel genetic alteration driving the pathogenesis of GBM. Deletions of p18(INK4c) often occurred in tumors also harboring homozygous deletions of p16(INK4a). Expression of p18(INK4c) was completely absent in 43% of GBM primary tumors studied by immunohistochemistry. Lentiviral reconstitution of p18(INK4c) expression at physiologic levels in p18(INK4c)-deficient but not p18(INK4c)-proficient GBM cells led to senescence-like G(1) cell cycle arrest. These studies identify p18(INK4c) as a GBM tumor suppressor gene, revealing an additional mechanism leading to aberrant activation of cyclin/cdk complexes in this terrible malignancy.

Remote microvascular preconditioning alters specific vasoactive responses.

OBJECTIVE: The mechanism by which remote microvascular preconditioning (RMP) response is initiated was recently reported (Am J Physiol 290:H264, 2006). The goal of this study was to further characterize RMP and to investigate the extent to which RMP altered local vasoactive responses. METHODS: Arteriolar networks were examined in the cheek pouch of anesthetized (pentobarbital, 70 mg/kg) hamsters (n = 143). RMP was initiated with nitroprusside (SNP) or adenosine (ADO) via micropipette to a downstream arteriole or via tissue bath. Upstream ( approximately 800 microm), at the entrance to the network, local vasoactive responses were obtained with local micropipette application. RESULTS: The RMP response requires 10 to 15 min to manifest, and cycles down with > 5 upstream challenges (local exposures). Without challenge, the response does not cycle down over 8 h. RMP results in enhanced dilation to SNP and attenuated dilation to ADO. SNP can initiate RMP with micropipette exposure to the local downstream arteriolar segment. ADO only initiates RMP with tissue bath exposure, but at low concentrations (10(-8) M). RMP causes a shift in phosphodiesterase (PDE) maintenance of tone, as seen by using PDE inhibitors. This involves a shift from PDE4 to PDE3, and does not appear to affect PDE1 or PDE5. CONCLUSIONS: These findings are consistent with RMP inducing a fundamental shift from cAMP and towards cGMP maintenance of dilatory tone.

Initiation of remote microvascular preconditioning requires K(ATP) channel activity.

The purpose of this study was to investigate vascular preconditioning of individual microvascular networks. Prior work shows that exposure of downstream arterioles to specific agonists preconditions upstream arterioles so that they exhibit an altered local vasoactive response [remote microvascular preconditioning (RMP)]. We hypothesized that mitochondrial ATP-sensitive K+ (K(ATP)) channels were involved in stimulation of RMP. Arteriolar diameter (approximately 15 microm) was observed approximately 1,000 microm upstream of the remote exposure site in the cheek pouch of pentobarbital sodium-anesthetized (70 mg/kg) male hamsters (n = 104); all agonists were applied via micropipette. RMP was initiated by application of pinacidil (Pin), diazoxide (DZ), sodium nitroprusside (SNP), or bradykinin (BK) to the downstream vessel. After 15 min, RMP was apparent at the upstream observation site from testing of local vasoactive responses to L-arginine. Pin, DZ, SNP, and BK each stimulated RMP. To evaluate a specific role for mitochondrial K(ATP) channels in this response, 5-hydroxydecanoate was applied (via a 2nd pipette) during downstream stimulation with agonist. 5-Hydroxydecanoate blocked RMP initiated by Pin, DZ, or SNP, suggesting that mitochondrial K(ATP) channels are involved before SNP signal transduction. To verify this, we applied N(omega)-nitro-L-arginine during DZ or SNP stimulation. RMP was blocked during SNP, but not during DZ, stimulation. Thus stimulation of the RMP response requires mitochondrial K(ATP) channel activity after stimulation by nitric oxide donors.